Do you believe that lead boolits actually obturate (swell up) when fired? Yes or No

[Russel Nash]

Do you believe that lead boolits actually obturate (swell up) when fired? Yes or No

[chief3]

Yes they do. I have seen plenty of evidence from both high speed cameras and recovered boolits.
Also, the minnie bullet of Civil War fame wpuld never have worked without obturation.

[Russel Nash]

Man! That was quick!

I might have to go back and add a third option. Yeah, I already knew about the Minie balls and their design.

But you didn't vote yet! Be sure to vote.

[Russel Nash]

chief3 wrote:


I have seen plenty of evidence from both high speed cameras and recovered boolits.


Do you have links to any of these videos and/or pics of the recovered boolits?

[Russel Nash]

Please, people, just vote. Let the poll kinda run it's course for a while and then you can chime in later with your opinions. Thanks!

[454PB]

I had to vote no.

They can only obturate if one of the critical measurements isn't correct.

[Marlin Hunter]

yes to a point. you have high pressure applied to the base of a bullet and a little more than atmospheric pressure, combined with compression of the air during acceleration, at the front of the bullet. the rear wants to go faster than the front, so it would distort or compress the lead a little to make it expand. I don't think it would expand to fill in an air gap between the barrel and a smaller diameter boolit, but it would cause greater pressure and sealing of a well fitting boolit.

I might have the wrong definition of Obturate.

[Marlin Hunter]

Please, people, just vote. Let the poll kinda run it's course for a while and then you can chime in later with your opinions. Thanks!

oops

I started typing before you posted that.

[Edubya]

When that boolit hits the lands there (if not the forcing cone) is a bit of friction. It only seems reasonable that it would obturate then, if not before.
EW

[Russel Nash]

Marlin Hunter wrote:


the rear wants to go faster than the front, so it would distort or compress the lead a little to make it expand.

And that my friends is what brought me to start a poll here.

From my high school and college physics/chemistry classes, there are only four states of matter:

1. gases
2. liquids
3. solids
4. plasma

Also, in those classes, I learned that of the first 3, only the gases are compressible. Liquids are not compressible, and that explains why hydraulic pistons work on something like a crane or a back-hoe. And why they don't use pneumatic rams or pistons for some stuff. Solids aren't compressible, like a block of steel. So my thoughts are that a cylindrical piece of lead is a solid, and therefore can't compress or be compressible. Unless of course it was surrounded all around by something strong like a steel swaging die and pressed into a particular shape.

What I am saying is that with the exception of very soft lead and/or Minie balls, I think lead boolit obturation might just be a myth.

[felix]

Why do tight necks cause trouble? ... felix

[Springfield]

There is a large difference between compressing and moving material. Hit a bullet with a hammer and tell me it doesn't change shape. Or for that matter, using your reasoning, a bullet sizer couldn't possibly reduce the diameter of a bullet. But we know it does. You are just using the wrong term. "The mechanism by which an undersized soft metal projectile enlarges to fill the barrel is, for hollow-base bullets, due to expansion from gas pressure within the base cavity and, for solid-base bullets, upsetting - the combined shortening and thickening that occurs when a malleable metal object is struck forcibly at one end".

[Russel Nash]

Springfield wrote:


Hit a bullet with a hammer and tell me it doesn't change shape.

I am assuming that you are putting the cast boolit like on a heavy duty steel table or an anvil or out on a concrete sidewalk. And then you are whacking it with a hammer.

If so, then that really isn't an apples to apples comparison in my opinion

Springfield wrote:


"The mechanism by which an undersized soft metal projectile enlarges to fill the barrel is, for hollow-base bullets, due to expansion from gas pressure within the base cavity and, for solid-base bullets, upsetting - the combined shortening and thickening that occurs when a malleable metal object is struck forcibly at one end".


I couldn't get all that to fit on the thread's subject line.

[Bullshop]

If boolits didn't obturate a muzzle loader wouldn't work very well.
I sell lot of conicel boolits for ML. I was curious to see how hard a boolit would be small enough in diameter to load easily but still obturate enough to give good accuracy.
A test was undertaken using annealed .451" jacketed bullets loaded on a fairly stiff charge of 777 in a 45 cal in line. Accuracy was excellent and the recovered bullets showed normal engraving proving that they did indeed obturate sufficiently to act the same as a bullet starting out at groove diameter in stead of starting out at bore diameter.
BIC/BS

[Russel Nash]

Hmmn....(sigh)

I guess I should have narrowed down this poll even more so that it EXCLUDED muzzle loaders.

I don't have a muzzleloader. I am not really interested in them. Plus, I already mentioned above that I already knew about the Minie balls.

(sigh)

[462]

I have neither a scientific nor metallurgical background, and never went to college, but, from what I've experienced, Felix is spot on.

[Jim]

Russell, with all due respect, my friend, I think your mind is made up and I don't think anyone is going to change it for you. Having said that, I don't think labaratory proof would convince you of obturation.

[Edubya]

Does a golf ball or a baseball compress? They ain't in a cylinder or being held against a solid barrier. I don't know if it can be explained in simple language and I'm just a simple man, so I'll leave it up to you to make your own decision as I have mine.
EW

[felix]

Gosh, darn, waddya' know! ... felix

[runfiverun]

well that all stopped me from going into the use of 428 boolits in my 430 sized 44-40 bbl.

[lwknight]

How can a boolit not obturate with 50,000 pounds pressure applied to the base?

[chief3]

Wish I had the pics I saw years ago but I can't even remember where they were published. They had a white background with referance lines that showed the boolit was larger than the bore. Don't know how they did it but it looked good. This was about 45 yrs ago.

[Russel Nash]

Last I checked, a baseball and a golfball was NOT made up of one singular homogeneous mixture.

There are several different materials involved in the construction of both.

slight thread drift ahead.... I remember hearing that one season of major league baseball had more homeruns because the internals of the ball were wound more tightly with string. This was back when the baseballs were wound by hand. The baseballs were made overseas, and the people were happier because the weather was better and the harvest season was more bountiful.

I guess they have computer controlled machines that do the winding now:

http://www.enotes.com/how-products-encyclopedia/baseball

[Russel Nash]

lwknight wrote:


How can a boolit not obturate with 50,000 pounds pressure applied to the base?


Conversely, if a boolit were to obturate too much then your gun would go KABOOM!

Right?

:confused:

[felix]

Right on both accounts exhibited above. ... felix

[jbunny]

my bud has 4 sweedish remmington rolling block rifles 50-70. 3 of those have
the hex metford rifleing, he shoots mild loads 31 gr of 3031 behind a 400 gr
soft lead boolit. the boolits are cast round. we recovered a whole pile of boolits
this spring after the snow melted. the boolits were all hex shaped. u be the judge.
jb

[Greg in Malad]

Ok fellers,
I have fired .450 diameter conicals in a .458 groove diameter muzzleloader barrel. The bullets would drop to the bottom of the barrel by their own weight. When shot into wet newspaper they had rifling engraved from nose to base.

[lwknight]

well that all stopped me from going into the use of 428 boolits in my 430 sized 44-40 bbl.
__________________

The boolit has to be big enough to seal the barrel first. Then all that pressure on the base will flatten most of the boolit to expand it to the barrel size. Jacjeted bullet bases do not expand on inpact with water, Full metal jacketed bullets do not expand on anything short of cold steel impact. The only way to prove or disprove would be to use the same bullet in 2 dfferent sized barrels being that one is larger than the starting size of the bullet.

When the recovered slugs are measured, if shot at high pressure loads, the base will be fully obturated to the bore/grooves. It may not work with cast boolits that are undersized because the gases will cut away the lead as it passes around the boolit. Resulting in leading the barrel.

We know that boolits that are too hard for a mild load can lead up a bore because they don't bump up to size.

[Frozone]

Last I checked, a baseball and a golfball was NOT made up of one singular homogeneous mixture.

It doesn't matter. take a piece of steel bar stock and use it as a bat, swing it at an airborne ball of lead and see what it looks like. It'll be distorted at the impact point and all that was in front was air. And just to head off a bit of argument, it wouldn't matter if you used a gas, a liquid, or a solid you'd get the same effect. Only the degree of displacement will vary. If this wasn't true you'd have a hard time cutting steel with a water jet.

[runfiverun]

We know that boolits that are too hard for a mild load can lead up a bore because they don't bump up to size.

xactly,but the softer ones i do use will, the larger ones won't chamber.
i have to size these down from 430 to 428 however i have exactly zero leading.
....now.......
but i have to use a stout load of 2400 to get there.
i don't like to bump up any type of lead in a revolver,rifle what have you but you do what it takes to make things work correctly.
i have often wondered why fmj's in rifle and pistol variety have a dished out base?????
hmmm.
the ones i have recovered after being fired that didn't start that way sure ended up with one. lead compresses under pressure,if it didn't we wouldn't be able to swage boolits or extrude pipe while the lead is cold.

[Deliverator]

Springfield wrote:



I am assuming that you are putting the cast boolit like on a heavy duty steel table or an anvil or out on a concrete sidewalk. And then you are whacking it with a hammer.

If so, then that really isn't an apples to apples comparison in my opinion

Springfield wrote:



I couldn't get all that to fit on the thread's subject line.

Here is a better one, take a baseball bat, then toss a piece of lead into the air and strike it with the bat. Then look at the piece of lead and see how it now has a distinct imprint of a baseball bat.

Same basic principle, a force is being exerted suddenly against a soft solid causing a distortion of the material. When this happens in a barrel there is something there to stop it from turning into a flat piece of metal. A force is a force is a force is a force and so on and so forth. It is the EXACT same principle as what happens when a flying bullet strikes a solid steel plate. Its all the same. And if you even TRY to deny that, you are just denying it to get an argument.

[Russel Nash]

I never said that lead was NOT malleable.

I'm still saying that my own personal jury is out on this obturation concept.

[Russel Nash]

runfiverun wrote:


lead compresses under pressure

for the sake and sanity of scientific discussion let's NOT use the word compress when it comes to talking about a solid like a lead boolit.

[Russel Nash]

Deliverator wrote:


It is the EXACT same principle as what happens when a flying bullet strikes a solid steel plate.

No, it is not.

A lead boolit contained along its length by a steel bore or barrel has no where else to expand to. It can only travel out the bore, in one direction.

A flying bullet striking a steel plate is not really contained by anything.

[Russel Nash]

runfiverun wrote:


the ones i have recovered after being fired that didn't start that way sure ended up with one.

In what medium did you recover these bullets in/from?

[Bullshop]

Why are you tossing out the obvious with muzzle loaders? A gun barrel works the same no matter how it is loaded.
Anyway you didn't pay any attention to what I said about the jacketed .451" Hornady 300gn XTP bullet being fired in the muzzle loader. It was not even close to the hollow base mini you mentioned then wrote off as what a muzzle loader shoots.
It would not have made any difference weather it was fired in a muzzle loader or a cartridge rifle, it would have done the same thing.
I am willing to bet if you took the same bullet and charged a 45/70 case to the same pressure as the ML the same .451" Hornady bullet will be fully engraved by a .458 groove barrel.
The problem you have is you are putting too much faith it your higher education and keeping a very closed mind. I think the issue is that you are stuck on a word, compressed. Compressed is the wrong word here so technically you are right the bullet mass is not compressing it is swagging. It is becoming fluid under pressure and flowing to the areas of least resistance, the grooves.
If you have noticed a recovered bullet or boolit after firing is not the same shape that it was before firing even if there is no expanding from impact.
I remember reading something from Dr. Mann where he was shooting base band bullets.
In this case he was shooting .257" diameter jacketed bullets with a .264" gas check crimped on its base.
He was firing them in a .264 caliber rifle possibly a 256 Newton. His idea was to achieve ultra high velocity by reducing drag in the barrel by using this base band bullet as he called it. Most of the length of the bullet was riding the lands ( bore ride) and only the gas check was full diameter for caliber.
What he found was that the recovered bullets were fully engraved for the length of the bullet. Not compressing but swagging up to caliber, same as they do in a die under pressure, same as all factory lead core jacketed bullets.
Your obviously a smart fellow so why don't you get this?
BIC/BS

[Deliverator]

Deliverator wrote:



No, it is not.

A lead boolit contained along its length by a steel bore or barrel has no where else to expand to. It can only travel out the bore, in one direction.

A flying bullet striking a steel plate is not really contained by anything.

Actually it will expand in every direction until it interacts with something stronger than the force of its expansion, thus being contained. Same thing with when it strikes a steel plate. The steel plate is stronger than all other directions thus why it expands outward until its energy is expended.

I thought you were supposed to be some kind of scientists that knows stuff...

[Russel Nash]

Frozone wrote:


..... water jet.


Some...not all "water jets" are also actually using an abrasive like garnet to cut whatever material.

http://science.howstuffworks.com/question553.htm

That is also 55,000 psi through an orifice that is about 10 thou to 15 thou in diameter

For a bullet, we are talking about...oh...I dunno...24,000 psi over a 356 thou diameter circular surface.

[Russel Nash]

Deliverator wrote:


thought you were supposed to be some kind of scientists that knows stuff...




why so snarky?

And, NO, I never did say I was a scientist.

[Russel Nash]

Bullshop wrote:


What he found was that the recovered bullets were fully engraved for the length of the bullet. Not compressing but swagging up to caliber, same as they do in a die under pressure, same as all factory lead core jacketed bullets.


Just curious then...what were the lengths of the boolits, the pro-jo's before they were shot vs. the lengths of the boolits after they were shot/recovered?

[Russel Nash]

Bullshop also wrote:


Your obviously a smart fellow so why don't you get this?


Do I detect a little bit of snarkiness there too?

[high standard 40]

Sounds like a troll to me. Classic. I've seen them on other boards. It's how they get their kicks. The smart thing to do is not argue with him.

[Heavy lead]

This is somewhat of a confusing thread, but obturation does happen IF it needs to IF the projectile is soft enough to respond to the pressure it is being pushed by whether it be in an air rifle or a 65,000 psi Weatherby magnum with a Barnes Triple Shock, simple as that.
Maybe I'm splitting hair's here with the definition, but would not obturation be the action of a bullet being pinched down by a tight spot in the barrel and then opening back up to fill the lands and grooves as it traveled throught the bigger part of the barrel as well?
Also wouldn't the definition of obturation also include a bullet or boolit taking on different land and groove pitches as it traveled through a gain twist rifled barrel as well?

[357maximum]

Do you believe that lead boolits actually obturate (swell up) when fired? Yes or No


I do not believe it....I know it.

Why ask a question ...PM me and invite to join the discussion and then argue anything that is posted that goes against the grain of the state your brain? now that there is a real question. A discussion is pointless when one side fails to discuss things....at that point it is an argument....and is what I think you truly wanted.

You seem to have YOUR closed mind made up otherwise, and I do not feel like argueing common sense observations with you......so I will leave it at YES.

[missionary5155]

Good evening
If solids are not compressable.. How is it that atomic matter compressed to reach crtical state ? I realise an EXPLOSION is used but compression is compression.
Pure lead (1-40) must do something when Smacked in the rear by Blackpowder otherwise my borewidth nose riding boolits would not have rifling engraved on those noses.
Happy New Year everyone.

[Marlin Hunter]

How can a boolit not obturate with 50,000 pounds pressure applied to the base?

The same thing happens when a bug hits your windshield at 65mph. It obturates all over the windshield.

[Old Caster]

I recently saw an article in a magazine where large lead bullets were fired out of different length rifle barrels (down to two inches) and it had pictures of what the bullets looked like when they were leaving the barrel and it was stunning how much fatter the bullets looked in the back than in the front. It was maybe double size. I don't remember for sure what magazine it was but I think I gave it to one of the guys in my pellet league and will ask next Thursday about it and will post if I find it. I picked it up at the range in the free magazine section so it is likely that it was at least a few years old. I believe it was a BPCR magazine.

[softpoint]

Somewhere I have a chart that I got off of a cast bullet site that has the pressure required to "upset" bullets of different alloys. I believe the article states that the optimum load for a cast bullet is one that meets the pressure required to "upset" the bullet out of a particular alloy, but not so much in excess of that that the lube fails, and leading starts, or the bullet is accelerated so fast it "skips" over the rifling. Now, I can't see what goes on inside my barrel, but some things would indicate this is true. One is that you can minimize or eliminate leading by using a slower burning powder to achieve a given velocity. Light loads with fast burning powder, on the other hand, lead for the opposite reason, I have seen a hard cast .44 caliber bullet lead badly in a .44 magnum with only 6 grains of Unique. Leading might stop at 10 grains, or be less. But as you try to get higher velocity ,leading will come back again, unless you go to a slower burning powder, such as 2400. Now, individual guns can vary widely how they respond, but most shooters here at this site have observed this. Isn't this due to obturation, or lack of it? My guess is that it is.

[montana_charlie]

for the sake and sanity of scientific discussion let's NOT use the word compress when it comes to talking about a solid like a lead boolit.
Would you accept a term like 'swage"?

Swaging happens rather slowly compared to the firing of a cartridge.
But, the pressure exerted by a powder charge is easily equal to the pressure developed by a swaging press.

The swaging die has an internal 'shape' as does a barrel have one.
Under pressure the lead exactly fills the swaging die, as a bullet fills a barrel.
Because the swaging die is closed on the end opposite from the ram, the action can occur slowly.
Because the action happens so fast, the same reforming of the lead takes place in a barrel that has an open end.
With swaging, the lead is 'held back' against the pressure of the ram by the closed end of the die.
In a barrel the lead is 'held back' against the pressure wave by enertia.

Obturation happens, Russel. You may as well accept it.
You won't accept the action of a minnie ball, and I understand why you don't think that is adequate proof.

But, if obturation did not occur, the Maxi-Ball couldn't work...and it doesn't depend on a hollow base.
It is a bullet that starts out at slightly less than bore diameter, and is bumped up to groove diameter when fired.

If something is making you doubt that obturation is possible, that may be from using hard alloys with smokeless powder.
Hard alloys don't bump as easily, and smokeless doesn't bump very much, sometimes.

CM

[Bullshop]

Please define snarkiness. I am not sure what it means. If it means a person loosing patience with someone that refuses to accept the truth after the truth has been repeatedly offered by multiple persons then yes I have become snarky.
If it means a person loosing patience with someone after that someone has been repeatedly proven wrong and the person in the wrong trying to hide the fact by accusing those offering the truth of wrong doing then yes again I am a snarker, possibly a mega magnum master of snarkology.
Maybe before I go any farther with all that it could mean you should give me the real meaning. I may be totally off base and it could mean something like a person so knowledgeable about that of which they speak that they virtually know everything there is to know about it. If so thank you very much !!! Very observant and nice of you to say so.
God Bless
BIC/BS

[lwknight]

Russel, The body of the group has a well founded opinion from experience,trial and error and logic , and you are not going to change it. You are outnumbered 10 to 1 at least (discounting those on the fence)
If you want to be a sucessful heretic you will have to do your experiments in silence and publish the r sults with sufficiently recorded details to sell the unpopular idea to anyone.

[waksupi]

Gentlemen, keep the tone polite, please.

[jhrosier]

Wish I had the pics I saw years ago but I can't even remember where they were published. ....

F.W.Mann,The Bullet's Flight From Powder to Target, 1909

Jack

[Bullshop]

We just looked up snarky. Our dictionary said it means to be testy or irritable.
OK OK I am guilty.
But hay you come on up here and live with little daylight and temps in the -30's and see if you don't get snarky.
You think I am snarky this time of year man you best not get into it with BS Mom.
Please forgive my snarkiness. I will try to do better.
Blessings
BIC/BS

[405]

Marlin Hunter wrote:



And that my friends is what brought me to start a poll here.

From my high school and college physics/chemistry classes, there are only four states of matter:

1. gases
2. liquids
3. solids
4. plasma

Also, in those classes, I learned that of the first 3, only the gases are compressible. Liquids are not compressible, and that explains why hydraulic pistons work on something like a crane or a back-hoe. And why they don't use pneumatic rams or pistons for some stuff. Solids aren't compressible, like a block of steel. So my thoughts are that a cylindrical piece of lead is a solid, and therefore can't compress or be compressible. Unless of course it was surrounded all around by something strong like a steel swaging die and pressed into a particular shape.

What I am saying is that with the exception of very soft lead and/or Minie balls, I think lead boolit obturation might just be a myth.

Sounding more and more like a "bait and troll" excercise. Not all that long ago the greatest minds in the world had trouble coming to grips with the concept of kinetic energy. Much later (a couple or three hundred years later) and really fairly recently the same genre of scientific minds had trouble dealing with the relationship between kinetic energy and the impact physics of a high velocity, low mass object. An even simpler concept is obturation as it pertains to the discussion here. The lead bullet, a plastic body. :coffee:

[454PB]

I had to vote no.

They can only obturate if one of the critical measurements isn't correct.

OK, this is about the line of discussion I expected. Boolits can't obturate if there is no room to "bump up".

Now, as a test let's use a section of rifled barrel as a sizing die. It's groove diameter is .451". I now drop a .452" boolit into it's "mouth" then place the die center punch on the boolit base, and proceed to pound on it with a 3 pound ballpeen hammer. When it exits the die, what will in measure?

What if you place the die on a steel plate and continue to pound on the center punch? Will it bump up?

Sure, if this same .452" boolit is fitted in a cartridge case and a chamber that is oversized, it will bump up some as it enters the cylinder throat, to be immediately sized back down as it enter the barrel. But if the chamber and throat is properly sized, it won't allow it to bump up, the same as the example above.

So.....can they obturate? Yes, if they are undersized to start with. Do they obturate? Not necessarily.

[Marlin Hunter]

But hay you come on up here and live with little daylight and temps in the -30's and see if you don't get snarky.

BIC/BS



I'll trade you 5 million liberal commies for your -30's and little daylight.

:mrgreen:

[geargnasher]

Russel, would you please give us your own exact definition of "Obturate"?

I just want to make sure that we don't have confusion about it here because many people use it to mean "bump-up" or "enlarge" when actually I understand it do refer ONLY to the state of SEAL achieved, by whatever means, at any point of boolit/barrel interface.

Boolits don't obturate to fit the bore. Obturation is what happens when a bullet seals the gases in the bore.

Thus, it should be said that "obturation of expanding gases from the powder combustion is achieved in the bore by the boolit's ability to conform/bump-up/enlarge/swage/flow/etc."

We had a pretty long and heated thread about this awhile back, I think it boiled down to a simple matter of rhetoric.

If I'm wrong in my definition, someone please correct me.

BTW, I voted affirmative because obturation occurs in all my guns that don't have gas-cutting and resulting leading. I thank JimInPHX for his extensive development of the mulch trap and examination of many of my own fired boolits to determine that not only do bullets tend to swell to fit a bore (if they are undersized and soft enough) but the noses can slump like crazy if launched too hard and the alloy too weak and nose unsupported.

.357 Maximum said it best: I dont' believe it, I know it. This ain't a religion, faith has nothing to do with it.
Gear

[Marlin Hunter]

OK, this is about the line of discussion I expected. Boolits can't obturate if there is no room to "bump up".



So.....can they obturate? Yes, if they are undersized to start with. Do they obturate? Not necessarily.


They will always obturate, although you might not be able to measure it. Take 0.001 inch and keep cutting it in half. When you get to 0 (zero) let me know. Even if the boolit only expands 0.00000000000000000000000001 inch, it still expands. The barrel is also trying to expand (get bigger), between the breech and the boolit, from the same expanding gases that are pushing the boolit forward. Then you also have the barrel trying to stretch because the gases are pushing the breech back, and the boolit is pushing the front of the barrel forward. And you also have the boolit trying to rotate the barrel at the same time the barrel is trying to rotate the boolit. 3 things happening at the same time with the barrel: it's moving all over the place. Thing of a drunk, retarded pimp trying to walk.

[Bullshop Junior]

The answer is yes, and that is all there is to it.

[7of7]

Deliverator wrote:



No, it is not.

A lead boolit contained along its length by a steel bore or barrel has no where else to expand to. It can only travel out the bore, in one direction.

A flying bullet striking a steel plate is not really contained by anything.


Here you have adequately stated yourself that there is bullet obturation. Obturation is more a condition of the bore, than the bullet. The bullet expands to completely fill the bore, and the bore becomes obturated. As a result of this obturation, no gas leaks around the bullet, so leading doesn't happen unless the bullet is of sufficient hardness that the pressure will not deform the bullet enough to cause complete obturation of the barrel, so propellent gasses can escape around the bullet melting a microscopic layer of lead only to leave it in the bore.

Bullet obturation is a myth, however, obturation of the bore by the bullet, as a result of expansion of the bullet is not. Obturation is the same as obstruction, you cannot obstruct a bullet, you can obstruct or obturate a bore...

[felix]

Impossible to get a case stuck with an overload if there is no obturation. A stuck case means the barrel/cylinder expanded and collapsed (did not exceed the elastic limit) trapping the case that expanded and DID NOT contract (enough) because the elastic limit of the case WAS exceeded. Tight necks will not let gas escape around the boolit before the boolit expands. Tight necks are what really is desired, especially with boolits, but also provides no escape room for pressure that might be excessive. Loading books cannot be followed for guns having a tight neck, be the gun a pistol or rifle. A tight neck is not a tight cylinder exit hole, but is the area where the boolit resides in the case before firing. ... felix

Yes, obturation is the act of making an obstruction. The projectile expands to perform an obturation. The word obdurate/obduration is something else entirely and has nothing to do with us. "D" versus "T". ... felix

[John Boy]

What I am saying is that with the exception of very soft lead and/or Minie balls, I think lead boolit obturation might just be a myth.
Russel, you are hypothesizing incorrectly about a subject that has been studied by renowned individuals that were skilled in ballistics going back into the 1800's, Dr Mann being one in the US and many in the UK such as Halford, Metford, Greener and others. And proven by them that obturation of lead bullets is a fact

In current times, you might want to read this short article on the subject by Glen E. Fryxell ... http://www.sixguns.com/crew/obturation.htm

So, why are you trying to disprove a subject that has been studied for decades when you have not done any research on the subject yourself?

Or is this your way of starting a thread just to see how many views and posts you can generate because your statement based on internal ballistics is a indication of stupidity

[JD Yellowhammer]

We can go back further than the 1800's. Check out Sir Isaac Newton, the First Law of Motion, and "inertia." I know which way Newton would vote in this poll....

[Marlin Hunter]

Sounding more and more like a "bait and troll" excercise.


405, in your post #55, you have me listed as the one who made the quote. I did not write that, Russel did. If you go back to post #10 on page 1, you can see that I wrote what was in the quote box, unfortunatly the board sofware does not transfer the quote.

here is what I wrote that russel responded to.

the rear wants to go faster than the front, so it would distort or compress the lead a little to make it expand.

[405]

MarlinJ, Sorry, it was not pointed at your quote. This too is only in response to Mr. Nash's posts/replies throughout the thread. After listing his education I almost got more "snarky" than Bullshop. Decided to just leave it to the imagination about past and recent past "scientific" minds. Even the most basic high school physics class would teach about kinetic energy, inertia, acceleration, momentum, states of matter, compressiblity, etc. Mr. Nash made it a point to cite his education and then got off on the liquid, solid, gas, plasma tangent.... kinda like a scissors, rock, paper level of discussion. As far as internal ballistics and obturation of a "solid" object in a bore (context of this discussion).... of course a solid is NOT compressible nor is a liquid for that matter... but obturation is not about compression... it IS about deformation of a solid "plastic" object... the bullet. With some exceptions, obturation has more to do with inertia and acceleration than with kinetic energy but the ke analogies in other posts are OK and similar enough.

All this reminds me of the movie "Space Cowboys" where the MIT grad, weeny astronaut cites his education yet has some trouble with a concept. Clint Eastwood turns to him and says something like, "maybe you oughta get your money back". :)

[stubshaft]

MarlinJ,
All this reminds me of the movie "Space Cowboys" where the MIT grad, weeny astronaut cites his education yet has some trouble with a concept. Clint Eastwood turns to him and says something like, "maybe you oughta get your money back". :)


Very well put 405.:lovebooli

[Russel Nash]

405 wrote:


MarlinJ, Sorry, it was not pointed at your quote. This too is only in response to Mr. Nash's posts/replies throughout the thread. After listing his education I almost got more "snarky" than Bullshop. Decided to just leave it to the imagination about past and recent past "scientific" minds. Even the most basic high school physics class would teach about kinetic energy, inertia, acceleration, momentum, states of matter, compressiblity, etc. Mr. Nash made it a point to cite his education and then got off on the liquid, solid, gas, plasma tangent.... kinda like a scissors, rock, paper level of discussion. As far as internal ballistics and obturation of a "solid" object in a bore (context of this discussion).... of course a solid is NOT compressible nor is a liquid for that matter... but obturation is not about compression... it IS about deformation of a solid "plastic" object... the bullet. With some exceptions, obturation has more to do with inertia and acceleration than with kinetic energy but the ke analogies in other posts are OK and similar enough.

All this reminds me of the movie "Space Cowboys" where the MIT grad, weeny astronaut cites his education yet has some trouble with a concept. Clint Eastwood turns to him and says something like, "maybe you oughta get your money back".


Did I really come in here and cite my educational background as in a "ha ha, my poop don't stink and ya'll are dumber than a box of rocks?"

Did I really put it that way?

If I came across that way, then my apologies. I am sorry.

What we are discussing is a very interesting metallurgical phenomenon that occurs in a split second.

The technology wasn't around in 1909 like it is today to be able to measure chamber pressure and velocity.

If it seemed to you all that I was stuck on the very definition of "compress" or "compression", again, my apologies. Whole scientific discoveries or research are based upon how certain words are operationally defined.

If you will look through this thread here one more time in one of my posts I wrote:


I never did say that lead was NOT malleable.

Which is, in my opinion, different from being compressible.

This thread has been educational in several ways.

I thanks thee for that.

[357maximum]

When I learned about solids/liquids/gases my professor actually had one caveat about compressible liquids.....

His words "liquids are actually slightly compressible, but we will call them un-compressible for the ease of keeping the equations somewhat sane"

I personally feel (no data to back it up...just a gut feeling thing) that some solids are also a teeny tiny bit compressible but the scientific minds of the day are alot better with their delivery of the facts and then arguing the facts/points than I ever will be. For me to do so would be like starting a gunfight with a dull popsicle stick while screaming the earth is flat and some politicians have our best interests at heart.

Doing such a thing would make as much sense as wiping your bottom before you do your bussiness

Seeing as how my personal trolling exercises normally involve a 21ft starcraft islander/ some downriggers and flutter spoons on the great lakes for trout/salmon....we will leave that one alone eh.

Besides as 405 states...we are talking about about deformation not compressibility..............good form 405.

[Marlin Hunter]

What we are discussing is a very interesting metallurgical phenomenon that occurs in a split second.

The technology wasn't around in 1909 like it is today to be able to measure chamber pressure and velocity.

...

This thread has been educational in several ways.

I thanks thee for that.


The two methods of checking chamber pressure work because metal obturates or deforms. The copper crusher is one example, and the piezo electric stress-strain gauge is the other one. To prove a solid can be compresses, take a long pipe or bar, hold it horizontally with only one end being supported. You will notice the bar bends down do to gravity. The bottom half of the bar is under compression and the top half is under tension. Forgings are also proof that solids can be compressed.

[Russel Nash]

Just an FYI...

I remembered back to my time making stained glassed windows.

The very soft lead came has to be stretched before it can used to construct what is essentially a glass jigsaw puzzle.

So... I have kinda changed my mind about the obturation thing, especially with rifle bullets. Esepcially after see'ing John Boy's picture in my other thread.

If I can just stretch lead by hand with a pair of pliers on one end, while the other end is held in a vise, then YEAH! it is now NOT hard for me to imagine that a lead alloy boolit squishes down when being accelerated from zero to 2,000 feet per second plus plus in the distance of about 20 inches.

And for whatever it is worth to you, I did picture the use of copper plates used in shaped charges...say like in the case of the Deutsche bank president's assassination. IIRC, TNT was used as the "propellant" in that instance. IIRC, TNT burns at something like 14,000 feet per second, so the copper plate folded in half very plastic like and flew at about 10,000 feet per second right through the Deutsche bank president's armored car, and killed him. Leaving his two bodyguards and driver without a scratch.

Anywhoo...again, putting something into compression is different than compressing a gas

Those little piezo electric "transducers" wouldn't work if metal didn't contract and expand.

Thanks again for all your replies.

[felix]

John 20:29 ... felix

[wallenba]

With all variables being equal except the BHN, there must logically be a hardness where it stops obturating. Question is, I guess, is it within the sphere of our uses in casting boolits?

[John Boy]

The technology wasn't around in 1909 like it is today to be able to measure chamber pressure and velocity.
Felix, you are so right but in plain English, this guy doesn't know the difference between S*** and Shinola!

Reference Sources:
1813 - Birmingham Gun Barrel Proof House tests
1841 - William Greener book
1841 - Colthurst copper plate tests
1830 era - Hutton and Robins experiments
1878 - Metford article, written for the New York Spirit of the Times
1888 - Halford book
1889 - C&H's Notes on Shooting (shotgun specific)
** Winchester and UMC caliber specific data by calibers, published in their catalogs before 1909
** Cartridges of the World, ALL Obsolete Calibers developed before 1909 - specific data, including published factory loads
And for good measure ...
Greener, Gunnery in 1858: being a treatise on rifles, cannon, and sporting arms

How can it be that these historical sources made specific determinations how to measure chamber pressure and velocity prior to 1909?

So, Mr Nash - You Prove You are Correct and I am Wrong!
Be sure to post it for all to see
Otherwise, put a plug on your statements that don't hold water and start doing your homework before quoting what you deem to be facts

[felix]

Obturation would stop its rapid climb when the static foward resistance of the projectile is broken allowing the projectile to move. Yes, depends on mass (weight), projectile and barrel hardness, and how tight the projectile had already plugged up the barrel. ... felix

Yeah, maybe a better definition of obturate would be "to plug up" rather than "to close up" or is it "down or sideways". I bet the word was defined in Roman times as the methodology of stopping water leaks, be they in boats or aquaducts. ... felix

[hoosierlogger]

http://i667.photobucket.com/albums/vv35/malady_rising/train-wreck.jpg

[lwknight]

This thread came to the end of its perverbial road. The course has been ran.

[Russel Nash]

Russel Nash (that's me!) wrote:


If I can just stretch lead by hand with a pair of pliers on one end, while the other end is held in a vise, then YEAH! it is now NOT hard for me to imagine that a lead alloy boolit squishes down when being accelerated from zero to 2,000 feet per second plus plus in the distance of about 20 inches.


Thanks for all the courteous replies everybody.

[swheeler]

Thought I would post the definition of the word, obturation as found in a reloading manual, since that is what we do, reload.

OBTURATION; shortening and expansion of a bullet in the bore in proportion to the pressure exerted on it by gas pressure. Enjoy

[303Guy]

1. gases
2. liquids
3. solids
4. plasma

Also, in those classes, I learned that of the first 3, only the gases are compressible. Solids and liquids cand be compressed elastically. Solids can be compressed into a higher density sate. Gasses on the other hand need to be contained - that's what is meant by 'compressible'. Metals have properties like ductility, malleability and elasticity. The latter two properties will allow for obturation in a bore. Permanent obturation would be due to malleability.

[lwknight]

What happend when enriched plutonium is compressed into a denser state? LOL

[John Boy]

Well, looks like the 94.7% who voted Yes that lead bullets obturate have a handle on the tea cup :mrgreen:
What I'd like to know is ... why the 6 voted No?
So as the curtain slowly closes on this thread ... "GOOD NIGHT, Mrs. Calabash--wherever you are!"

[Russel Nash]

303 wrote:


Solids and liquids cand be compressed elastically. Solids can be compressed into a higher density sate. Gasses on the other hand need to be contained - that's what is meant by 'compressible'. Metals have properties like ductility, malleability and elasticity. The latter two properties will allow for obturation in a bore. Permanent obturation would be due to malleability.


Thanks for that most cogent and non-smart a$$ey reply.

Maybe a better word instead of obturation should be deformation or "upsetting".

As in it would be possible for a lead projectile to upset or deform but not necessarily obturate the bore. And obviously there are various degrees of obturation.

As far as density goes, it would be kinda difficult to measure at home the density of a fired and recovered bullet versus that of an unfired boolit.

Said another way, I think a fired boolit does not necessarily become more dense.

I think.... (where density = mass/volume)

[runfiverun]

it cannot become more dense as it has no place to get more mass from.
when i said compressed i meant pushed from one direction the front is not moving just yet but the rear is. what happened to the metal if some is moving and some aint it either goes sideways [not compression] or it compresses [swages] maybe it's just squeezing out the air. [and all boolits have some air in them no matter what we think about our casting abilities.]
if we are squeezing out the air we are compressing the alloy in its solid state.
i ain't no scientist it's just how i picture things in my head.
to me compression is squeezing,just like in an internal combustion engine.

[Marlin Hunter]

John 20:29 ... felix

I had to look that up.

This website has many interesting translations of the same bible

http://bible.cc/john/20-29.htm

[Marlin Hunter]

it cannot become more dense as it has no place to get more mass from.



It doesn't have to gain more mass.

Density = Mass/volume

Change either Mass or Volume and the Density changes.

[Green_Canoe]

In my scan of the responses I saw no mention of inertia. Inertia is the key to the bullet upsetting to fill the diameter of the bore.

I doubt anyone would disagree a lead cylinder when placed between the jaws of a vise and compressed between those jaws will get shorter. When the cylinder gets shorter the material is displaced radially causing the cylinder to grow in diameter.

The effect is the same in the barrel of a gun. One jaw of the vise is the pressure caused by the burning gunpowder. The other jaw of the vice is the inertia of the bullet resisting acceleration. The bullet is shortened and the displaced material causes the bullet to grow radially until that growth is stopped by the barrel wall.

This process can be prevented by sellecting a lead alloy that has a high enough compressive strength that the forces imposed by firing the bullet do not exceed the elastic strength of the lead alloy.

[Maven]

"Solids aren't compressible, like a block of steel. So my thoughts are that a cylindrical piece of lead is a solid, and therefore can't compress or be compressible. Unless of course it was surrounded all around by something strong like a steel swaging die and pressed into a particular shape."

A few ideas that I need explained: If solids aren't compressible, how does one explain the prior use of copper/Cu alloy pellets in CUP (pressure) tests of powder and bullet loads? Also, when bullets are swaged, isn't the solid material compressed? I remember Dave Corbin saying essentially that if you can develop enough pressure, you can swage (reform) just about anything (figuratively). Since these are both empirically true, the question to be asked is, "How likely is it that a bullet (solid Pb, Cu, jacketed) WON'T expand (obturate) under given pressure conditions?" Further, shouldn't obturation be proportional to the mass, acceleration and ductility of the projectile?

[Russel Nash]

Green Canue wrote:


In my scan of the responses I saw no mention of inertia. Inertia is the key to the bullet upsetting to fill the diameter of the bore.

I doubt anyone would disagree a lead cylinder when placed between the jaws of a vise and compressed between those jaws will get shorter. When the cylinder gets shorter the material is displaced radially causing the cylinder to grow in diameter.

The effect is the same in the barrel of a gun. One jaw of the vise is the pressure caused by the burning gunpowder. The other jaw of the vice is the inertia of the bullet resisting acceleration. The bullet is shortened and the displaced material causes the bullet to grow radially until that growth is stopped by the barrel wall.

This process can be prevented by sellecting a lead alloy that has a high enough compressive strength that the forces imposed by firing the bullet do not exceed the elastic strength of the lead alloy.

Exactly!

[Russel Nash]

@ Maven....

http://www.smoothharold.com/wp-content/uploads/2008/12/facepalm.gif

Ahhh...jeesh...

There is a difference between a gas that is compressible vs. a solid that is better described as malleable or deformible.

[Russel Nash]

FYI....

http://www.chem.purdue.edu/gchelp/liquids/character.html

[Maven]

What's the difference between compressible solids and malleable and/or deformable ones, or is this merely semantic?
I meant to include this in my earlier post, but forgot: Ken Mollohan (Molly here) wrote in a recent "Fouling Shot," that while CB's obturdate, they don't expand to as great a degree as we think. However, they are solids and they do obturate, if only to a slight degree.

[Russel Nash]

You didn't click on the link, did you?

That was from Purdue University, I think, it is pretty much the norm or standard as far as what liquids, gases, and solids do.

Compressible in my opinion is that the volume changes and consequently so does the density, since you are packing the same amount of mass into less space. As in you probably have an air compressor in your shop or garage. However, I doubt that you have a liquids compressor or a solids compressor too.

A soft lead boolit deforms much like squishing a marshmallow between your thumb and index finger. Its shape changes, but its volume does not.

[lwknight]

I still say that solids are compressable. Try it with plutonium. Ask Hiroshima, Japan about it.

[Frozone]

I still say that solids are compressable. Try it with plutonium. Ask Hiroshima, Japan about it.

Actually it was Nagasaki, they used the Uranium gun bomb on Hiroshima.

Compressiblity implies a change in density and volume (see Boyle's law, although it applies to a gas).
Lead has no change in volume with pressure (at least real world pressure), which is Exactly why it obturates.

Nash: Great troll by the way!!!

[tonyb]

@ Maven....

http://www.smoothharold.com/wp-content/uploads/2008/12/facepalm.gif



No.1 I just messed my diaper.

[AriM]

Marlin Hunter wrote:



And that my friends is what brought me to start a poll here.

From my high school and college physics/chemistry classes, there are only four states of matter:

1. gases
2. liquids
3. solids
4. plasma

Also, in those classes, I learned that of the first 3, only the gases are compressible. Liquids are not compressible, and that explains why hydraulic pistons work on something like a crane or a back-hoe. And why they don't use pneumatic rams or pistons for some stuff. Solids aren't compressible, like a block of steel. So my thoughts are that a cylindrical piece of lead is a solid, and therefore can't compress or be compressible. Unless of course it was surrounded all around by something strong like a steel swaging die and pressed into a particular shape.

What I am saying is that with the exception of very soft lead and/or Minie balls, I think lead boolit obturation might just be a myth.



woah woah woah!!! liquids not compressible...??


http://scienceworld.wolfram.com/physics/Navier-StokesEquations.html

http://en.wikipedia.org/wiki/Incompressible_flow

please read the content in BOTH links....ALL materials are compressible.....but in standards based equations we must say that they are NOT, so that a number can be plugged in, and a result reached....by the way I voted Yes....it's my opinion, that if a boolit needs to fill a space it will obturate.....if the boolit already fits the space tightly (which is impossible, unless the rifling grooves were pre-molded into the projetile, within a perfect tolerance) then it will elongate...lead is softer than steel and the rapid expansion of gasses and high pressure spike, should cause the projectile to

1. obturate and fill all voids (and shorten)
2. lengthen due to pressure and uneven heating

I suppose this is just fuel for the fire, but this is simple flow dynamics...if you can't figure out the formulas in the links, it's not important....the results and explanations are all that matter....

ALL materials deform and compress/expand according to pressure....ergo heat


this is another example of people thinking that a + b = c, then c must always equal a + b

it's far too simple to say that one of these things is ALWAYS true....it will depend on pressure, temperature, flow, and hardness....and about a zillion variables than NO ONE here is qualified to measure....

[Maven]

Read the link since I didn't see it earlier. However, they do say "not EASILY compressible," which isn't the same as NOT compressible. Another question and an observation, does obturation (of a bullet) necessarily mean a change in volume as well? Will you enlighten me please? As for the observation, what's the point of the Star Trek image? That I just don't get it? Who's being snide (snarky) now?

[BeeMan]

Nash,

To get an appreciation of lead in the solid state flowing under pressure, you need to see the core extrusion presses at a bullet manufacturer. It's all plastic flow when you exceed the yield strength of the material that is being subjected to pressure.

Hornady turns 260 lb billets of lead several inches in diameter and a couple feet long into spools or core material for jacketed bullets. It takes a fair amount of lead to crank out a couple million bullets a day. They cast the 260 lb billets in house - you should also see the casting pots and billet molds.

BeeMan

[felix]

Everything is compressible, Maven. That's how "they" came up with the idea of the "black hole" being a reality. Obviously, it does not mean that a black hole exists for real unless religiously spoken as such. Obturation does not mean a permanent deformation of anything, projectile or container. ... felix

[Edubya]

Gawd! I use to work for a fella that would ask you a question like, "Do you believe that cast lead boolits obturate (swell up) upon firing?" Then would continue to try to counter you for so long until you didn't even remember where it all started. All of a sudden he would would act as if he knew the correct response the whole time! He had finally absorbed all of the explanations and repeat what yu had told him from the beginning!
Next thing that you knew, he was spouting off his knowledge about the subject as if he was the original thinker.
I learned his trick after a couple of times and would just say; "I dunno." or "Whatever."
EW

[runfiverun]

marlin hunter.
you got my point.
you can change the volumn and the shape [wait that would be bumping up or sumthin]
errr smashing down, sept it's already smaller so i guess it gets larger around yet shorter.
except that we already been told it don't.
so even when it does it don't even if it is,then i guess it still ain't.
maybe the superlube flows outwards and upwards and jumpa ahead and covers the entire bore before the boolit gets there making the bbl .003 smaller so the too small boolit now fits or whatever.

[Russel Nash]

^^^ well, that depends...

http://www.memorial-walls.com/abbott_and_costello_whos_on_first.jpg

Who's on first?

[muzzleblast]

For what it's worth,

When I pull the trigger on my .357 magnum the bullet is instanteously subjected to the following (in round numbers):

35,000 pounds per square inch pressure,
Acting on 0.10 square inch,
With a resultant force of 3500 pounds,
Linear acceleration of the bullet goes from zero to 900 miles per hour (1300 feet per second),
And rotational acceleration goes from zero to 67,000 revolutions per minute (1:14" twist).

Since lead is malleable (i.e. capable of being shaped or formed, as by hammering or pressure), it "obturates" or "swells up" as a result of the compressive, and to a lessor degree rotational, forces associated with being fired down the barrel of a gun; resulting in deformation (i.e. a change in the shape or size of an object due to an applied force) and specifically in the case of a lead bullet, plastic deformation (i.e. permanent deformation).

Kind of a long way of agreeing with what Bullshop and others have said relative to undersized bullets "bumping up" in oversize bores.

[Eutectic]

I voted yes..... and so did Webster... But he couldn't get signed in!

Eutectic

http://www.hunt101.com/data/500/obturate.jpg

[RobS]

Yep it does and I responed by giving an example on the other thread title " Regardless of your opinions on obturation, have you investigated it for yourself?"

http://castboolits.gunloads.com/showthread.php?t=71578

[Storydude]

Don't forget the Mass of the Bullet is acting against the Forces pushing on the rear of the bullet.(Newtonian Physics)IF the forces on the rear of the bullet exceed the Modulus of Elasticity of the bullet, said bullet will deform until restrained by the bore. At that point no more energy can be used for displacing the bullet metal and all forces go towards acceleration.

[w30wcf]

For anyone who thinks a lead bullet can't obturate, do this simple test.

Fire a .22 L.R. cartridge into some medium and recover the bullet. The bullet, before firing, had an undersized heel. After ignition, no heel. It has increased to the diameter of the firearm's groove / bore diameter.

w30wcf

[mtgrs737]

I haven't read all the posts so I'm sure someone has already said this: Solids may not compress but they certainly do "Flow" given enough pressure. Hit with many thousands of pounds of gas pressure the base of a lead boolit will flow into any void it can find.

[Idaho Sharpshooter]

Ever seen the pictures of Colt's Fitzgerald's shooting his New Service Colt with no barrel? The slugs were caught in a pool and had obdurated enough to actually show signs of the receiver threads where the barrel would have screwed in. They had expanded to over .90 caliber, lopsided of course.

Rich

[Bullshop]

I have that book , Shooting By Fitz. Maybe I can get someone here to scan it and post it. Hello Jr. where are you son.

[JSnover]

What I believe is that the lead really doesn't compress or expand in a properly sized boolit. It gets displaced. Initially the boolit gets shorter and fatter as the base crashes into the nose (obturation, swelling, slugging up, bumping...). The lube grooves get smaller as the barrel sizes the driving bands down; displacing some of that lead into the grooves, which displaces some of the lube onto the bore.

[twotrees]

If you have instrumentation good enough, ALL metals compress in 2 ways. Linear deformation and Plastic deformation. Linear deformation is recoverable ( it comes back to the same shape, if pressure is removed). Plastic deformation is when the yield strength has been exceded and it will NOT return to it's original shape.

Take a look at your favorite beverage can. It was deformed Plasticly, to get it into that shape. On the top there is a key that allows you to open it, that key presses on an area that has been further deformed. That area's strength is actualy Higher than the rest of the can, but when you apply pressure (The Key) it tears because it's higher strength, but more brittle nature , from all the deformation it has undergone.

A Boolit even a J-word one fore-shortenes when it is fired, for the stated priniple of the front, trying to stay at rest, while the back is being booted by high pressure gas.

If it elasticly deforms ( stays below the Yield point of the material), then it gets back in shape before it moves very much.

In the case of Cast Boolits, the yield strength is Way below ( Even lino-type) the pressure applied to it's base, so, it would seem that YES it does "Get Bigger in Dia. and shorter in length" , due to being plasticly deformed.

TwoTrees

Worked in Fracture Mechanics for over 37 years.
I brake things and get paid to do it !!!!

[cbrick]

I started following this thread from the begining but it soon got me to thinking of a book I had read many years ago. The last couple of days have been spent re-reading this book.

Do boolits obturate? You betcha they do and not only in the bore, if the barrel is short enough they continue to obturate the base after they leave the muzzle, how much depending on barrel length, powder type & charge, alloy and boolit weight. In some tests the boolit bases actually expanded by 50% of original diameter after it left the muzzle.

Don't believe this? Read The bullets flight by DR. Franklin W. Mann available from Wolfe publishing on CD.

Rick

[Multigunner]

runfiverun wrote:



for the sake and sanity of scientific discussion let's NOT use the word compress when it comes to talking about a solid like a lead boolit.

Ever heard of a work hardened edge on a bronze knife or sword?
Same goes for wought iron swords. Hammering the edge compresses the metal, packing the molecules more tightly together. That way fairly soft metals were made hard enough to take an edge.
The amount of compression is far too small to see or measure, but its there just the same.

As mentioned earlier on the bullet can retain its original volume in space, obturation only requires that it expand in diameter.


Do boolits obturate? You betcha they do and not only in the bore, if the barrel is short enough they continue to obturate the base after they leave the muzzle, how much depending on barrel length, powder type & charge, alloy and boolit weight. In some tests the boolit bases actually expanded by 50% of original diameter after it left the muzzle.

Don't believe this? Read The bullets flight by DR. Franklin W. Mann available from Wolfe publishing on CD.

Rick
Correct, I've examined bullets fired from deringers and short barreled .22 autos, the heel base blown out larger than bore diameter by the muzzle blast.

I find this sort of discussion interesting, because the fact that lead bullets do in fact obturate is obvious to anyone who shoots much at all.

Only if a squib load somehow propelled a vastly undersized bullet down the bore without generating enough pressure to upset the bullet would it be otherwise.

Even a bullet hammered into the rifling by use of a false muzzle will, when fired with a full charge, deform enough to all but wipe out its lube grooves, and expand to make a gas tight fit. You can't get a truly gas tight fit without obturation , even using a false muzzle.

Overcoming the inertia of the bullet deforms the bullet in the only direction open to it, radially.

Heavy lead bullets used for thousand yard match shooting were often swaged from two differing alloys, a soft rear section to obturate fully into the grooves, and a harder front section to resist deformation of the nose of the bullet from the initial shock of discharge. Charges for such a rifle I once fired were 300 grains of black powder with a one thousand grain two piece paper patched bullet.

Years ago there was a turret breech black powder cap and ball .22 rifle marketed for youngsters and small game hunting.
The rifle used a .24 buck shot, oversized for the .22 bore. When fired the oversized ball was compressed into the bore but rather than coming out as a capsule shape rounded at each end it came out as a rounded nosed flat based bullet.
Even though oversized for the bore, like most C&B revolver bullets or screw barrel pocket pistol balls, the bullet still has to upset to maintain a gas tight seal.
If you've slugged many bores you'll know that if you push the oversized slug all the way from the throat to the muzzle with a rod its highly unlikely to maintain full contact with the bore surface and will emerge as a somewhat looser fit than if simply tapped into the rifling and then tapped back out.

If not for building chamber pressure applying enough force to the base of the bullet to continue the upsetting process for the first six to ten inches of bullet travel gas blowby would eat away the surface of a lead bullet before it reached the muzzle.
In bores that were deeply gas eroded this often happened anyway, even with FMJ bullets, resulting in poor accuracy and in extreme cases shed jackets and blown through cores.

PS
From the "Ask a Scientist" site


Question - How come, when most solids are more dense than liquids,
liquids are not compressible, but most solids are?
Both liquids and solids are compressible -- only slightly, but
compressible nonetheless. The compressibility of solids is generally smaller
(they resist deformation more, because compressibility is defined with an
explicit negative sign) than for liquids by ~ 3X. However, there is overlap
because other factors are also important.

The compressibility: K = -(dV/dP)/V

varies with temperature, pressure, and other variables, so it
is quite difficult to measure. The compressibility of solids, especially
single crystals, is even more complicated. Assume the atoms in a crystal
have coordinates (x,y,z). The crystal structure is often not isotropic, i.e.
the arrangement of atoms/molecules in the 'x', 'y', and 'z' directions is
not the same. So an increase in pressure in the 'x' direction results in a
DIFFERENT change in volume in the 'y' and 'z' directions. The same is true
for the other coordinates. So the compressibility now has NINE components --
Kij where both 'i' and 'j' can equal 'x', 'y', and 'z' -- i.e. components
Kxx, Kxy, Kyx,..., Kzz. The term Kxy, for example, measures how the
dimensional change in the 'y' direction if I squeeze in the 'x' direction.
For some crystals Kxy may not even equal Kyx!! Such nine component arrays
are called "tensors" and they have a whole "algebra" that governs their
mathematical behavior.

Vince Calder
================================================== ============
Liquids are compressible. They just do not compress much compared to gases.

Richard E. Barrans Jr., Ph.D.
Director of Academic Programs
PG Research Foundation, Darien, Illinois
================================================== ============



Thats why they say liquids and solids are "Virtually incompressible" rather than truly incompressible.
You may not be able to get a clear picture of how much a solid can compress, but it happens.

[felix]

"That's why they say liquids and solids are "Virtually incompressible" rather than truly incompressible.
You may not be able to get a clear picture of how much a solid can compress, but it happens. "

EVERYTHING compresses and that is the reason folks decided there is a such thing as a Black Hole definition for those thingies they see (don't see, actually, but they see the tornado like swirls into the center) via the Hubble. Short of that, everything expands and contracts and therefore can be considered something alive as opposed to being dead, i.e., having entered into the black hole. ... felix

[Eutectic]

On the comment that solids are not compressible...

Applied to the "title" of this forum..... "Cast Boolits"

The best of our lead/lead alloy castings have some porosity. Then too, grain structure may be in a pattern somewhat shy of maximum density....

Upon firing above the "yield" of our alloy then; the boolit does compress to higher density!

If said boolit is contained (as in the barrel) maybe compression stops... But who's to say some "stubborn" crystals defy change until above our max working pressure?

Eutectic

[Lee]

No mind the physicists and theoretical, tho they are right. Practical experience with a hydrostatic pressure vessel is all you need to see that water(a liquid) is compressible. We used the back end of a 16" naval gun, cut and plugged. At +40,000 psi about 3 gallons more water could be forced into the beast. There was a steel tape around the outside circumference. Taking into account the "swelling" of the barrel at that pressure, there was still about 3 gallons MORE water forced into the barrel. And it wasn't leaking. Yearly, the staties came into town to measure the diameter at pressure(insurance/safety/licensing/etc). The barrel would expand a few thousands of an inch in diameter at pressure.
Those barrels are not one piece, rather a series of concentric tubes (interference?) fitted together. After several years of cycling to pressure, the end would telescope out, revealing the distinct layers. Even that was taken into account, and the 3 gallons is real. If you go to the Lee Reloading webpage, you can see a picture of the naval gun in question, they use the picture to explain their "new" breech lock die. Interesting.
The controls on the cannon are placed so that basically the seaman has to position his body out of the way to actuate the lifting/lowering mechanism for the breech(weighs about 4000# if I remember correctly??)
Sorry if this is thread drift, just some memorable moments I have had the privelege of experiencing.
P.S. you should see how a sealed can of pop reacted to being hydrostatically compressed. Usually came out looking like a smaller version of a 12oz can, perfectly formed, just smaller. A 4" x 4" x 6" piece of balsa wood would come out looking like a long toothpick.....Lee

[felix]

Expert stuff, Lee. Thanks for the post. ... felix

[Lee]

I neglected to mention that also, yearly, one of the smaller, less claustrophobic employees would be enjoined to lay on the carriage, be pushed into the barrel, and inspect for any nicks or scratches that could become stress riser points. He would use a die grinder to radius out any found imperfections.
Something you couldn't get me to do for a $1,000,000....................:)

[felix]

What would be interesting for further "research" would be to shock the water in the barrel with various frequencies and amplitudes until a SEE condition was reached. ... felix

[Multigunner]

I neglected to mention that also, yearly, one of the smaller, less claustrophobic employees would be enjoined to lay on the carriage, be pushed into the barrel, and inspect for any nicks or scratches that could become stress riser points. He would use a die grinder to radius out any found imperfections.
Something you couldn't get me to do for a $1,000,000....................:)

There are, or were at any rate, two huge muzzle loaded coastal defence guns on Gibraltar.
When one gun misfired for some inexplicable reason and the charge had to be pulled, they found the equipment available for reattaching the cable used to lower the shell in place just didn't work.
A very small British sailor volunteered to crawl down the bore of the loaded gun and hook up the nose cap ring of the shell to the cable's hooked end by hand. He was actually given a medal for this.

Not sure if the guns are still there, I've only seen photos that accompanied the article.

PS
This does remind me that we can't really see what goes on inside the bore in real time, and until flouroscopes and high speed photography everything accepted as fact about internal ballistics was arrived at by studying the after effects of the shot.

There was a pretty good article about what happens when a gun is fired, I found it on the net a couple of years back. There were a few things in the article I found suprising.

[GSM]

Gold stars to those that mentioned plastic properties / behavior of "solids".

[Willbird]

I have not ever measured bullets lengths before and after firing, it would not be terribly difficult to measure to the .0001. I'll file that away for something to do one day.

I DO know that a remington 158 grain .357 dia hollow point gets shorter when you fire it from a 357 maximum, the nose swages out big enough that the bare lead rubs on the rifling..which is a .03: or so increase in dia in that area.

I know that from catching the bullets in polyester fiber fill, which wraps around the bullet and forms a sort of snowball. Those bullets were too hot to hold after firing too. Also the lyman 12 gauge slug that looks like a big airgun pellet collapses down into something that looks completely unlike what it started out as, and it gets hot as hell doing that. I saw some of those same slugs that people pulled from dead deer and they looked just like mine fire into fiber fill.

I decided to try the fiber fill because supposedly ballistics experimenters in the early days used "cotton waste" for the same thing, well I had no cotton waste, but I DID have fiber fill. I packed a steel pipe about 8" in dia with the contents of 2-3 bags of fiber fill, it would stop the 357 maximum bullets and the 12 gauge slugs just fine. The "snowballs" did hit the steel plate I had at the back end with a pretty good thump.

[AriM]

Gold stars to those that mentioned plastic properties / behavior of "solids".



;-) :castmine:

[pls1911]

Gentlemen,
Please go google/read up on plastic displacement of metallic alloys and elastic deformation limits of metal.

Think kid tricks...
Plastic deformation:
1. hammer a lead bullet
2. hammer one side of a steel or copper strip to make a flat "bend"
3. retrieve a 16 penny nail after it's run over by a train.
4. think of hammer forged steel parts (BIG hammers make great parts!)
Lead in it's solid state exhibits the same characteristics.

Elastic limitations:
1. pull small wire spring outward a little it spings back ( it was deformed within it's elastic limits)
2. Pull the same spring WAY out like a straight wire, and it won't return as a spring. (It was deformed beyond it's elastic limit)
Lead in it's solid state exhibits the same characteristics. (Yes, you can make a weak spring of lead wire for demonstration, but it's useless from a practical application.)

All of these pieces retain their original material and weight but are different shapes via plastic displacement or deformation beyond the material's limit of elasticity... high school physics and materials science.

The "hammer force" of chamber pressure does the same thing to the butt of the bullet. The degree of displacement is dependent upon the hardness of the alloy, the amount of pressure, and of course the constraint of chamber size.

The simple answer is YES!!! Bullets can obturate, most do obturate within the constraints listed above.

I just size/check and lube .30 cal through a .312 die and go shoot....pre 1950 marlins, winchesters, savages, remingtons and mil surp misc...30-30, 308, 30-06.... Don't waste your time distracted with obturation.
Just slug you barrel, cast ww or softer mix at .001 to .002 larger, heat treat, lube, check, load and shoot.
As a practical matter, unless you have some really weird barrel or bullet dimensions, you'll be fine.

[alamogunr]

There is an article in Precision Shooting's February issue(the one with the snake on the cover) by M.L. McPherson("Revolver versus Rifle: Chamber Pressure") that may help some with the understanding of the subject of this thread. About all I can do is refer you to the article. I don't know where it may be found except in the printed issue.

I hope those with more technical expertise than I have will be able to access the article and comment.

John
W.TN

[felix]

Thanks for pointing that out. I read the article. The appearance is good in that magazine because it lets the BR crowd in on what we have been discussing for quite a while now. BR folks typically don't care about pressure per se, just as long as the bullet reaches the target before the ambient changes from what was sighted for. Their guns simply idle at 65K psi making the weak link the cartridge case. Their cases are junked after about 10 shots, and their barrels after about 750 shots. The major expense of that sport deals with travel ramifications.

It seems the author was using our info too. He misuses the word "obturate" like we do, and he confuses the meaning of toughness and hardness like we do.

It would have been more interesting had the article went into different powder types and speeds. There are several combinations which would show the opposite characteristics from my experience. If the powder is intentionally oxygen starved up front of the burn as per deterrent application, that powder will increase pressure beyond "normal" once the tail of the projectile passed an opening, like between the cylinder and barrel. Powders that typically show a BRILLIANT flame at night are those which can be classified as such.

... felix

[wizard93]

I don't know how obturation works in some guns and not in others, but apparently that's the case. Several years ago, I started loading 40-82 WCF ammo for my wife's uncle who owns an 1886 Winchester. After some research, I learned to cast the bullets using my "soft" alloy instead of the WW alloy. In the design of the 40-82, the bullet diameter is .406", but the barrel diameter is .408". This means the bullet has to obturate .002" before it can engage the rifling. One of my theories on this may be due to the fact that it's a lever-action chambered in a black-powder cartridge, it helps aid in chambering the next round easier due to the fouling in the chamber/barrel from the previous rounds fired. Just a guess, though, but all the information I found indicates that the cartridge was designed for an undersized bullet.

wizard93

[Molly]

Marlin Hunter wrote:
So my thoughts are that a cylindrical piece of lead is a solid, and therefore can't compress or be compressible.
What I am saying is that with the exception of very soft lead and/or Minie balls, I think lead boolit obturation might just be a myth.

No, but lead can be spread out like a patty of butter. Just look at the pictures in Mann's book.

Trouble is, Mann's distorted bases could not possibly have been obtained while the bullet was within the bore, because they are larger than the bore. They had to be upset after the bullet had exited the muzzle. Mann's conclusion of massive upsetting in the rifle throat cannot possibly be correct.

I have recovered a huge number of cast bullets from high velocity loads. Alloys ranged from plain air cooled wheelweights to aged and hardened linotype. Some of the loads exceeded 3000 fps, if reloading manuals are to be believed. A very few bases managed to upset enough to leave a faint ring at the top of the gas check. The vast majority had no measurable increase in the diameter of the gas check shank, as measured at the bottom of the first driving band, and perpendicular to the mold lines. Listen carefully: No change in diameter means no upset occurred. Period. Also, I do not recall ever seeing the frosting that occurs at the surface of deformed lead alloys due to dendrite upsetting. No dendritic frosting means no upsetting. Period.

(For those who may not know, dendrites are metallic crystals of (mostly) tin and antimony that form when the alloy cools. These crystals stick up out of the surface of the lead as it cools and shrinks. This is why your alloy is so shiney when you pour it, and so low in gloss when it is cool. They also reduce the gloss of your nice shiney bullet when it is deformed.)

Actually, it's hard to understand how even pure lead can be upset very much in the throat and bore of a rifle, no matter what the pressure might be. Even if the pressure is high enough to essentially make the lead into a water-like fluid, it still can't expand any further than the wall of the barrel. The most it could upset would be at the base, which might possibly be expanded to the diameter of the gas check. I've run thousands of tests and have never once seen such a thing.

One test trumps a thousand expert opinions. And I've run a LOT of tests, in everything from 30-06 gas checked bullets to plain based .357 Mag in rifles. You may get some upset of a pure or nearly pure lead bullet, especially from a short barreled rifle, but I have never seen an example from a reasonably hard alloy in a modern load for a sporter rifle.

[felix]

That's true, Molly, when the case does not obturate the hole. ... felix

[sargenv]

I wonder if you could call lead an actual solid... since at different temperatures it is actually a liquid.. same as glass, plastic, etc..

[felix]

Well, everything is like what you say, not just lead, because everything can either be a solid, liquid, or gas. That is not actually true because some items can skip one of the three PHASES, at least on earth. The concept starts with an item having three attributes: volume, temperature, mass. The scientists need some sort of standard, to allow volume and temperature vary predictability in regards to maintaining mass in one of the three states. This thought process might not be valid when discussing sub-atomic stuff, which seems nowadays there is no end to the levels possible. ... felix

[303Guy]

I wonder if you could call lead an actual solid... since at different temperatures it is actually a liquid.. same as glass, plastic, etc.. To be a solid it has to have a chrystaline structure below its melting point. Glass does not and is therefore not a true solid, i.e. it does not have a melting point, it just gets stiffer at lower temperatures but it still flows when 'solid', that's why old shop windows are not so flat and are thicker at the bases. The glass has been slowly flowing downhill.

Molly, I'm surprized you say you haven't found evidence of boolit upset after thousands of tests. I've only done a few tens of tests and I have found plenty of evidence of upset/obturation. Black powder paper patchers claim boolit upset when they patch to a bore diameter and the boolit upsets to fill the grooves. I have even found evidence of the boolit core expanding into the gap between the case mouth and throat start. Even more weired is that same boolit showed radial displacement along that upset plain as the rifling twisted the boolit. (I hope I still have that boolit. I do have pics of it which I have posted. If you like, I can post them here).

[303Guy]

Right. Here's that boolit. It's fired in a two-groove bore which has a tendancy to 'wear' into the rifling impression.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-521F.jpg

http://i388.photobucket.com/albums/oo327/303Guy/MVC-524F.jpg

http://i388.photobucket.com/albums/oo327/303Guy/MVC-525F.jpg

If anyone cannot make out from the pics what I am talking about, please ask and I'll try to take some more revealing pics.

It is quite possible that there existed a 'cold-shut' plain in the boolit (a fold in the casting in which partial freazing took place which was then covered by more molten metal, leaving a weakened plain) that coincided with the gap between case mouth and throat start. And then this with an alloy that exibits harder and softer zones - probably due to these 'cold-shut' planes.

The 'evidence' would have been preserved by the paper patch which itself compresses to hold impressions. (I realize the patch 'could' have been responsible for the 'ridge' but the mis-alignment of the rifling impression? Did only the patch slip at that plain? In the throat?)

I suspect that at the stresses within the boolit at the time of the 'upset', the metal remained plastic on the upset plain, long enough for the shear slip to occur.

[Molly]

Molly, I'm surprized you say you haven't found evidence of boolit upset after thousands of tests. I've only done a few tens of tests and I have found plenty of evidence of upset/obturation. Black powder paper patchers claim boolit upset when they patch to a bore diameter and the boolit upsets to fill the grooves. I have even found evidence of the boolit core expanding into the gap between the case mouth and throat start. Even more weired is that same boolit showed radial displacement along that upset plain as the rifling twisted the boolit. (I hope I still have that boolit. I do have pics of it which I have posted. If you like, I can post them here).

Hi 303 guy,

That's not exactly what I said. Without going back and checking what I said where (I've just finished an article on the subject for the CBA), it is my contention that I have never seen a hard cast (def: Wheelweight alloy or harder) bullet that showed significant upset of the base. To be more clear, I should limit that to smokless high power loads. Some of them were over 3000 FPS. The most I've seen is a FAINT expansion at the top of the gas check.

Now that's not to say that very soft alloys can't be found to upset, though I've never played with them. Dr. Mann's book shows plenty of upset bases - read it for qualifiers - but what he photographed were not bases expanded in the throat or bore of the gun, because they are invariably much larger than the throat or the bore. They were upset by muzzleblast. I know, he was trying to say that he had demonstrated that the pressure in the throat was high enough to upset his soft lead bullets - but they still weren't! Even if he had fired bullets made of window putty, they couldn't possibly have upset very much in the throat or bore, because they couldn't have been expanded beyond the throat / bore diameter.

Now look at the bullets you recover, and study the base, looking for evidence of upset. Does the gas check shank change diameter? Mine don't. Do you see more narrow lube grooves? I don't. Do you see dendrites reducing the shine of non-bearing surfaces? I don't. Are the non-bearing surfaces (ie, lube grooves, gas check shank) work softened noticably? Mine aren't. (Even linotype will work soften to approach pure lead hardness) In short, I see not one single piece of what logic suggests I should expect to see if a bullet upsets.

Frankly, even though it seems to happen, I don't see how even pure lead bullets can upset much: If the base upsets like Dr. Mann postulates, it would obliterate the gas check shank. Why do recovered bullets still have gas check shanks? You can argue that the shank is maintained by hydraulic presssure of the bullet lube, but that arguement is just another way of saying that they don't expand - which isn't your position as I understand it.

Base upset of soft alloys is well documented for generations, probably predating even the two piece slug guns that take two men and a booy to carry to the firing line. But that is soft alloy, selected for ability to upset. Paper patch bullets must upset very slightly, in order to take the rifling well. At least that's the current explanation for why they seem to require softer alloys for best results. And my relatively limited usage of PP agrees with this. But I used softer alloys like everyone else; My hard alloys simply don't seem to expand significantly.

You present some very nice photos of recovered PP bullets, but I don't see the evidence for base upset of hard alloys that you seem to see. Your bent bullets couldn't have been bent in the bore - at least not to that extent. And am I to understand that you cast them from hard alloys?

I suspect we're arguing apples and oranges here: I'm saying that hard cast 'normal' (gas checked bare lubricated lead) bullets don't seem to upset, and you're saying that soft, paper patched bullets do upset. But if you have a recovered gas checked hard cast lubricated bullet that shows an obliterated or noticably shortened gas check shank or lube grooves, I'd sure love to see it.

PS: You mentioned evidence of upset filling the space between the case mouth and the throat. I've seen this, especially with COW loads. It took me a while to understand it, but I think it's scraping the exterior side of the bullet as it moves from the case mouth (where it's oversized) into the bore. Something has to give in the process of the bullet sizing down to fit the bore, and I believe it's just scraping the sides of the bullet. At least, that's my explanation for why changing the bullet diameter also changes the size and thickenss of the lead ring that can result. I reported these rings in my first Fouling Shot report of COW loads, but didn't understand them at that time. Who knows, maybe I stilll don't. I'd love to be corrected.

[303Guy]

Thanks for your response Molly. I like to think we're not arguing!:mrgreen: I figured there would be a very good reason for your observations - I just didn't pick up what you meant.

There is no discernable evidence in my captured boolit of base upset. Just that curious 'twist-shear'. I can see things in that boolit that I cannot easily show in a pic because I can turn it in my fingers and control the light reflection.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-463F.jpgThe bore condition!

My alloys are of a rather 'unscientific' nature i.e. rather random! I am aiming for a reasonably soft alloy that can withstand high RPM. I am still trying to figure things out.

I think that particular boolit demonstrates the somewhat comlex nature of alloys and their behaviour. That's all. It might also be unique! Basically, that particular rifle exhibits partial shearing (or wear through of the rifling impression but this particular boolit only has that above the 'shear plane'. Below that, the rifling impression is full width and the patch did not cut through as it did above the plane. My molds are also unusual and this 'cold-shut' or chill ripling occurs quite a lot with that alloy. It's a problem I am trying to overcome. I shall attempt to take some pics to show what I mean. You may find it interesting. Its caused by the way I am trying to pour into the mold.


They were upset by muzzleblast.I find that fascinating - that the muzzle blast jet has that much energy! But believable. Only a hornet with its miniscule muzzle blast can stabilize a 60gr bullet with a 1-in-16 twist. Plus I have seen how far muzzle blast can throw an improperly secured steel suppressor!:mrgreen:

[Molly]

Thanks for your response Molly. I like to think we're not arguing!:mrgreen: I figured there would be a very good reason for your observations - I just didn't pick up what you meant. :mrgreen:

OK, 'argue' was a poor choice of words on my part. I didn't mean to imply any acrimony, simply that a disagreement existed, and that we were trying to figure out why we seemed to have different results.

Believe me, I'm not in love with my own results or theories. I've found myself wrong too many times for that, and in spite of the honesty of my convictions to the contrary. I REALLY consider the guy that shows me where I'm wrong again to be a real friend.

But until that time, I will stand by what I said: Despite the well known and established base upset of soft lead bullets in situations like muzzle loading rifles, I have yet to see any evidence of base upset in the throats of high power rifles using smokeless loads with hard cast conventional bullets.

Oh, by the way: Last night, I remembered one more piece of evidence that they don't upset: As you increase the powder charge in a given round, the width of the engraving remains constant until you approach the point where decent accuracy is lost. Then you will find the width of the engraving will increase as well, right up to the point that accuracy is completely gone. Etching will have begun at the point that the engraving begins to widen, and leading will begin to make itself evident. The etching first appears as a tiny spot on the lead surface exactly at each rifling engraving mark. This seems counterintuitive, as I would expect the fit between the bullet and the bore to be tightest there, with less potential for gas etching. However, this is the result I observed. As the powder charge is increased from this point, this spot of etching grows wider to eventually encompass the entire diameter of the bullet base, and begins to extend along the length of the bullet engraving as well.

However, you will NOT see any change in the diameter or appearance of the gas check area except for etching along the wider engraving marks at any point. I'm unsure what the correlation may be between wider engraving and loss of accuracy, but it's quite evident (to me) that base upset / distortion / obturation plays no role in it.

Unfortunately, that leaves me in the position of concluding that bullet damage in the bore seems pretty well limited to gas etching and the resultant bore leading, and that muzzle blast is the primary culpret in loss of accuracy. The correlation certainly exists, but I can't prove the connection.

I can support this conclusion mathematically, comparing the point of loss of accuracy of a 30-30 with the loss of accuracy of a 300 WinMag by using expansion ratios to compare their muzzle pressures. Muzzle pressures are such good predictors that the maximum powder charge for the 30-30 is less than half a grain of powder from the maximum predicted powder charge of the 300 Mag.

Let me rephrase that: The calculated muzzle pressure for the maximum Lyman handbook load for the 30-30 is the same as the calculated muzzle pressure for the maximum handbook load for the 300 Mag. So I know that muzzle pressure is the culprit, but I don't know what it does to the bullet. Recovered bullets still show no evidence of base upset, etc. (Unfortunately, I haven't been able to recover bullets with much more than the base from my higher powered loads.)

Speculation suggests that since the compressive strength of linotype is about 20,000 PSI, it could be that when muzzle pressure exceeds that value, the bullet is distorted or bent by the muzzle blast. However, that's just speculation: I have found no evidence of bending in the bullets I have recovered. That's why your posting of a bent bullet photo sure caught my eye.

[303Guy]

Thanks for that Molly. Boolit casting and shooting then adding paper patching is probably a whole science in itself. And that's befor we throw in all the powder characteristics thing!:holysheep

You mentioned the loss of 'shine' from alloy upset - well I get a total loss of shine with patched boolits which I put down to the patch impressions. Now I'm not so sure it's that simple.

By the way, might I ask your thoughts on boolit alloy plastic deformation over time during its passage down the bore? Fast burning powder that loses pressure quickley versus a slow powder that rises in pressure slowly and loses pressure slowly and so on? I thought a slower powder would upset a soft alloy boolit more than a fast powder of shorter peak pressure duration but others have said it doesn't work that way. (I know a certain egg and corn flour mixture while very liquid will crack and break when beaten vigorously - a dish my Mother tought me many moons ago [smilie=1: ).

[Molly]

Thanks for that Molly. Boolit casting and shooting then adding paper patching is probably a whole science in itself. And that's befor we throw in all the powder characteristics thing!:holysheep

You mentioned the loss of 'shine' from alloy upset - well I get a total loss of shine with patched boolits which I put down to the patch impressions. Now I'm not so sure it's that simple.

By the way, might I ask your thoughts on boolit alloy plastic deformation over time during its passage down the bore? Fast burning powder that loses pressure quickley versus a slow powder that rises in pressure slowly and loses pressure slowly and so on? I thought a slower powder would upset a soft alloy boolit more than a fast powder of shorter peak pressure duration but others have said it doesn't work that way. (I know a certain egg and corn flour mixture while very liquid will crack and break when beaten vigorously - a dish my Mother tought me many moons ago [smilie=1: ).

You can replicate the loss of gloss from dendrite deformation by simply squeezing a bright bullet in a vise. It will develop a sudden loss of gloss and a 'grainy' look. The graininess is the tips of dendrites pushing through the surface. This also causes the loss of gloss, for the same reason that using sandpaper on your hood will result in a loss of gloss: The resulting irregular surface tends to reflect light in all directions, rather than uniformly, like a mirror.

As I said earlier, I don't see how much deformation can occur in the bore, simply because the bore won't let the bullet deform much. As for how deformation can occur, let me sugest you go to the library and look up a good article on flow. But as a quick version, there are actually three ways a liquid can flow:
1. Dilatent flow, where there is less flow when you apply more force. This is what your mother's recipie exhibits.
2. Newtonian flow, where doubling the force applied results in doubling the rate of flow. Plain water is an excellent example.
3. Thixotropic flow, where a small increase in force or pressure results in a large increase in the fllow rate. This is often seen in paints, which will seem non-flowing until you put a little on a brush and apply it to the wall. The small shear of the brush will cause the liquid to flow out and provide a smooth paint film.

The results of any bullet deformation in the bore (or outside the bore, for that matter) will depend on the type of flow the alloy exhibits. Unfortunately, the transitory nature of the phenomenon makes determining the type of flow quite difficult. I do not know the nature, but informed speculation would sugest dilatent flow for lead alloys; The dendrites SHOULD act on an alloy much like sawdust would act on a pool of water. A bucket of water that is saturated with sawdust tends to act like a solid body that responds to a push much like one solid mass, not like a fluid at all. Granted, given time, you can scoop a handful of damp sawdust out of the bucket, but only if you do it slowly. If you try to pull it out suddenly, you're going to have a lot of water draining out of your hand for a little while.

Adding to the uncertain nature of the viscous flow of lead alloys is the effect of time; given enough time, the water and sawdust mixture will end up like water alone. The retardation of flow by the particles will slowly diminish over time, and allow the mixture to come to the same level surface that the water alone would have come to very quickly.

Don't underestimate the influence of the time factor: You can turn up the flame on a gas stove and quickly wave your hand through the flame without feeling anything but a brief warmth. Try leaving your hand in the flame for 30 seconds, and the results will be far greater, as I'm sure you can appreciate.

Similarly, if the flow of lead alloys is dilatent as I suspect, the application of the gas pressure will only serve to make the apparent hardness of the alloy (and it's resistance to deformation and upsetting) much greater. We're treading on some mighty thin speculative ice here, but I think there's a good chance that this could be why reasonably hard alloys don't seem to exhibit the newtonian flow patterns of pure lead. Pure lead should be much like water, with no dendrites (sawdust) to retard flow. But when either fluid is modified with non-liquid particles, flow changes drasticly, just as the flow of your mothers eggs changes drastically with the addittion of corn meal particles.

It is just possible that the high pressures of modern smokeless rounds actually make lead-tin-antimony alloys stronger (for a very brief time) and more resistant to flow / upsetting than measurements over long periods might suggest. In other words, it could be that such alloys resist upsetting significantly in a few thousandths of a second, but would still upset quite a bit if the pressure were applied over several seconds or minutes. Think of your mother's recipie again: If you try to stir quickly, the mix will actually harden and crack before it will stir and mix, but slower stirring will still mix OK.

Just something to turn over in your head for a while. Enjoy.

[303Guy]

Wow! Thanks for taking the time and trouble, Molly. I appreciate it and I sure did enjoy the read (I did have to concentrate, though!:mrgreen:) It's all beginning to make sense now.

Apparently, it's the corn flour that does the 'Dilatent flow' trick.

P.S. I have been looking forward in eagerness, the whole day, to your explanation, which I felt confident you would have, and you did! Thank you once again. :drinks:

[bohica2xo]

I have no trouble getting a jacketed bullet to do this.

I made some adaptors to shoot 500S&W ammo from my 505 Gibbs.

The Gibbs has a .495 x .505 bore. Everybody said it would shoot like ****. After some targets indicated that the bullets were indeed spinning just fine, we made an effort to recover a few. The all showed full bore contact, and measured .505

B.

[felix]

Excellent! ... felix

[uscra112]

Many years ago I attended a conference on ordnance technology. One paper I still recall discussed the obturation of 155mm artillery rounds. And those are STEEL. The writer had studied some hundreds of practice projectiles, which could be recovered intact since they had no explosive charge. I asked him if there would not be distortion from the terminal impact. He said no, so long as the impact was in soil, not rock.

[felix]

U-112, yep, everything expands: the projectile, case, and barrel when the round is fired. The question is by how much, when, and where the expansion occurs, and can the expansion return to their respective initial dimensions with or without user help. ... felix

[Molly]

It's all beginning to make sense now. Apparently, it's the corn flour that does the 'Dilatent flow' trick.

Yeah, you're right. Eggs alone exhibit thixotropic flow from the gellatenous whites. But filling the internal volume with so many particles of corn meal that they rub against one another changes everything, and the flow becomes dilatent.

Back when I was learning about flow, (from the dinosaurs, I think. It's been a while) I was given an example that makes it easier to visualize: Picture a river behind a log jam. While the water can still flow through the log jam, the logs slow the flow up so much that the river backs up quite a bit. Dendrites in lead are even worse, because they're more like Christmas trees than a single tree trunk. The flow retardation effect is really pronounced. And the more logs or discarded Christmas trees you have in the jam, the worse the effect on the flow will be.

That's why you can dig your fingernail into pure or nearly pure lead pretty easily: There are few or no dendrites to retard the flow of the lead away from the push of your fingernail. But alloys with a respectable level of tin and antimony dendrites can't flow to accomodate your fingernail.

Thanks for the chance to discuss cast bullet mechanisms with someone who actually conducts some tests for himself, and has a foundation for the ideas he presents. I don't know if I've convinced you of anything, but at least you have some new ideas to consider. And please don't take my ideas as proven facts just because they seem to hang together in a logical whole.

When I was young, I had some simillar 'facts' that hung together in a logical whole: Leading was because the bullet smeared off on the steel bore, and some lubricants were poor because they got rubbed completely off before the bullet was out of the bore. Tin floated to the top of a melt, and cast bullets failed at much more than 1600 FPS because they would strip the rifling when driven too fast. Perfectly reasonable and logical explanations can be given for every one of those old wives tales, and at one time or another, I believed every one of them. Listen to what I say, because I've paid a heavy price for the information I give you for free. But don't believe it without good proof. Question every bloody piece of it, and conduct your own tests to see if it's true.

[felix]

Yes, the barrel itself acts as a restrainer and is therefore a strainer to anything that moves against it. ... felix

[303Guy]

Thanks a heap Molly. It's been fun!


They all showed full bore contact, and measured .505I have speculated that such an 'obturated' bullet would be very good because the jacket would retain its 'elastic memory' while the lead core has undergone plastic deformation and so the jacket would be very tight on the core.


yep, everything expands: the projectile, case, and barrel when the round is fired.But the barrel expands mostly behind the bullet or shell. This would keep the projectile in full and firm contact with the bore all the way to the muzzle, as the pressure falls. I have wondered what role this bore expansion plays in the choice of powders and the load level. The optimum powder and charge should produce a pressure curve that matches the profile of the barrel so as to give the effect of a tapered bore. A skinny barrel would be a bit more fussy than a bull barrel I should think.

[felix]

.....The optimum powder and charge should produce a pressure curve that matches the profile of the barrel so as to give the effect of a tapered bore. A skinny barrel would be a bit more fussy than a bull barrel I should think....

You think correctly. Accuracy is determined by the swing of the barrel assuming equality between barrels. The accuracy point can be determined fairly closely by choosing the powder that maximizes the dwell time at the top of a cycle swing. "Flatter" the top, the more potential accuracy, assuming the projectile leaves the barrel during the dwell. ... felix

Some guns shoot best at full load, others just close. The warehouse experiments have shown that for most guns, the barrel should be cut at 21.75 inches, and the load adjusted to 300 fps increments to get the flattest curve. For example, one gun shoots 3300 fps, and another at 3000 for the "same" accuracy. This, of course, assumes complete powder burn in either situation, no matter the powder speed required to do so. One powder needs 45K psi to meet that criteria, and another likes 52K. Pistol powders need considerably less pressure for a positive burn, so maybe 15K would work assuming the case-bore-projectile would meet the "flat" requirement, say at 1500 fps (a 300 increment value). ... felix

An ES of ZERO would indicate without doubt a consistent powder burn. However, accuracy could be absolutely non-existant. That would be the situation when the projectile left the barrel at the wrong part of the cycle. Therefore, a compromise must be made to either one and/or both the powder speed and projectile to hone in the accuracy for a given yardage. An accurate load with a zero ES would be the one favored for undetermined target distances. For a given fixed distance, the ES does not matter in the least. But then, different accuracy will occur on a different day, guaranteed. ... felix

[jonk]

Perhaps.

Depends on the bullet.

Depends on the powder.

Depends on the bore.

There is a slight difference in my mind between upsetting into the rifling (ala late 18th century early smokless cupro-nickel clad loads made under groove size by 2-3/1000ths) and obduration (i.e. a minie ball swelling up).

I would hesitate to say that any round loaded from the breech of a gun ever obdurates other than in the most basic sense of the word, i.e. seals. Obduraiton may include sizing DOWN under this most generous definition, so long as the bullet seals to the barrel. But in the sense of swelling up, we're going to assume that most any bullet will, if not groove diameter, be of bore diameter at least. That's where I would draw the distinction.

A breech loaded bullet of at least bore diameter but not groove diameter upsets.

A muzzle loaded bullet (or breech loaded in some rare cases perhaps) of less than bore diameter obdurates.

Just my take.

[felix]

Your take is good, but dictionary check the meaning of the words obturate and obdurate. ... felix

[303Guy]

... But then, different accuracy will occur on a different day, guaranteed. ... felixAah hah! Now that I did not take in to account! Thanks for pointing it out to me.


... The warehouse experiments have shown that for most guns, the barrel should be cut at 21.75 inches, and the load adjusted to 300 fps increments to get the flattest curve. For example, one gun shoots 3300 fps, and another at 3000 for the "same" accuracy ...I remember reading about that but had forgotten about it.

Actually, what I was speculationg on (which may be nothing more than just that) is the pressure curve in the barrel producing bore expansion in such a way that the expansion is progressively less toward the muzzle so as to maintain a constant bore to bullet contact pressure. That would be over and above the harmonic effect and would likely be lost in the harmonic effect anyway. Besides, the muzzle blast effect might be more significant.

[felix]

A choked barrel is preferred for the reason stated, plus it helps guarantee constant pressure on the cutting/engraving tool making the grooves. But everything else is more important like you say because of the odds are against supreme accuracy in the first place. Fast twist helps the high pressure detriment at the muzzle, and is another reason condoms tend to always shoot better under higher pressure. A lucky gun owner is one having a gun that can shoot condoms and boolits equally without loading effort. ... felix

[303Guy]

Thanks for that, felix. Between you and Molly (and others too), I have plenty to think about for quite a while. And that's before I start thinking about boolit lubes! (One day I shall venture to make myself some 'felix lube').

Molly

Thinking about dilatent flow flow in lead alloy and how my particular alloy expands and turns inside out when fired into sand which is rather sudden, I would expect that some threshold has been reached and the energy transfer raises the temperature and exerts rather massive forces on the boolit. This would explain why such deformed boolits are so hard compared to the unfired boolit. As a kid I discovered that lead can be hardened by hammering - same mechanism.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-574F.jpg

[felix]

Keep the boolit lubes on the back burner and use various formulas to tweak the best loads, hopefully making one of them stand out as the very best one. ... felix

[Molly]

Molly

Thinking about dilatent flow flow in lead alloy and how my particular alloy expands and turns inside out when fired into sand which is rather sudden, I would expect that some threshold has been reached and the energy transfer raises the temperature and exerts rather massive forces on the boolit. This would explain why such deformed boolits are so hard compared to the unfired boolit. As a kid I discovered that lead can be hardened by hammering - same mechanism.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-574F.jpg

That's very interesting. Steel and a few other alloys will work harden rather sharply through grain refinement, but I didn't know there was any way to work harden lead or even lead alloys. How did you determine the change in hardness of the lead? What kind of lead was invloved, pure or alloyed?

I ask because - though I've never run any tests myself, all my reading suggests the opposite result; that deforming lead will soften it by breaking up the crystalline dendrite structure to sort of resemble BB's floating in the lead, with no real hardenig effect. This from a number of books on metalurgy.

I've also had commercial / professional bullet manufacturers (who are members of the CBA as well) tell me that it didn't make any difference how hard the lead was that they used to swage pistol bullets, because once it went through the swaging process, they (different alloys) were all dead soft anyhow.

So your results are especially interesting, because any time you encounter unusual results, your test is trying to tell you something.

[jonk]

Your take is good, but dictionary check the meaning of the words obturate and obdurate. ... felix

Ha! Never noticed that! Thanks Felix. So no... the bullets don't get hard, obstinate, callous, or intractable! :p

[303Guy]

That was funny!

Molly, you've forced me into thinking again!:mrgreen:
(If folks didn't do that I'd be able to spin all kinds of yarns!) :bigsmyl2:

I have not measured the 'hardness' change, just 'felt' the difference. The two occasions have been with roof sheeting (hammer) and with those boolits in the pic. By the way, those particular boolits were cast from that 'springy' sheet lead I had a thread on. The 'springyness' disappeared after melting down as was expected (and a poster suggested).

So, I can soften 'too hard an alloy' by forcing it to flow (slowly)?

I have reformed a fired boolit which included 'bumping up' and forming a hollow nose. (Notice that I don't say 'hollow point'? Or 'flat point'? - Just having fun! :mrgreen:)

[Molly]

B]Molly[/B], you've forced me into thinking again!:mrgreen: (If folks didn't do that I'd be able to spin all kinds of yarns!) :bigsmyl2:

So, I can soften 'too hard an alloy' by forcing it to flow (slowly)?

So I understand. But I'm not sure it's necessary for the flow to be slow. Seems to me that I recall someone recomending reforming the nose of a spitzer type slug to a bore riding configuration, for the express purpose of making a hunting bullet. As I recall, the logic was that radical bumping of the nose while leaving the body of the bullet unchanged would leave a hard, pressure resistant body that could be loaded hot, while the nose would be softened and would expand on impact.

Seems to me that the soft nose would just blow off on impact, and the body of the bullet would bore straight through like a Nosler. But what do I know? Anyhow, I haven't read anything more about it for quiite some time now, so mebby it didn't work out as well as it sounded.

[303Guy]

As I recall, the logic was that radical bumping of the nose while leaving the body of the bullet unchanged would leave a hard, pressure resistant body that could be loaded hot, while the nose would be softened and would expand on impactWell then, it's time for me to pull out my hollow nose forming/swaging dies and do more work on them. These 'flow' the allow quite a bit, I should emaging, as the hollow is quite large and then the cavity gets enclosed by the nose being shaped to a smaller opening and reasonable ogive.

[Molly]

Well then, it's time for me to pull out my hollow nose forming/swaging dies and do more work on them. These 'flow' the allow quite a bit, I should emaging, as the hollow is quite large and then the cavity gets enclosed by the nose being shaped to a smaller opening and reasonable ogive.

As I understand the theory, that should work quite well. I don't have any practical experience to pass on here: I always used a slip of paper between the blocks when I wanted expansion: Looked and shot like a solid bullet, but on impact, the two halves of the nose would split where the paper had separated them. The halves of the nose would then go flipping off on separate trajectories from the body of the bullet, which would bore right on through like a Nosler slug. Not only worked well, but wasn't nearly as veloity sensitive as trying to gain expansion from hollow or soft point bulets.

[Hank10]

Didn't read all of this thread so may be this was already mentioned but tests have been done with revolvers by removing the barrel and firing from just the cylinder where great expansion of the bullet bases has been observed which tells me Yes, the bullet does expand to fill whatever space is available assuming enough pressure.
H10

[Molly]

Didn't read all of this thread so may be this was already mentioned but tests have been done with revolvers by removing the barrel and firing from just the cylinder where great expansion of the bullet bases has been observed which tells me Yes, the bullet does expand to fill whatever space is available assuming enough pressure.
H10

Didn't deal with your specific example, but discussed Dr. Mann's tests with very short barrels. Briefly, the diameter of the upset bases is sufficient proof that they did NOT expand within the much smaler diameter throat. They were upset from muzzle blast, not from throat pressure. Granted, the throat pressure is adequate to upset them, but the steel barrel is also adequate to prevent upset, even if the bullet is made of putty.

Go recover a few HARD cast bullets and look at them; The gas check shank will not be shortened or larger in diameter. The lube grooves will not be shortened or larger in diameter. They do NOT upset. Check out a few boat-tail bullets too. The ultra short barrels will make them into an umberella too, but you won't find any upset bases when you dig them ot of the backstop.

[303Guy]

I always used a slip of paper between the blocks when I wanted expansion: Looked and shot like a solid bullet, but on impact, the two halves of the nose would split where the paper had separated them.Was that your idea? I wouldn't have thought of that in a million years! It's clever!:drinks:
Is there any chance of the nose halves opening up from centrifugal forces with high twist bores? (Like 1-in-10 30cals?)

[cbrick]

That idea is many decades old but I've not heard of using paper, only aluminum foil. There was an article in HandLoader several years ago about this. It's one of the things that's been on my "todolist" for a very long time.

Rick

[Molly]

Was that your idea? I wouldn't have thought of that in a million years! It's clever!:drinks:
Is there any chance of the nose halves opening up from centrifugal forces with high twist bores? (Like 1-in-10 30cals?)

Oh, heavens no! It goes back at least as far as the buffalo hunters, and may be older than that. Dunno about centrifugal opening, but I never saw any indication of it on paper targets. Probably depends on a combination of how hot your load is, how hard your alloy is, how wide the strip of paper is, and whether or not you left a tiny part of the nose tip as a solid. I always used a strip that would separate the nose from the body up to about an eighth of an inch from the tip. Worked for me, but you need to develop your loads for this: When I first played with it, I didn't leave the tip solid, and it was so destructive that I lost nearly a full shoulder off of a nice buck.

[Molly]

That idea is many decades old but I've not heard of using paper, only aluminum foil. Rick

I tried aluminum foil and it seemed tto work OK, but the thin, light foil wasn't as easy to work with as paper. Also, the paper had the added benefit of making the nose a trifle wider, so it would fit the bore a bit better. The molds we had in those doays might run as small as 0.297" in the nose. This made them really easy to feed into a o.300" bore, but they didn't get much support from the bore: Just one of the reasons that 'cast bullets were no good except with light loads', as the conventional wisdom of the day said.

[303Guy]

Getting back to 'obturation'. Molly, you have a different viewpoint and you mention several examples of what you mean. Yet I see what is to me evidence of obturation. We are seeing or interpreting things differently. You have used the example of lube grooves remaining intact. Well, having thought about it a bit, what might be confusing us is the difference between obturation, ie the boolit expanding under the force of acceleration by a small amount to fill the bore while 'crushing' the lube grooves would require a large degree of deformation. Two things could be saving the lube grooves; firstly the lube itself. Second, there could be gas bypass pressurising the lube grooves enough to partially support them (enough to prevent their total collapse). Perhaps could give that one more thought and a better expression than I can. :drinks:

[Cap'n Morgan]

303,
Check out ANeat's picture of a RN bullet, sized & lubed, and then swaged into a SWC still with the grease groove pretty much intact:

http://i64.photobucket.com/albums/h165/aneat/Swage/DSC01127.jpg

I've been thinking of doing a similar stunt to ensure more uniform bullets, by simply using the cherry the cut the mold to drill a smooth sided swaging die - perhaps with a profiled top punch, and then giving the sized and lubed bullets a good squeeze. Since the stroke length will be very short, a regular reloading press should give ample pressure.

[Molly]

>Getting back to 'obturation'. Molly, you have a different viewpoint and you mention several examples of what you mean. Yet I see what is to me evidence of obturation.

Could you be a bit more specific? What evidence of obturation do you see, and under what circumstances?

>You have used the example of lube grooves remaining intact. Well, having thought about it a bit, what might be confusing us is the difference between obturation, ie the boolit expanding under the force of acceleration by a small amount to fill the bore while 'crushing' the lube grooves would require a large degree of deformation.

It's true that the amount of foreshortening of lube grooves MAY be too small to be reliably detected and measured. However, that lack of noticable shortening is only one item in a fairly sizable package of observations, all of which suggest - some rather strongly suggesting - a lack of obturation. Consider it in light of the simultaneous lack of diameter increase at the gas check shank AND the lube grooves themselves. If obturation were occurring, it seems to me that the very firsst place it could be detected and measured is at the length of the gas check shank that is not covered by the gas check. No such expansion is observable or measurable in this area, at least in my recoveries.

>Two things could be saving the lube grooves; firstly the lube itself. Second, there could be gas bypass pressurising the lube grooves enough to partially support them (enough to prevent their total collapse). Perhaps could give that one more thought and a better expression than I can.

Good speculation, which is the basis of a good hypothesis. However, my experimental evidence is against it. As loads become increasingly more powerful, the first visible evidence of damage to the base takes the form of very faint etching, not expansion. This etching is invariably located at the edge of the gas check, and right at the land engraving mark. This is a surprise to me, as logic would suggest that this is the exact point of the tightest fit, where gas blow-by would be least likely. However, facts are facts, whether we understand them or not: This is the site of the first damage, and its nature is etching, not expansion.

As loads increase in power, the etching becomes more extensive, in both width and height. Eventually, it forms a ring around the gas shank, and extends higher on the bullet into the driving bands. Once the etching extends the entire length of the bullet, the width of the land engraving begins to increase. Careful study of this enlargement indicates that the observed increase occurs on the trailing edge of the engraving, which indicates bullet wear on the driving side of the rifling.

Note that even the slightest obturation would have the effect of compressing the bullet to remove the evidence of etching and land enlargement. The simple fact that they are formed and remain visible on the body of recovered bullets should be ample proof by itself that no obturation takes place. And they are most apparent on the base of the bullet, where obturation should be most effective at collapsing the bullet against the walls of the throat, which would wipe all evidence of the etching and enlargement away.

This may offer insights into why microgroove rifling is often considered less effective with cast bullets: The rifling engagement may be too shallow to withstand the wear, which makes it much less effective for rotating the bullet at higher power.

Be that as it may, the point is that in more powerful loads, the engraving enlargement provides an open pathway not only for propellent gases, but for any lube that may have been compressed by the process of engraving or by exposure to the propellent gas pressure: It is simply impossible for the lube to be compressed in hot loads that develop huge gaps to relieve any compression that might occur. Granted, milder loads that don't exhibit enlarged engraving might exhibit some slight pressurization, but at the same time, those loads are the least likely to produce obturation.

Here's a simple, easy and interesting experiment for you: Take an ordinary sized (but unlubricated) hard cast bullet and measure it carefully. Check diameter at the top and bottom of the gas check, across the lube grooves, and across the base driving band. Make your measurements at the mold line, so you don't inadvertently make your measurements in different places. Now cut off a bit of a barrel to give you about an inch or slightly more of clean bore. Insert the nose of the bullet, and install the assembly in a vise and compress it. Take measurements of the base and lube grooves every 1/16 inch or so of vise movement, or at least every 1/8 inch, so you can be sure of your results.

Now repeat the experiment, but don't use the vise to compress the assembly. Just snug it up just barely enough to keep it from falling out of the vise. Now whack the vise jaw solidly with a hefty hammer to produce a sudden force inpulse at least approximating the blow of the propellent. There will be sufficient 'play' in most vises to allow this to drive the bullet a short way, and require you to snug the vise up again. Keep this up until the bullet is mostly within the short barrel. Then drive the bullet out and re-measure again. See how much base upset you get, compared to just pushing it in. I'd be interested in your results.

While this isn't definitive, it's at least suggestive, and my results continue to suggest that the base doesn't upset. The much-vaunted engraving resistance and inertia of the bullet against which the pulse of the propellent gas is supposed to act simply doesn't seem to provide sufficient resistance to the blow to provide the upset so ardently defended by folks who haven't troubled to test their theories.

It's SO easy to speculate and theorize, and come up with perfectly reasonable and believable wrong answers. See my comment above about the location of gas etching for an example. If I were to just reason where the etching should occur, I sure wouldn't put it there. But reality seems to have a total disregard for my opinions and theories, doesn't it? I've gotten a few good laughs at my own ignorance over the years, and I think I've picked up a smidgon of an education in the process .

[Molly]

303,
Check out ANeat's picture of a RN bullet, sized & lubed, and then swaged into a SWC still with the grease groove pretty much intact:

Hi Capt. Morgan,

Excellent observation! And it's one I used to use myself, by reforming 0.460" (45-70) bullets to 0.445" for use in an 11 mm Mauser rifle. (Lyman used to make a special die just for this purpose!) Without lube, the grooves would collapse and present a much smaller lube groove after sizing. The bullets had to go through the 0.458 size / lube die first.

Trouble was, even the bullets with lube still came out with wider driving bands than they started with. (I didn't measure the width of the lube grooves, darn it!) But as I point out in a message a few minutes ago, this can't be compared to firing the bullet in a hot load in a rifle: Land engravings will enlarge, to provide a vent for lube, which cannot then provide hydraulic reinforcement of the bullet structure.

BTW, this also convinced me that the fellows who declare that the least sizing, the better and more accurate the bullet will be. Horse pucky! Those massively sized bullets would still cluster into 50 yard cloverleaf groups, and this from an antique iron sighted milsurp.

[largecaliberman]

I voted YES. Now it depends on the type of firearm. If you're shooting say a projectile with a BHN of 22 out of a hot load 357 magnum, I would say yes. Taking the same type of BHN and shooting it out of a mild load of 38 special, I would say the bullet would be too hard to obturate.

[Molly]

I voted YES. Now it depends on the type of firearm. If you're shooting say a projectile with a BHN of 22 out of a hot load 357 magnum, I would say yes. Taking the same type of BHN and shooting it out of a mild load of 38 special, I would say the bullet would be too hard to obturate.

Hi Largecaliberman,

Gotta disagree with you, based on one heck of a lot of recovered .357 bullets from both pistol and rifle. I fired them into pools of water, and swam down to recover the bullets. I took the guns under water and fired them so the inpact wouldn't upset the bullet nose. Never saw the slightest trace of damage that could be attributed to throat upset.

Now let me again point out that I'm talking EXCLUSIVELY about hard alloy bullets, cast from wheelweights up through linotype and even a few monotype slugs, until I realized that they were too hard to give me any detectable upset, and focused my attention on softer alloys like WW and Linotype.

Yes, SOFT lead bullets will upset: the ordinary .22 rinfire is an excellent example. But again, I'm not talking about soft lead alloys. Dr Mann illustrated some massive upset in his book, but generally didn't mention hardness of the bullets. He DID get some jacketed bullets to upset, but I'll guarantee you they didn't upset in the throat. They upset because of muzzle blast, and I'm convinced that is the cause of most if not all base upset in hard bullets.

Any military range, and a lot of civilian ranges too, will let you find plenty of fired boattailed bullets in the backstop. You will find that they will invariably retain their streamlined shape in the base, which won't show the slightest evidence of upsetting in the throat, even though Dr. Mann 'demonstrated' that jacketed bullet bases will upset. Wonder why?

WWII rifles were sometimes manufctured with more attention to volume than quality. I once owned a supposedly 7x57 rifle whose bore was the correct diameter, but the rifling had been cut so deep that it would have fit a .30 caliber bullet. While useless for normal shooting, it serves as an excellent illustration of what I am talking about. Accuracy with 7x57 ammo was negligable, but digging out some fired bullets proved very educational: You could see where the engraving on the bullet was limited to the bore, simply because the bullet was too small to fill the grooves. The 'groove' portion of the bullet was (after wiping clean) still just as bright and shiny as before it was fired. Point is, that could not have occurred if the bullet base had upset in the throat as advertised. Ergo, the base of the bullet did NOT upset in the throat, and I don't give a BLEEP what Dr. Mann said.

I got rid of the rifle for the value of it's action because I was so annoyed at the poor accuracy. Sure wish I'd kept it now: I can think of about a dozen tests I'd like to run with it now. But if you want to follow up, try shooting 7.62 bullets in a .303 Brit, or something similar. I don't care if you shoot jacketed or cast. But if you can produce a bullet that shows an expanded base, you can give me the rasberry in public. But I'm not worried. I've been down that road and hit every pothole in it. And there wasn't an expanded base in any of them.

I will also repeat an earlier challange: I would like to see the first hard lead alloy bullet whose base has expanded to eliminate, or even substantially reduce the gas check shank between the gas check and the bottom driving band. And no, I don't care if you wipe the lube out of it before you shoot it or not: The grease does not provide hydraulic resistance to upsetting as so many believe, but I'll be generous and let you shoot the bullet with no lube at all. Heck, you can even paper patch a gas check bullet for all I care. But let me see before and after pictures (or better still, the actual bullets) that show the slightest base upset, and I'll back down. I've never had anyone offer to take me up on this to date, despite all the 'experts' that say I'm wrong. They have apparently never seen any need to put their expertese to the test, but relied on Dr. Mann's erronous interpretation of his results At least Dr. Mann tested his ideas.

[303Guy]

I took the guns under water and fired them so the inpact wouldn't upset the bullet nose.I know about the Springfield Armoury tests in which they fired a 30-06 springfield under water but I didn't expect you to have done the same! Did you actually go down with the guns and fire them?


I'll be generous and let you shoot the bullet with no lube at all. Heck, you can even paper patch a gas check bullet for all I care. But let me see before and after pictures (or better still, the actual bullets) that show the slightest base upset, and I'll back down.OK, I'll take you up on that challenge.:mrgreen: Actually, I have already done it and you are right! You're also right about J-words upsetting - they don't. However, there is one instance where lead boolits do suffer base deformation (note I didn't day 'upset') and that is soft alloy boat tail cast boolits. They can be made to work but only by supporting the boat tail in a wax or lube 'cup'.

[Molly]

>I know about the Springfield Armoury tests in which they fired a 30-06 springfield under water but I didn't expect you to have done the same! Did you actually go down with the guns and fire them?

Oh yes! It was a ball! The only problem I had was that a high percentage of my bullets would simply disapear into soft mud at the bottom of the stream. But on the other hand, I had a lot of fun 'hunting' bluegills. If you give it a try, be sure you don't load the gun before it's underwater. This gives the bore a chance to fill with water. The water adds to the weight of the ejecta, but I never saw any noticable pressure rise as a result. In theory, some pressure elevation is inevitable, but I couldn't 'read' it in pressure ring or primer flattening. DO NOT tape over the muzzle and fire a factory round underwater unless you are looking for a fast way to convert your rifle into a carbine. I never did it, but understand that the bullet will upset quite nicely when it reaches the wall of water at the end of the barrel. I was never quite that curious. Oh yes, be SURE your gun is thoroughly dried when you're done. (VBG)


>OK, I'll take you up on that challenge.:mrgreen: Actually, I have already done it and you are right! You're also right about J-words upsetting - they don't.

How can that be? Dr. Mann proved that they do, even at the low pressures of a 30-40 Krag. Modern, higher pressure rounds must be even worse. (Sorry for the sarcasm. And thanks for the confirmation.)

>However, there is one instance where lead boolits do suffer base deformation (note I didn't day 'upset') and that is soft alloy boat tail cast boolits. They can be made to work but only by supporting the boat tail in a wax or lube 'cup'.

Yep! But the key word is "SOFT". I've recovered enough .22 slugs to know that soft alloys will upset very, very nicely. But my topic is HARD alloy cast bullets.

I've enjoyed discussing these matters with you, so it shouldn't have come as a surprise that you've conducted some actual testing work yourself. Keep up the good work.

[45 2.1]

I will also repeat an earlier challange: I would like to see the first hard lead alloy bullet whose base has expanded to eliminate, or even substantially reduce the gas check shank between the gas check and the bottom driving band. And no, I don't care if you wipe the lube out of it before you shoot it or not: The grease does not provide hydraulic resistance to upsetting as so many believe, but I'll be generous and let you shoot the bullet with no lube at all. Heck, you can even paper patch a gas check bullet for all I care. But let me see before and after pictures (or better still, the actual bullets) that show the slightest base upset, and I'll back down. I've never had anyone offer to take me up on this to date, despite all the 'experts' that say I'm wrong. They have apparently never seen any need to put their expertese to the test, but relied on Dr. Mann's erronous interpretation of his results At least Dr. Mann tested his ideas.

Hi Ken-
I've done the above and recovered them as you said with the GC shank expanded to band dimensions. Boolits were nominal 165 to 180 gr. cast of 50WW/50Pb with no GC before wrapping. Hundreds of them shot and recovered showing the same thing. Most loads were with SR4759 and showed the individual powder kernal impressions in the base while the GC shank was expanded to engraved band dimensions . It will require a softer alloy to do this, BUT IT DOES. No pictures though....sorry.

[Molly]

Hi Ken-
I've done the above and recovered them as you said with the GC shank expanded to band dimensions. Boolits were nominal 165 to 180 gr. cast of 50WW/50Pb with no GC before wrapping. Hundreds of them shot and recovered showing the same thing. Most loads were with SR4759 and showed the individual powder kernal impressions in the base while the GC shank was expanded to engraved band dimensions . It will require a softer alloy to do this, BUT IT DOES. No pictures though....sorry.

Sorry 45 2.1, but as you specified, it DOES require a very soft alloy, which is not the subject under discussion. We are talking about hard alloys, from wheelweights hardness and up. You are using an alloy much softer than wheelweights, so your results, though interesting, are not pertinent. There is a general agreement that SOFT alloys or pure lead WILL upset, and no arguement. But my experience is that the obturation of soft alloys is lost with harder bullets, and they apparently do not expand in the throat of the gun. This is the point of contention, or at least it is what the point of contention has evolved into.

The closest I have ever found to upset of wheelweight (or harder) alloy bullets was the rather pronounced imprint of powder granules in the base of plain based 357 WW slugs, fired with a gross overload in a Martini Carbine, and no, I won't tell you what the load was. But even there, the gross configuration of the recovered bullet bases argued for a lack of obturation: Although gas etching of the base band made it impossible to compare true diameters, the etching itself should have been eliminated or wiped off the base of the bullet if it had upset to fill the throat. To me, the mere existence of etching (much less extreme etching) argues rather convincingly that as a worst case scenario, any obturtion that MAY have occurred was exceedingly brief and limited in extent. And in conjunction with other experiences detailed previously, I don't believe any obturation occurred, even under these rather extreme conditions.

[45 2.1]

Well, you can believe whatever you want to I guess. Part of a quote from the above statement: it DOES require a very soft alloy, which is not the subject under discussion. We are talking about hard alloys, from wheelweights hardness and up. I can have a hard boolit, specifically 19 to 20 BHN, that is quite ductile and expands nicely also (50WW/50PB water dropped) which meets your WW hardness requirements and still achieve GC shank obturation in specific loads. If you want to talk about a hard alloy, from individual components, then you probably are right (for other reasons), BUT if its just hard, due to heat treatment, your idea doesn't hold a lot of water. Equating hardness with alloy components is an old idea which has little relevence with todays knowledge, however little noted it is.

This is also possible with WW and harder alloys useing rather unusual techniques. Take a very large hollow point heavy pistol boolit and fire it backwards with a heavy charge in a magnum pistol. You might find out some things.

[Cap'n Morgan]

Although gas etching of the base band made it impossible to compare true diameters, the etching itself should have been eliminated or wiped off the base of the bullet if it had upset to fill the throat.

Molly,

Are you sure the etching you mention was not a result of the muzzle blast?

[Molly]

>Well, you can believe whatever you want to I guess.

Hmmm. I believe that comment cuts in both directions.

>Part of a quote from the above statement: it DOES require a very soft alloy, which is not the subject under discussion. We are talking about hard alloys, from wheelweights hardness and up. I can have a hard boolit, specifically 19 to 20 BHN, that is quite ductile and expands nicely also (50WW/50PB water dropped) which meets your WW hardness requirements and still achieve GC shank obturation in specific loads.

Can't really comment here: I never played much with quenched alloys, because their hardness drifts with time, and I figured I had enough unknowns to deal with as it was. But I am a bit confused at the apparent discrepency in your hardness ratings. In your earlier note, you specified a 50/50 WW / lead alloy, and commented that it was quite soft. Now you rank that same composition as about 20 BHN. May I assume the difference is that some of them were quenched, and some were not? No, that can't be it: You specified that you needed a soft alloy to get obturation in your earlier note, and seem to be saying that you also get obturation when the same alloy is quenched for hardness. If that's so, your earlier comment that softness is necessary of obturation is rather confusing.

>If you want to talk about a hard alloy, from individual components, then you probably are right (for other reasons), BUT if its just hard, due to heat treatment, your idea doesn't hold a lot of water. Equating hardness with alloy components is an old idea which has little relevence with todays knowledge, however little noted it is.

I grant you that it is possible to alter the 'normal' hardness of many alloys by quenching, and that this is well known today, though not well known some years ago. I assume this is what you were referring to above. However, it is also well known today that the hardness increase so obtained is highly dependent on a number of factors, including the quench rate and alloy composition: Presence of a few percent of arsenic is critical, and more than a trace of tin results in a very rapid decay of quench hardness back to 'normal' hardnesses. The facxt of the matter is that very few bullets are cast from precisely known alloy compositions, so the results are not well predictable, especially as you move from one batch of alloy to another. The best that can be relied on is that you can obtain fairly useful hardness increases with the typical alloy, such as the 50/50 blend you are using.

This technology wasn't known when I started my quest. My early trials as a kid consisted of anything that I could get to melt. In fact, though I blush to recall the fact, my ignorance was so vast that I reasoned that the lead melted from the cores of spent jacketed bulllets had to make good cast bullets, because it was already demonstrated adequate for full power loads in jacketed bullets. My first trial produced something like 20 or 30 degrees of angle accuracy. Not minutes of angle. DEGREES. And things didn't improve a whole lot until Col Harrison published his experiments in the Rifleman. But with that to put me on a sound footing, my results in high power loads improved dramaticly, and the results of my tests began to give reproducable and readable results. I have been able to produce full power 30-06 cast loads for many years now, and have seen no need to resort to quenching. And contrary to what you seem to think, the 'normal' hardness of air cooled alloys is rather sharply defined by composition. It is also uniform and stable, properties that - in my opinion - are critical to serious testing.

>This is also possible with WW and harder alloys useing rather unusual techniques. Take a very large hollow point heavy pistol boolit and fire it backwards with a heavy charge in a magnum pistol. You might find out some things.

Oh, come on. Do you really think I have never heard of reversing a HB wadcutter? I generally got 3/4 inch mushrooms from a .38 slug. And do you really consider me so dense that it wouldn't occur to me that the same phenomenon wouldn't be effective in any caliber? Or that I couldn't predict that the expansion could be tailored by adjusting the diameter, shape and depth of the hollowpoint? Give me a little credit.

Nonetheless, I am interested in what you say. Would you be willing to send me some of your bullets, as cast, as quenched, and as recovered? I would indeed like to examine them. I can send you a PM with my address if you are interested.

[45 2.1]

Molly;851669>Well, you can believe whatever you want to I guess.

Hmmm. I believe that comment cuts in both directions.
Your correct, it does.........

>Part of a quote from the above statement: it DOES require a very soft alloy, which is not the subject under discussion. We are talking about hard alloys, from wheelweights hardness and up. I can have a hard boolit, specifically 19 to 20 BHN, that is quite ductile and expands nicely also (50WW/50PB water dropped) which meets your WW hardness requirements and still achieve GC shank obturation in specific loads.

Can't really comment here: I never played much with quenched alloys, because their hardness drifts with time with all antimonial alloys, and I figured I had enough unknowns to deal with as it was. But I am a bit confused at the apparent discrepency in your hardness ratings. You should actually learn something of this if your going to make blanket statements as you have. In your earlier note, you specified a 50/50 WW / lead alloy, and commented that it was quite soft. Now you rank that same composition as about 20 BHN. May I assume the difference is that some of them were quenched, and some were not? No, that can't be it: You specified that you needed a soft alloy to get obturation in your earlier note, and seem to be saying that you also get obturation when the same alloy is quenched for hardness. If that's so, your earlier comment that softness is necessary of obturation is rather confusing. Again, there is a lot of data out there........ read some of it and learn whats going on....................What you assume through not knowing is confusing you.

>If you want to talk about a hard alloy, from individual components, then you probably are right (for other reasons), BUT if its just hard, due to heat treatment, your idea doesn't hold a lot of water. Equating hardness with alloy components is an old idea which has little relevence with todays knowledge, however little noted it is.

I grant you that it is possible to alter the 'normal' hardness of many alloys by quenching, and that this is well known today, though not well known some years ago. For folks not taking the time to learn about it, then yes, BUT the data was there. I assume this is what you were referring to above. However, it is also well known today that the hardness increase so obtained is highly dependent on a number of factors, including the quench rate and alloy composition: Presence of a few percent of arsenic is critical, and more than a trace of tin results in a very rapid decay of quench hardness back to 'normal' hardnesses. The fact of the matter is that very few bullets are cast from precisely known alloy compositions, so the results are not well predictable, especially as you move from one batch of alloy to another. The best that can be relied on is that you can obtain fairly useful hardness increases with the typical alloy, such as the 50/50 blend you are using. You really need to learn about this instead of supposeing.....several of us have quite some years into this. What you just said is speculation when you apply it to all alloys........Lead and the alloy components you can put with it have the same virtual range of uses that steel has (nice soft steel versus very tough hard steel, remember its just steel (or lead), Ehhh)...................

This technology wasn't known when I started my quest. My early trials as a kid consisted of anything that I could get to melt. In fact, though I blush to recall the fact, my ignorance was so vast that I reasoned that the lead melted from the cores of spent jacketed bulllets had to make good cast bullets, because it was already demonstrated adequate for full power loads in jacketed bullets. My first trial produced something like 20 or 30 degrees of angle accuracy. Not minutes of angle. DEGREES. And things didn't improve a whole lot until Col Harrison published his experiments in the Rifleman. But with that to put me on a sound footing, my results in high power loads improved dramaticly, and the results of my tests began to give reproducable and readable results. I have been able to produce full power 30-06 cast loads for many years now, and have seen no need to resort to quenching. And contrary to what you seem to think, the 'normal' hardness of air cooled alloys is rather sharply defined by composition. It is also uniform and stable, properties that - in my opinion - are critical to serious testing. Refer to the first statement here. There is a lot more to alloys and there treatment out there than you know.........

>This is also possible with WW and harder alloys useing rather unusual techniques. Take a very large hollow point heavy pistol boolit and fire it backwards with a heavy charge in a magnum pistol. You might find out some things.

Oh, come on. Do you really think I have never heard of reversing a HB wadcutter? I generally got 3/4 inch mushrooms from a .38 slug. Read the original statement until you understand it, you are way off course. And do you really consider me so dense that it wouldn't occur to me that the same phenomenon wouldn't be effective in any caliber? I'm not talking about effect, i'm useing a large hollow point reversed boolit to show you that hard alloys can obturate. That depends on how strong the nose wall is versus the pressure applied to it. Think thick hard versus thinner hard and see where that leads you. Simple strength/pressure relationships occuring there. Or that I couldn't predict that the expansion could be tailored by adjusting the diameter, shape and depth of the hollowpoint? Give me a little credit. Nope....not with what you just said. Lead alloys can be as different as night and day....

Nonetheless, I am interested in what you say. Would you be willing to send me some of your bullets, as cast, as quenched, and as recovered? I would indeed like to examine them. I can send you a PM with my address if you are interested. When you've read the various sources on the web and have actually tried (instead of assuming) various alloys involving hardness, ductility, expansion, etc., then i'll discuss the situation with you. You need some better information than what you've had so far. Try here: http://www.lasc.us/CastBulletNotes.htm, various NRA publications authored by Dennis Marshall, this site and other various web sources. There is no substitute for actually trying something out yourself.

[bohica2xo]

OK kids, this thread has been entertaining, but it seems to have taken a dangerous turn.

Do NOT try shooting submerged firearms!

Yes, I am well aware of the fact that you can shoot a 9mm Glock in a pool. The glock is a rugged 9mm pistol, and even glock does not recomend this.

I spent a considerable bit of time working with NSWC Crane on the OTB (Over The Beach) issues with M16's & frogmen.

First, you do NOT want to be in the water when a firearm is discharged underwater. It is no fun at all.

I had occasion to fully submerge more than one M16 rifle before loading & firing it. It always does enough damage to the weapon to render it inoperable. With some modifications, we were able to make it "safe" - but the weapon was still a paperweight until it made it back to the armory.

Below are some photos from the modified system. When the weapon fired, 19 cartridges were blown out the bottom of the magazine. The magazine latch was blown clear out of the lower receiver. The magazine well was bulged almost .200 at the widest point.

The extractor was bent by the flowing brass, and considerable force was required to move the bolt back out of the barrel extension due to the interference of the bent extractor.

The most important thing to note is the lack of any classic "pressure signs" on the primer. If you had fired that same round of M855 on a dry range the primer would have had the same little crater.

Shooting a submerged firearm is just a bad idea all around.

http://lh4.ggpht.com/_f9mZJsRJS54/S60A07zzKmI/AAAAAAAAAHk/FfUOM4Y2B4s/s912/037_0.jpg

http://lh4.ggpht.com/_f9mZJsRJS54/S60A0QZREqI/AAAAAAAAAHU/e5xGglfMCbQ/s720/023_14.jpg

Have fun, stay safe.

B.

[runfiverun]

16"'s of water is kinda heavy compared to a 55 gr bullet.

[Molly]

> But I am a bit confused at the apparent discrepency in your hardness ratings. You should actually learn something of this if your going to make blanket statements as you have.

I'm willing. Educate me. But be aware that I have made no statement regarding the obturation (or lack thereof of any alloy or bullet except hard cast bullets. That specifically includes any statement regarding the performance of quenched bullets.

In your earlier note, you specified a 50/50 WW / lead alloy, and commented that it was quite soft. Now you rank that same composition as about 20 BHN. May I assume the difference is that some of them were quenched, and some were not? No, that can't be it: You specified that you needed a soft alloy to get obturation in your earlier note, and seem to be saying that you also get obturation when the same alloy is quenched for hardness. If that's so, your earlier comment that softness is necessary of obturation is rather confusing.

I note that you utterly failed to clarify this apparent discrepency.

>Again, there is a lot of data out there........ read some of it and learn whats going on....................What you assume through not knowing is confusing you.

If you want me to take you seriously, you need to be more specific. Exactly what have I said that your disagree with, and why? Why do you think that my knowledge (or lack thereof) of heat treating has any bearing on the results I obtained using non-heat treated bullets? It's hard for me to see the relevance.

Nonetheless, I am interested in what you say. Would you be willing to send me some of your bullets, as cast, as quenched, and as recovered? I would indeed like to examine them. I can send you a PM with my address if you are interested.

>When you've read the various sources on the web and have actually tried (instead of assuming) various alloys involving hardness, ductility, expansion, etc., then i'll discuss the situation with you. You need some better information than what you've had so far. Try here: http://www.lasc.us/CastBulletNotes.htm, various NRA publications authored by Dennis Marshall, this site and other various web sources. There is no substitute for actually trying something out yourself.[/QUOTE]

Hmmm. I don't find that a very satisfying response. I did indeed check out your reference, and it is an excellent source that I first came across some years back. However, it's been a while since I visited there, and I thank you for the reminder. I'll spend some time reviewing their offerings, and can recommend them to anyone interested. Do you have some particular offering you think I need to study?

Be aware that I have made no statement here that I have not personally tested and confirmed. I have been quite specific in describing what I did, the results I got, and the conclusions I drew from those results. Those results were repeatable, and formed a coherent pattern that varied with the alloy and pressure to provide a pretty complete picture of what really occurs in the bore. If you disagree with my intrepretation of those results, perhaps you could be a bit more specific about where you think I went wrong, and provide me with an alternative explanation that is consistent with the rest of the results.

Your participation has thus far consisted of complaints that I seem less competent than you are, but you seem unwilling to share much of your experience, describe your results, or the logic used to arrive at your conclusions. I am particularly annoyed at being called incompetent, without some description of what you consider my errors.

FYI, I corresponed with Dennis Marshall, did some alloy research with him, and have fired in competition with him. He didn't seem quite as contemptious of my knowledge of alloys as you are, and actually suggested that an alloy I designed be named after me. You can look it up in THE FOULING SHOT if you doubt my word.

I co-founded the Cast Bullet Association with Howard Thomas. You can also read of some of my own contributions in The Fouling Shot, including the "Technical Ramblings" column that I author. It seems quite popular, and to date, hasn't resulted in any complaints that i don't know what I'm talking about.

You can also read there (in the Fouling Shot) of my discovery and development of several previously unknown cast bullet technologies, including bore polishing (as opposed to fire lapping) and Cream of Wheat loads, which enables cast bullets to be shot without gas checks, lube or sizing. Phil Sharpe (a world renouned expert of earlier years) went on record as declaring that to be an absolute impossibility. But I did it. As far as I know, I'm the sole originator of the explanation of leading as a function of propellent gas etching, and explained why the old explanations of frictional rubbing and file-like abrasion from bore roughness were not valid.

But hey, I'm just an ignorant hick that knows nothing about cast bullets. I'm sure your own wisdom and achievements far outshine my own modest contributions. But perhaps you can discuss my errors and educate me, rather than just criticizing my explanations for what I've seen.

[Molly]

Quote:

OK kids, this thread has been entertaining, but it seems to have taken a dangerous turn.

Do NOT try shooting submerged firearms!

Yes, I am well aware of the fact that you can shoot a 9mm Glock in a pool. The glock is a rugged 9mm pistol, and even glock does not recomend this.

I spent a considerable bit of time working with NSWC Crane on the OTB (Over The Beach) issues with M16's & frogmen.

First, you do NOT want to be in the water when a firearm is discharged underwater. It is no fun at all.

I had occasion to fully submerge more than one M16 rifle before loading & firing it. It always does enough damage to the weapon to render it inoperable. With some modifications, we were able to make it "safe" - but the weapon was still a paperweight until it made it back to the armory.

Below are some photos from the modified system. When the weapon fired, 19 cartridges were blown out the bottom of the magazine. The magazine latch was blown clear out of the lower receiver. The magazine well was bulged almost .200 at the widest point.

The extractor was bent by the flowing brass, and considerable force was required to move the bolt back out of the barrel extension due to the interference of the bent extractor.

The most important thing to note is the lack of any classic "pressure signs" on the primer. If you had fired that same round of M855 on a dry range the primer would have had the same little crater.

Shooting a submerged firearm is just a bad idea all around.
Unquote

You make some good points, and actual experience is the most valid backing possible. Sounds like you have had plenty, and your cautions are sound.

But my own experience was under different circumstances and with different firearm mechanisms. I used bolt action rifles and a variety of revolvers. These do not present the autoloading mechanisms that were damaged in the tests you described. (Oh, and a .357 on a single shot Martini action too.) Almost all of my testing consisted of standing in the water (head out) and holding the gun underwater for firing. The exception was a single shot 22 RF, which I shot to annoy a few fish while fully underwater and using a face mask.

I was struck by two features of these tests: First, the great reduction in the intensity of the report. What would have normally been a sharp repoft (in air) was reduced to not much more than a 'thud' and a burble as the gas came up. I do not recall any shock wave that impressed me as hazardous if experienced when fully submerged. (This was many years ago, and most of my shooting (except with 22's) was with cast bullet loads that were well below full pressure. I do recall some exceptions with high prressure loads, but any unusual reports may have been forgotten. The lower pressure of most of my loads probably explains the difference between my experiences and your own.)

Secondly, I was struck by the fact that the projectiles did not even approximately follow a straight line through the water. Irregardless of caliber or pressure, they invariably described a sharply curved trajectory in the horizontal plane. Within a given load, this was consistent for each shot. I don't know, but I consider this to be a highly exaggerated expression of the trajectory drift that long range shooters experience, that is due to air turbulence based on the bullet rotation, much like a baseball curves due to air turbulence from the spinning ball. I thought it was rather neat.

[bohica2xo]

Molly, you may know a great deal about lead.

Your "underwater shooting" was a risky experiment.

The speed of the report is startling. It is the FIRST thing everyone noticed during testing.

The testing of bolt guns will reveal all sorts of failures, it really has nothing to do with the action of the M16. In fact, the gas venting through the bolt area reduces the pressure fast enough to prevent barrel bursts. I have blown up more than a few rifles - wet / dry, M40A1's to M60's. They all come apart if you screw up bad enough. I had to duplicate blowing the barrel clear out of an M2HB 50 cal once - it was not easy, but it can happen.

You "got away with it" using a revolver with (relatively) low pressure loads. The cylinder gap coupled with pressures below 20k would mitigate things rather well.

That in no way makes the idea a sound one, and I believe you should make an effort to caution against such testing outside of actual laboratory conditions.

Yes, the torque on the bullets makes them behave differently from the movie shots underwater.

B.

[Molly]

Molly, Your "underwater shooting" was a risky experiment.

The testing of bolt guns will reveal all sorts of failures, it really has nothing to do with the action of the M16.

You "got away with it" using a revolver with (relatively) low pressure loads. The cylinder gap coupled with pressures below 20k would mitigate things rather well.

That in no way makes the idea a sound one, and I believe you should make an effort to caution against such testing outside of actual laboratory conditions.

B.

Well, 'tis said that the Lord assigns special angels to watch over the affairs of fools and idiots, and that may well have been the case here too. I know for a fact that it has kept me safe from harm when by all rights I should have lost significant portions of my person.

But that being said, remember that revolvers were not my only tools: The bolt actions predominated, albiet at lower than normal pressures. It was the only way I had to recover fired bullets intact. A poor man has poor ways, as my father used to say.

I hope that the fact that I simply reported my own experience, and did not recommend the practice of shooting underwater will in some way mitigate my transgression. Should I ever discuss those experiences again, I will indeed include a strong cautionary note as you suggest.

I am quite interested in your confirmation that firing pin dents and overall priimer appearance did not reflect the theoretical and apparently very real pressure increase from the increased ejecta weight. This puzzled me at the time, and I still have no really good explanation for it. In my case, I thought it could have been that the lower pressure cast bullet loads simply had sufficient safety margin that the excursion wasn't enough to crater primers. At least that was my thought at the time, although some of the loads should have been hot enough to show some effect.

Now I have your report of a similar lack of apparent effect on primer appearance with full power factory ammo, despite obviously increased actual pressures from the increased ejecta weight. There can be no question of low pressure loads providing a margin in your tests, so my earlier thoughts were apparently groundless. (A single actual test trumps a thousand theoretical opinions!) Do you have any thoughts on the matter?

[bohica2xo]

Molly:

I could write a book about the pressure measurement mistakes in the firearms world. As is apparent in those pictures, the condition of a primer is not a clear indication of the actual pressure.

There are all sorts of things going on during ignition - it is far from being as simple as depicted in a reloading manual cartoon. I believe you have a chemistry background looking at your posts. Have you by chance read "The Chemistry of Powder & Explosives" by Tenney L Davis?

There are two big factors in the primer at the beginning. One is the Cv of the flash hole, and the second is the Brisance of the priming compound.

At the instant of ignition, there is substantial pressure within the chamber formed by the primer cup & pocket. The Cv of the flash hole control the peak pressure, and the duration. We have all seen the effect of firing only primers, or perhaps wax bullets in revolvers. The primer tends to back out of the case. The answer is to drill out the flash hole. Then the primer stays put.

Of course, we also know what happens if you load that drilled out case with a 357 mag load of 2400 behind a bullet & shoot it. The result looks like you accidentally swaped Red Dot for the 2400. It aint pretty.

The Cv of an orifice is very dependent on the differential pressure within the system. At firing, you detonate a small quantity of explosive. Primers detonate. A shock wave travels through the flash hole. If you are lighting a small quantity of fast burning powder on the other side, the pressure in the primer chamber may never even reach the peak it saw during detonation.

Now, if you are lighting a case full of 4831 in a 300 weatherby, things are different. Not only is the priming chamber exposed to the 55k peak chamber pressure, it is "held" under pressure much longer. This is why you will see primers with flow to the edges of the pocket, yet the firing pin dimple is ok, and it may not even be cratered.

This is one of the reasons that primer condition is not the best indicator of pressure. With say 5k psi in the priming chamber, it will take some time to pressureize it to 25k from the cartridge.

There is some speculation that the shockwave from detonation effectively occludes the flash hole for some period of time. If someone wants to spend 7 figures on this I am sure we can answer this question. One of my team believes very strongly that this is the reason for the primer condition in that failed case pictured. The theory is that pressures rise so fast that the case failed before the flash hole allowed enough gas to flatten the primer.

FYI, we did the underwater test on the M16 once with an 8 inch barrel stub with no gas hardware. The result was exactly as pictured. The bullet left the barrel on every weapon we blew up, regardless of barrel length.

Let's go back to the 300 weatherby for a minute. What happens if you try to hotrod it with faster powder, say IMR 4895? Primers look good @ 1 grain over max. @ 2 grains over max, the primer has a crater - but no edge flow. @ 4 grains over max, the primer is pierced, and the rifle re-cocked itself! But there is still less edge flow than the 4831 loads.

If you have been reloading for decades, you probably have noticed the changes in loading data. Copper crushers were repeatable, solid test tools. No engineer I ever met wanted to even try to translate the results into a "PSI" or worse, a "peak" pressure. They were just copper UNITS of pressure.

Piezoelectric strain gauges changed things. Now the peak pressure could be recorded, plotted & analyzed. Loading manuals became much more conservative. Go find a copy of the Speer #8 manual - and compare it to current loading specs.

I could go on all night, but the dogs expect me to get up in the morning & run with them. This old man is headed for bed.

B.

[Multigunner]

Yes, SOFT lead bullets will upset: the ordinary .22 rinfire is an excellent example. But again, I'm not talking about soft lead alloys. Dr Mann illustrated some massive upset in his book, but generally didn't mention hardness of the bullets. He DID get some jacketed bullets to upset, but I'll guarantee you they didn't upset in the throat. They upset because of muzzle blast, and I'm convinced that is the cause of most if not all base upset in hard bullets.

Any military range, and a lot of civilian ranges too, will let you find plenty of fired boattailed bullets in the backstop. You will find that they will invariably retain their streamlined shape in the base, which won't show the slightest evidence of upsetting in the throat, even though Dr. Mann 'demonstrated' that jacketed bullet bases will upset. Wonder why?

WWII rifles were sometimes manufctured with more attention to volume than quality. I once owned a supposedly 7x57 rifle whose bore was the correct diameter, but the rifling had been cut so deep that it would have fit a .30 caliber bullet. While useless for normal shooting, it serves as an excellent illustration of what I am talking about. Accuracy with 7x57 ammo was negligable, but digging out some fired bullets proved very educational: You could see where the engraving on the bullet was limited to the bore, simply because the bullet was too small to fill the grooves. The 'groove' portion of the bullet was (after wiping clean) still just as bright and shiny as before it was fired. Point is, that could not have occurred if the bullet base had upset in the throat as advertised. Ergo, the base of the bullet did NOT upset in the throat, and I don't give a BLEEP what Dr. Mann said.

I got rid of the rifle for the value of it's action because I was so annoyed at the poor accuracy. Sure wish I'd kept it now: I can think of about a dozen tests I'd like to run with it now. But if you want to follow up, try shooting 7.62 bullets in a .303 Brit, or something similar. I don't care if you shoot jacketed or cast. But if you can produce a bullet that shows an expanded base, you can give me the rasberry in public. But I'm not worried. I've been down that road and hit every pothole in it. And there wasn't an expanded base in any of them.



The .303 British Mk8 bullet (Mk8z amunition used single base nitro cellulose powders) is Boat Tailed, the original design used a step where the boat tail began to help seal and a similar boat tail bullet for long range match use with a cordite charge had a flange at that point which would expand to reduce blowby.
Boat tail bullets can upset very slightly due to pure inertia of the lead core, but the Mk8 bullet was infamous for allowing excessive blowby when fired from even a slightly eroded Enfield bore. The small opening at the base did not allow the normal amount of upset that all open flat base FMJ .303 bullets relied on for proper sealing in the more often than not oversized Enfield bores.
Inaccuracy of the Mk8 bullet when fired in Enfield rifles which show any noticable throat erosion is a long recognized situation, precisely because it doesn't upset as it should.
Cordite also eats away the bottom of the grooves faster than the lands, which increases the problem of blow by when the bore is significantly eroded by gas.

Single base powders used by the MkVIIz ammunition did not erode bores as quickly, but due to the lack of the initial thrust provided by the cordite charge of the standard MkVII ammunition the bullets of the MkVIIz often don't upset enough to prevent blowby.

I've fired salvaged bullets from old .30-30 Winchester ammo in several Enfield rifles with excellent accuracy. The .30-30 bullets being constructed for a much lower pressure range upset nicely into the throat and grooves of bores .005 or more larger than the bullets. Being a closed base with soft core and jacket the .30-30 bullets need not expand at the base itself in order to expand the body of the bullet to fill the throat and grooves. Rather than expanding by the action of high pressure gas on an exposed lead core at the base, inertia of the core results in the molecules of the lead being jammed together as the rear of the bullet is pushed forwards before the impulse is fully transmitted to the rest of the core, forcing the jacket outwards and into the grooves.
A number of the early smokeless powder rifles relied on bullet upset to fill the throat and grooves, without such upset the rifles would not have had a useable degree of accuracy.
Powders used back then were often a double base type with significant initial thrust. When the US military went with the single base pyrocellulose and MR powders they found that the previous loose allowable tolerances of bores did not allow optimum accuracy, since the single base powders did not provide sufficient initial thrust. At about the same time the Ordnance dept ordered increased thickness of jackets and alloying of the lead cores to avoid the blowing through of bullet jackets over heated by blowby gases in eroded bores.

As of the present day bores and bullets are usually closely matched in diameters, so bullets specifically designed to hold up under high velocity impacts need not rely on upset for accuracy. At the same time this makes severe throat erosion more destructive to accuracy.

So if a bullet specifically designed to function without upset shows no sign of upset thats really no suprize. If a bullet has upset to fill the throat, then traveled the length of the bore being swaged down to fit the bore diameter then how would you expect to measure any upset on the spent bullet.

As for your oversized Mauser bore, if it was that far out of spec there would not have been a good enough seal to begin with for pressure to slug out the bullet, much of the initial thrust having been lost as pure blowby.

Picking examples where the process of bullet upset can not be expected to operate properly does not preclude the fact that bullet upset is a known factor and was, and to some extent still is, relied on for best performance.

A recognized phenomena is the constriction of the bore ahead of the throat due to carbon infiltration of alligator heat cracking of the surface.
When a well worn match grade barrel is shortened at the breech, rethreaded and rechambered, this sets the constricted portion back just far enough that its still within the zone of initial thrust, the bullet now can recover from the slight constriction and undergo a secondary bumping up to once more fill out the grooves. Set back and rechambered match barrels are often more accurate than a new barrel due to a gentle taper bore effect from mechanical erosion.
The choice of many pre WW2 target shooters to use the highly erosive HiVel powders (which often burned out the throat within 400 rounds) may have been due to its high nitroglycerin content providing a much longer bumping up zone than less erosive single base powders. A eroded barrel could then be set back and rechambered several times.

[Molly]

Hi Multigunner,

I can't tell you what a delight your posting is! It is SO seldom that I get a chance to discuss firearms with someone who seems to know what they are talking about!

>The .303 British Mk8 bullet (Mk8z amunition used single base nitro cellulose powders) is Boat Tailed, the original design used a step where the boat tail began to help seal and a similar boat tail bullet for long range match use with a cordite charge had a flange at that point which would expand to reduce blowby.

My own testing and conclustions are limited to cast bullets for the most part. I have done NO testing with jacketed bullets, but being reasonably observant, I notice that I see little evidence of obturation of jacketed bullets found on the backstop. How can a boat tail - particularly a stepped design - help obturation over what might be obtained with a plain based bullet?

>Boat tail bullets can upset very slightly due to pure inertia of the lead core, but the Mk8 bullet was infamous for allowing excessive blowby when fired from even a slightly eroded Enfield bore. The small opening at the base did not allow the normal amount of upset that all open flat base FMJ .303 bullets relied on for proper sealing in the more often than not oversized Enfield bores.

>Inaccuracy of the Mk8 bullet when fired in Enfield rifles which show any noticable throat erosion is a long recognized situation, precisely because it doesn't upset as it should. Cordite also eats away the bottom of the grooves faster than the lands, which increases the problem of blow by when the bore is significantly eroded by gas.

I am not only not an expert on british munitions, I know little more than that they mostly used cordite propellent. But doesn't your report here argue against upset and obturtion, if the bullet was unable to upset enough to fill even slight bore enlargement? Also, it is my understanding that the reason for the erosive reputation of cordite was precicely because of the lack of obturation: The propellent gas was channeled through the unfilled grooves, resulting in what is generally referred to a 'gas cutting'.

>Single base powders used by the MkVIIz ammunition did not erode bores as quickly, but due to the lack of the initial thrust provided by the cordite charge of the standard MkVII ammunition the bullets of the MkVIIz often don't upset enough to prevent blowby.

Now there's an interesting observation! If single base powders failed to produce consistent obturation as you say, why then did they not produce severe erosion from gas cutting?

>I've fired salvaged bullets from old .30-30 Winchester ammo in several Enfield rifles with excellent accuracy. The .30-30 bullets being constructed for a much lower pressure range upset nicely into the throat and grooves of bores .005 or more larger than the bullets. Being a closed base with soft core and jacket the .30-30 bullets need not expand at the base itself in order to expand the body of the bullet to fill the throat and grooves. Rather than expanding by the action of high pressure gas on an exposed lead core at the base, inertia of the core results in the molecules of the lead being jammed together as the rear of the bullet is pushed forwards before the impulse is fully transmitted to the rest of the core, forcing the jacket outwards and into the grooves.

But are you not thus arguing that base obturation does not occur (at least in this example), and thus agreeing with my own conclusions? Upset of the body of the bullet is not the same as upset of the base, which is the foundation of the discussion here. (I can believe that the body of a bullet can upset under some conditions, and can cite similar reports. But I think your citation here supports my arguement against upset ofthe bullet base.)

>A number of the early smokeless powder rifles relied on bullet upset to fill the throat and grooves, without such upset the rifles would not have had a useable degree of accuracy.

Agreed, but those rifles generally used very soft lead bullets, and usually with a paper patch. My arguement has been based around the bases of hard bullets.

>Powders used back then were often a double base type with significant initial thrust. When the US military went with the single base pyrocellulose and MR powders they found that the previous loose allowable tolerances of bores did not allow optimum accuracy, since the single base powders did not provide sufficient initial thrust. At about the same time the Ordnance dept ordered increased thickness of jackets and alloying of the lead cores to avoid the blowing through of bullet jackets over heated by blowby gases in eroded bores.

Can't really coment here, except to note that a Krag with a bore below 0.311 is unusual, and I've never seen one with a 0.308 bore.

>As of the present day bores and bullets are usually closely matched in diameters, so bullets specifically designed to hold up under high velocity impacts need not rely on upset for accuracy. At the same time this makes severe throat erosion more destructive to accuracy.

Accuracy per se wasn't an important criteria for most of my testing. I'm not a match shooter. 1.5 or 2 inch groups fill my needs quite well.

>So if a bullet specifically designed to function without upset shows no sign of upset thats really no suprize.

Agreed. Although I was and am not aware that modern jacketed bullets are especially designed to prevent obturation.

>If a bullet has upset to fill the throat, then traveled the length of the bore being swaged down to fit the bore diameter then how would you expect to measure any upset on the spent bullet.

That's almost a direct quote from my earlier postings, explaining why Dr. Mann's photos of grossly expanded bullet bases could not possibly have been produced in the rifle throat. However, if a bullet is designed with grease grooves and a gas check shank, you could reasonably expect to find them at least partially obliterated by throat expansion followed by resizing into the bore. Even the lowly .22 RF base provides ample and convincing evidence of such expansion and resizing. But I see no evidene of it on recovered hard cast bullets.

>Picking examples where the process of bullet upset can not be expected to operate properly does not preclude the fact that bullet upset is a known factor and was, and to some extent still is, relied on for best performance.

Now that has me confused. Unless you speak of very minimal throat upset indeed, you seem to be saying that modern bullets are designed to prevent upset, and thus produce sub-optimal performance.

>A recognized phenomena is the constriction of the bore ahead of the throat due to carbon infiltration of alligator heat cracking of the surface.

Ummm. Minor semantic quibble if I may: The infiltration of carbon into the bore surface raises the carbon concentration, resulting in a surface that in imbrittled after it has been cooled by the rest of the barrel. This embrittlement results in micro-cracking of the bore surface when it is expanded by the subsequent shot. Continued shooting provides more carbon inflitration, which increases and deepens the cracking until microscopic flakes seperate from the brittle surface, and produces an eroded condition. The generation of a brittle surface in the process of spalling flakes isn't really a constriction per se, but the elevation of flake edges as it curls from embrittlement might produce something like a very slight but very irregular constriction.

Thanks again for your feedback. Hope you can find time to answer some of my questions. But feel free to pick and choose points to discuss in any reply you may wish to make, to keep the volume of the correspondence to a reasonable level.

[Multigunner]

But are you not thus arguing that base obturation does not occur (at least in this example), and thus agreeing with my own conclusions? Upset of the body of the bullet is not the same as upset of the base, which is the foundation of the discussion here. (I can believe that the body of a bullet can upset under some conditions, and can cite similar reports. But I think your citation here supports my arguement against upset ofthe bullet base.)
You seem to be shoveling all bullets into a pigeonhole here. The instance of a grossly undersized bullet with thin jacket and soft core upsetting in the body due to inertia is an example of upsetting being not entirely dependent on gas pressure against a soft base. It illustrates that different mechanics can produce the same result, the filling out of the throat and grooves.




>A number of the early smokeless powder rifles relied on bullet upset to fill the throat and grooves, without such upset the rifles would not have had a useable degree of accuracy.

Agreed, but those rifles generally used very soft lead bullets, and usually with a paper patch. My arguement has been based around the bases of hard bullets.

The original 8mm J bore rifles such as the GEW88 used a .318 bullet in a .321 bore, the bullet was jacketed with lead core open at the base. The purpose was to avoid excessive pressures in heavily fouled bores, the bullet bumping up to fill out the bore rather than being swaged down to fit.

As powder operating temperatures rose, the Cordite Mk1 with 58% nitroglycerine approaching 5,000 degrees use of lead bullets was feasible only with light loaded pistol cartridges which used a relatively tiny charge of flaked cordite.
When .303 cartridges were tested for possible dangers of firing with water, oil or gease in the bore it was found that when a small amount of grease was at the case mouth the velocity increased very slightly along with a noticeable rize in pressures. The conclusion was that the grease formed a momentary incompressible seal which prevented release of gas around the bullet base during the micro second it took for the bullet to bump up to fill the throat.

The .30-40 Krag originally used several types of very energetic and highly erosive powders similar to cordite, and cordite itself at one point in development.
The energetic powder coupled with a soft core and flexible jacket allowed the bullet to bump up just as the .303 did.

Tolerances of mass produced barrels and bullets were fairly loose compared to later years, and theres a limit to how much bullet upset can make up for a loose bullet to bore fit. Blowby could be all but eliminated when the barrel was new but sooner or later it would set in and erosion would increase at an accelerating rate.
A bore eroded by Cordite could remain accurate for a time so long as only cordite ammunition was used, because the cordite was energetic enough to bump up the bullets.

As pressures and velocities increased, the 1903 220 grain bullet load using a double base powder was found to overheat jackets when any noticable erosion occured greatly shortening bore life. Single base powders were then adopted for the 150 gr .30/06 higher velocity load, bullet and bore size then had to be matched near perfectly. Reduced thermal erosion allowed use of a harder jacket and upset was minimal.

As for more modern harder jacketed bullets, terminal performance at much higher velocities require that the bullet be less prone to deformation, and in the case of AP ammunition the core is a very solid steel or alloy with no elasticity at all, only a thin lead sheath between core and jacket cushioning the bullet to prevent excessive friction and allow the jacket to fill out the grooves by a swaging action. The lead sheath being trapped between jacket and core it gives in the only open path of least resistence left to it, pushing the jacket deeper into the grooves.

If you cast a bullet of alloy too hard to allow upset with the powder type and charge weight used then it will fail to upset, thats obvious.
If the bullet is designed from jump to obturate , such as the heel based Colt .38 Long then you will have efficient obturation, without which no accuracy would have been possible.
Some cartridge/firearms combinations are designed specifically to rely on upset while others are not, theres no one size fits all answer to your question.
If you use an undersized bullet cast of a too hard alloy and propel it by means of a powder charge that does not provide sufficient initial thrust to bump up the bullet then it won't seal properly and may skid in the rifling, accuracy would be poor under such conditions, and velocity inconsistent.

If bullet diameter is the same or greater than bore diameter, upset is far less of a factor, but some upset is beneficial in allowing better engraving of rifling to bullet, and when carbon infiltration of the heat check gator cracking is severe a longer energetic impulse can compensate.
Constrictions due to carbon infiltration are usually found about three to four inches further down bore from the throat. Erosion of the throat itself is much like you describe.

Ummm. Minor semantic quibble if I may: The infiltration of carbon into the bore surface raises the carbon concentration, resulting in a surface that in imbrittled after it has been cooled by the rest of the barrel. This embrittlement results in micro-cracking of the bore surface when it is expanded by the subsequent shot. Continued shooting provides more carbon inflitration, which increases and deepens the cracking until microscopic flakes seperate from the brittle surface, and produces an eroded condition. The generation of a brittle surface in the process of spalling flakes isn't really a constriction per se, but the elevation of flake edges as it curls from embrittlement might produce something like a very slight but very irregular constriction.

But further down bore the carbon is pushed under the edges raising them then bracing the raised area, metalic fouling contributes creating an aggregate that can be harder and more wear resistent than the steel itself and nearly impossible to remove even by lapping. The carbon seals the atomised metal fouling from copper solvents and the metal in turn protects the carbon from effective removal by carbon solvents. The composite surface at that point being far harder than a bronze brush or bore polishing compounds that would not wear away steel as well as the hardened fouling.

[Molly]

Hi Multigunner,

>You seem to be shoveling all bullets into a pigeonhole here. The instance of a grossly undersized bullet with thin jacket and soft core upsetting in the body due to inertia is an example of upsetting being not entirely dependent on gas pressure against a soft base. It illustrates that different mechanics can produce the same result, the filling out of the throat and grooves.

Umm, this is getting a bit hard to follow, but I don't think I am. I'm distinguishing between hard alloy bullets (which I do not believe upset ANYWHERE) and jacketed bullets with a pure or nearly pure lead core (that I don't see much evidence of upsetting with either) that (if iI understand you correctly) you feel can upset either at the base or midway along its length.

Although I don't see any evidence of jacketed upset, I can see how it might occur with a thin, soft jacket and a very soft core. I'm willing to take your word on this one, and revise my position to say that while some jacketed bullets may obturate, it is only to a slight degree at most. I base this on our common position that no bullet can expand very much in the throat due to support of the barrel limiting the expansion.

>As powder operating temperatures rose, the Cordite Mk1 with 58% nitroglycerine approaching 5,000 degrees use of lead bullets was feasible only with light loaded pistol cartridges which used a relatively tiny charge of flaked cordite.
>When .303 cartridges were tested for possible dangers of firing with water, oil or gease in the bore it was found that when a small amount of grease was at the case mouth the velocity increased very slightly along with a noticeable rize in pressures. The conclusion was that the grease formed a momentary incompressible seal which prevented release of gas around the bullet base during the micro second it took for the bullet to bump up to fill the throat.

I've heard a slightly different explanation of this: The version I heard attributed the elevated pressures to the incomprssable grease preventing or at least delaying the normal bullet release, allowing pressure to increase behind it rather sharply. This was also the explanation of the US Army for the blown up match rifles for several years at Camp Perry. The cupronickle bullet jackets would foul bores very rapidly and badly when shot 'bare'. Shooters recalled the use of grease to avoid fouling with cast bullets, and decided the same remedy would work with jacketed bullets too. They would smear MobilLube grease all over the front of the cartridge before going to the firing line. Pressures skyrocketed, and actions cracked. I think 'Hatchers Notebook' contains a pretty detailed report.

>Tolerances of mass produced barrels and bullets were fairly loose compared to later years, and theres a limit to how much bullet upset can make up for a loose bullet to bore fit. Blowby could be all but eliminated when the barrel was new but sooner or later it would set in and erosion would increase at an accelerating rate.
>A bore eroded by Cordite could remain accurate for a time so long as only cordite ammunition was used, because the cordite was energetic enough to bump up the bullets.

This makes a certain amount of sence, given what you've reported here. It's logical, and I don't know of anything to contradict it. My own conclusions about jacketed bullets not obturating were based on jacketed bullets recovered from the berm of a military range, not on a detailed research program like I used for hard cast bullets. Some of them looked like they could be reloaded and fired again. Hmmm. That triggered a recollection of a long ago article in the Rifleman, which reported that a Scandinavian marksman set up his winter range to use heavy snow drifts to backstop his bullets. Come spring, he went over the area of the drift and recovered his bullets, and actually did reload and shoot them again. I have no idea of the hardness of his bullet jackets, but any obturation had to be very slight indeed.

>As pressures and velocities increased, the 1903 220 grain bullet load using a double base powder was found to overheat jackets when any noticable erosion occured greatly shortening bore life. Single base powders were then adopted for the 150 gr .30/06 higher velocity load, bullet and bore size then had to be matched near perfectly. Reduced thermal erosion allowed use of a harder jacket and upset was minimal.

OK, this probably represents what I picked up and inspected on the base range. Many of the jackets obviously did not fill out the grooves, and exhibited no sign of friction or abrasion except on the lands.

>If you cast a bullet of alloy too hard to allow upset with the powder type and charge weight used then it will fail to upset, thats obvious.

OK, let me specify that I have not been able to find any evidence of obturation of hard alloy cast bullets with any load or pressure that provides sufficient accuracy to enable fired bullets to be found and recovered. I suppose it's possible that some upset may occur with high pressure that produces very wild shooting. Hmm. No, I've loaded to some pretty scary pressures using powders like 2400 or 4227, trying to produce base upset. I don't recall noticing any obturqtion from these loads.

>If the bullet is designed from jump to obturate , such as the heel based Colt .38 Long then you will have efficient obturation, without which no accuracy would have been possible.

Yes, and the HB 38 target loads as well, not to mention the 32 long Colt and Minne balls, and a few others as well. But again, these invariably used the softest lead possible to obtain.

>If bullet diameter is the same or greater than bore diameter, upset is far less of a factor, but some upset is beneficial in allowing better engraving of rifling to bullet, and when carbon infiltration of the heat check gator cracking is severe a longer energetic impulse can compensate.

OK, I'll take your word on this one. I have no way to test duration of my internal ballistics. But I don't see why a 0.312 bullet needs to upset to fill the bore, and produce better engraving from a 0.308 bore.

>Constrictions due to carbon infiltration are usually found about three to four inches further down bore from the throat. Erosion of the throat itself is much like you describe.
>But further down bore the carbon is pushed under the edges raising them then bracing the raised area, metalic fouling contributes creating an aggregate that can be harder and more wear resistent than the steel itself and nearly impossible to remove even by lapping. The carbon seals the atomised metal fouling from copper solvents and the metal in turn protects the carbon from effective removal by carbon solvents. The composite surface at that point being far harder than a bronze brush or bore polishing compounds that would not wear away steel as well as the hardened fouling.

I think you are describing something that may occur exclusively with jacketed bullets, which I almost never use. I have never managed to generate either throat erosion (which I have watched for) or the carbon / jacket fouling constriction you describe above in any gun I have owned, and some of them have seen quite a bit of shooting. I particularly have in mind a Garand that endured many years of regular use of hard cast bullets with sufficient power to operate the mechanism very effectively, and when I sold it, the barrel stilll looked new inside. I have also had similar results from a variety of milsurp autoloaders, though the Garand saw the greatest use by far.

Speculation might suggest that contamination of the bore by bullet lube may have been adequate to protect the bore from any erosion, but it could also be logicly argued that the presence of organic material (lube) would have increased the carbon availability and exacerbated the erosion. I lean toward the former, having seen no evidence of erosion in any of my guns.

[45 2.1]

But I am a bit confused at the apparent discrepency in your hardness ratings. You should actually learn something of this if your going to make blanket statements as you have.

I'm willing. Educate me. But be aware that I have made no statement regarding the obturation (or lack thereof of any alloy or bullet except hard cast bullets. Just what exactly do you define as a hard boolit? Two boolits can hardness test at 25 BHN..... one there strictly by alloy components, the other with very little antimony there by heat treating. Both have entirely different properties other than hardness. That specifically includes any statement regarding the performance of quenched bullets.

In your earlier note, you specified a 50/50 WW / lead alloy, and commented that it was quite soft. Now you rank that same composition as about 20 BHN. May I assume the difference is that some of them were quenched, and some were not? The proper term is heat treated.... several methods are available to do that also. No, that can't be it: You specified that you needed a soft alloy to get obturation in your earlier note, and seem to be saying that you also get obturation when the same alloy is quenched for hardness. If that's so, your earlier comment that softness is necessary of obturation is rather confusing. Your a real card........ I can see you've only dealt with high antimony alloys. Most of the information out there only deals with them also...... those alloys produce a non-ductile hard boolit. There are ways to negate that. Those have been discussed here on this board for quite some time. I see you are not aware of them.

I note that you utterly failed to clarify this apparent discrepency.

>Again, there is a lot of data out there........ read some of it and learn whats going on....................What you assume through not knowing is confusing you.

If you want me to take you seriously, you need to be more specific. Why, I have no wish for my information to be your next article. Many things talked about here have been the subject of your articles in the "Fouling Shot" as well as several places. Exactly what have I said that your disagree with, and why? Why do you think that my knowledge (or lack thereof) of heat treating has any bearing on the results I obtained using non-heat treated bullets? It's hard for me to see the relevance. It all depends whether you want a hard boolit that acts: (1) as a solid or one that (2) acts like a softpoint. Alloying with traditional elements to get a hard alloy is "old" technology now and quite limiting as to what you can achieve.

Nonetheless, I am interested in what you say. Would you be willing to send me some of your bullets, as cast, as quenched, and as recovered? I would indeed like to examine them. I can send you a PM with my address if you are interested.

>When you've read the various sources on the web and have actually tried (instead of assuming) various alloys involving hardness, ductility, expansion, etc., then i'll discuss the situation with you. You need some better information than what you've had so far. Try here: http://www.lasc.us/CastBulletNotes.htm, various NRA publications authored by Dennis Marshall, this site and other various web sources. There is no substitute for actually trying something out yourself.[/QUOTE]

Hmmm. I don't find that a very satisfying response. It was meant to allow you to do some homework and get yourself up to speed, only so far as the articles are advanced though. I did indeed check out your reference, and it is an excellent source that I first came across some years back. However, it's been a while since I visited there, and I thank you for the reminder. I'll spend some time reviewing their offerings, and can recommend them to anyone interested. Do you have some particular offering you think I need to study? Yes........ I can highly recommend you do some of your own tests with alloys other than what you know about. Ones with much reduced alloy constituents would be a good course of study. They act much differently than what you know about.

Be aware that I have made no statement here that I have not personally tested and confirmed. I have been quite specific in describing what I did, the results I got, and the conclusions I drew from those results. Those results were repeatable, and formed a coherent pattern that varied with the alloy and pressure to provide a pretty complete picture of what really occurs in the bore. If you disagree with my intrepretation of those results, perhaps you could be a bit more specific about where you think I went wrong, and provide me with an alternative explanation that is consistent with the rest of the results.

Your participation has thus far consisted of complaints that I seem less competent than you are, but you seem unwilling to share much of your experience, describe your results, or the logic used to arrive at your conclusions. I am particularly annoyed at being called incompetent, without some description of what you consider my errors. Almost all of these things are detailed in the archives here. I don't have the need to publish what i've done, though quite a few want me to write a book on the subject.

FYI, I corresponed with Dennis Marshall, did some alloy research with him, and have fired in competition with him. He didn't seem quite as contemptious of my knowledge of alloys as you are, and actually suggested that an alloy I designed be named after me. You can look it up in THE FOULING SHOT if you doubt my word.

I co-founded the Cast Bullet Association with Howard Thomas. You can also read of some of my own contributions in The Fouling Shot, including the "Technical Ramblings" column that I author. It seems quite popular, and to date, hasn't resulted in any complaints that i don't know what I'm talking about.

You can also read there (in the Fouling Shot) of my discovery and development of several previously unknown cast bullet technologies, including bore polishing (as opposed to fire lapping) and Cream of Wheat loads, which enables cast bullets to be shot without gas checks, lube or sizing. The black powder and early smokeless eras did this also, a minimum of 110 years ago. Try reading what Dr. Hudson did. Phil Sharpe (a world renouned expert of earlier years) went on record as declaring that to be an absolute impossibility. But I did it. As far as I know, I'm the sole originator of the explanation of leading as a function of propellent gas etching, and explained why the old explanations of frictional rubbing and file-like abrasion from bore roughness were not valid.
A lot of these items were in print before you were born. Not much is new, just rediscovered from time to time..... sometimes from generation to generation.

But hey, I'm just an ignorant hick that knows nothing about cast bullets. I'm sure your own wisdom and achievements far outshine my own modest contributions. But perhaps you can discuss my errors and educate me, rather than just criticizing my explanations for what I've seen. I've read your stuff in several places. I've known who you are for quite awhile also. Remember that there is no substitute for doing something yourself.... try it out.

[Molly]

45 2.1
>You should actually learn something of this if your going to make blanket statements as you have.

The only 'blanket statements' I am aware of making are factual descriptions of my observations, what I have done, the results I obtained, and the theoretical explanations I have developed for them.

> Just what exactly do you define as a hard boolit? Two boolits can hardness test at 25 BHN..... one there strictly by alloy components, the other with very little antimony there by heat treating. Both have entirely different properties other than hardness.

And I was quite specific that my reports and work applied only to what you describe as high antimony alloys, ranging from wheelweights through linotype to monotype. You may be correct that quenched low antimony alloys can have equal hardness but differ radically in other properties. But it seems unreasonable to take me to task because you don't think my results apply to an area outside what I have defined as their domain.

In your earlier note, you specified a 50/50 WW / lead alloy, and commented that it was quite soft. Now you rank that same composition as about 20 BHN.
>Your a real card........ I can see you've only dealt with high antimony alloys. Most of the information out there only deals with them also...... those alloys produce a non-ductile hard boolit. There are ways to negate that. Those have been discussed here on this board for quite some time. I see you are not aware of them.

I note that you utterly failed to clarify this apparent discrepency.

>Again, there is a lot of data out there........ read some of it and learn whats going on....................What you assume through not knowing is confusing you.

I don't see that I assume anything. You assume that my results are intended to apply in areas that are well outside their sharply defined domain. Your assumptions are your own responsibility. I will stand by what I have said.

>Why, I have no wish for my information to be your next article. Many things talked about here have been the subject of your articles in the "Fouling Shot" as well as several places.

... And now you accuse me of intending plagarism. It is true that I considered a few conversations here to be of more general interest, and passed them along to others AFTER ASKING AND RECEIVING PERMISSION TO DO SO FROM THE OTHER PARTICIPANTS. I assure you that 'your information' will have to be a great deal more specific and detailed than 'go look it up' before it will interest anyone. May I invite you to submit your skills and knowledge to peer review by sending a few articles to the Fouling Shot for their consideration? Surely someone of your skill and wisdom should receive the recognition he deserves.

>It all depends whether you want a hard boolit that acts: (1) as a solid or one that (2) acts like a softpoint. Alloying with traditional elements to get a hard alloy is "old" technology now and quite limiting as to what you can achieve.

Yes, hard alloys is now considered 'old technology' by some. But in no way does that detract from its validity or usefulness. And your 'new technology' of quenching (which is nearly as old) has yet to garner the adherents or admirers that the 'old technology' still retains. My personal explanation for this is the difficulty of obtaining consistent results without knowledge of the alloy composition ... a wisdom you seem to denegrate as you laud the quenching process it depends on.

Nonetheless, I am interested in what you say. Would you be willing to send me some of your bullets, as cast, as quenched, and as recovered? I would indeed like to examine them. I can send you a PM with my address if you are interested.

>Yes........ I can highly recommend you do some of your own tests with alloys other than what you know about. Ones with much reduced alloy constituents would be a good course of study. They act much differently than what you know about.

I find it fascinating that after decades of conducting my own tests that you would recommend I consider adopting the practice. I do not need to test softer alloys in order to validate the results I have obtained and consistently reproduced with hard alloys.

Your participation has continues to consist of complaints that I am less competent than you are, but you continue unwilling to share much of your experience, describe your results, or the logic used to arrive at your conclusions. You seem incapable of justifying your criticisms with specific valid objections to the accuracy and truthfulness of what I claim. If you have them, let's hear them. Otherwise, I grow weary of responding to hot air without the recompense of having my errors corrected. And I do not consider that complaining that my results don't apply well to something I never tested or claimed to test as a valid or specific objection.

>Almost all of these things are detailed in the archives here. I don't have the need to publish what i've done, though quite a few want me to write a book on the subject.

I would also encourage you to do so.

> The black powder and early smokeless eras did this also, a minimum of 110 years ago. Try reading what Dr. Hudson did.

My own readings of these eras recount immense effort dedicated to overcoming problems of bare lead fouling the bore with lead deposits from unpatched bullets, and with the heavy fouling of black powder. If you know of anyone who succeeded in understanding and overcoming them before me, let's hear it - and again, some specifics please!

A lot of these items were in print before you were born. Not much is new, just rediscovered from time to time..... sometimes from generation to generation.

Again, some specifics please. I recommend your criticism of blanket statements for your own consideration.

>I've read your stuff in several places. I've known who you are for quite awhile also. Remember that there is no substitute for doing something yourself.... try it out. [/QUOTE]

Mr 45 2.1, NOBODY can be a complete expert in every possible phase of cast bullet expertese. The many fields are simply too broad and complex. I take considerable care to avoid claiming skills or experience that I don't have. What I say can be taken to the bank. But don't put words in my mouth. I have REPEATEDLY limited the applicability of my reports to the hard, high antimony alloys I worked with, and find your complaints that they don't apply to ductille quenched alloys rather offensive, especially when you seem to be incapable of pointing out a single error in anything I have said.

Now you have the right of freedom of speech to say anything that isn't libelous or slanderous. But I have the right to require that my correspondence repay the effort by either teaching me something new or by allowing me the gratification of helping another. Your approach seems analgous to telling a first grader to become a brain surgeon by studying. The advice may be sound in principle, but does not seem very useful. Try being helpful. You will find it quite gratifying.

[45 2.1]

Mr 45 2.1, NOBODY can be a complete expert in every possible phase of cast bullet expertese. We were talking about hard boolits, obtainable thru several venues. Not every possible phase of cast boolit expertese. The many fields are simply too broad and complex. I take considerable care to avoid claiming skills or experience that I don't have. Thus the reason to read and study what is out there so you can learn more. What I say can be taken to the bank. But don't put words in my mouth. I have REPEATEDLY limited the applicability of my reports to the hard, high antimony alloys I worked with That revelation has been covered for many years by a lot of people and has no surprises., and find your complaints that they don't apply to ductille quenched alloys rather offensive Find it however you want, but there are several other ways to improve greatly on the old high antimonial alloys. Just why do we want a cast boolit to behave like a solid (unless you do want a solid which is brittle and shatters upon contact with solid material) when there are other ways to get there without the brittle nature your talking about., especially when you seem to be incapable of pointing out a single error in anything I have said. I could do that, but you might not like what was said. Besides, like I said, i'm not going to be the source of your next article.

Now you have the right of freedom of speech to say anything that isn't libelous or slanderous. But I have the right to require that my correspondence repay the effort by either teaching me something new or by allowing me the gratification of helping another. You indeed have the right to pass along what you've experienced, but others have done that quite well before..... I have no requirement to teach you anything, but will tell you there are other better ways of doing things. I could suggest a course of action that would show you what can be done, that is provided you would follow it to the end. Your approach seems analgous to telling a first grader to become a brain surgeon by studying. Which the first grader could do provided he went through the various grades, high school, college, medical school, residency etc. till he achieved that goal. Takes time and effort on the part of the first grader......... doesn't it. Thus the push for you to read something about alloys other than what you know. Without some base reference, anything I have to tell you wouldn't make too much sense to you since it seems to be a foriegn concept to you. The advice may be sound in principle, but does not seem very useful. Try being helpful. You will find it quite gratifying. I am, as several others could attest to, being helpfull............ you just don't perceive it that way.

[Molly]

B]I am, as several others could attest to, being helpfull............ you just don't perceive it that way.[/B]

Well sir, it seems that we have reached an area of agreement.

Goodby.

[Multigunner]

Well Molly the reasons why conclusions on the mechanism by which the lubricated match bullets caused action failures of the Springfields aren't quite the same as those in which grease caused only a slight increase in velocity and noticable rise in pressure of the .303 are because the design philosophy and stage of development, plus the maximum chamber pressures of these cartridges and their platforms are far more different than you might think. Remember that the Lee Enfields were built to far looser tolerances and the chamber pressures were far lower. The throat of the Springfield was a tighter fit and bullets were a close match to bore size. The pressure curve of the propelants was also different.

As for Mann's conclusions, I found a PDF of his work and his reasoning is very straight forwards and easily understood. Perhaps you should read it again.

Now as for a bullet of .312 in a .308 bore, its likely that bumping up would have little benefit other than to insure that the bullet did not skid in the rifling allowing gas to leak past the corners of the portion of the surface in the grooves.
The most modern long range target and snip rifle bores use grooves cut with a radius at the corners, a sharp angle there can allow gas to blowby, and any skidding in the grooves can greatly increase the problem. Some skidding is unavoidable as the bullet is first engraved at origin of rifling even if the bullet is oversized, but pressures are high enough that the material of jacket or lead body are still pressed deep enough to fill out the groove.

Instances of skidding and its effects can be illustrated by the example of a .22 bullet known to have been fired from a certain rifle not being matched to the rifle by foresic examination. In that instance excessive grease in the bore coupled with the low pressure of the cartridge allowed the copper washed bullet to skid leaving the engraving of the lands far wider than normal, a lead bullet fired in the same barrel without grease filled out the grooves and prevented skidding.
When the first Short Magazine Lee Enfields were produced they used the same MkVI cartridge as the earlier Lee Enfields, to maintain the same muzzle velocity from the 25 inch barrel of the SMLE MkI as from the LE rifle with its much longer barrel , the last fourteen inches of the bore was lapped in a reverse taper to relieve bullet friction. This appears to have worked in so far as the velocity was concerned but this also allowed blowby and the bullets which had been well engraved during the first 9 inches of travel were not able to upset enough to fill out the increased diameter further down bore, the bullets heated and skidded, the amount of skid increasing the further down bore it traveled. Accuracy was adversely affected. The reverse taper barrel was not used after the Mk1 and those Mk1 barrels were ordered replaced by 1917 with conventional barrels. No doubt the order would have gone out sooner if War had not made pulling these off the line difficult.




I have never managed to generate either throat erosion (which I have watched for) or the carbon / jacket fouling constriction you describe above in any gun I have owned, and some of them have seen quite a bit of shooting. I particularly have in mind a Garand that endured many years of regular use of hard cast bullets with sufficient power to operate the mechanism very effectively, and when I sold it, the barrel stilll looked new inside. I have also had similar results from a variety of milsurp autoloaders, though the Garand saw the greatest use by far.

Speculation might suggest that contamination of the bore by bullet lube may have been adequate to protect the bore from any erosion, but it could also be logicly argued that the presence of organic material (lube) would have increased the carbon availability and exacerbated the erosion. I lean toward the former, having seen no evidence of erosion in any of my guns.


The effects of erosion increase dramitically with increases in pressure and volume of gases.
The .276 British for which the P-13 rifle was originally designed was found to burn out its bore in a fraction of the number of rounds fired compared to the .303 when both cartridges used Cordite propellant. A cartridge loaded to a lower pressure range and lower charge weight will not erode a bore nearly as fast as the same cartridge loaded to a maximum pressure range with a heavier charge of the same or similar propellant.
Also the effects of thermal erosion are often not easily detected by the naked eye.
Theres nothing at all unusual about a fairly low intensity cast bullet load not eroding a bore to any noticable extent, thats one of the major reasons for using cast boolit loads to begin with.

Bullet lubes are there to reduce friction which would other wise lead to leading and or mechanical erosion by means of abrasion.

The effects of cabon infiltration on long range match rifles which have had many thousands of maximum power high pressure loads fired through them aren't likely to show up on bores subjected to loads of far lower intensity. The deletrious effects of choking are also not so easily noticed when the ranges fired at are a mere fraction of those in which long range match rifles compete.
On the otherhand a great many of the rifles which are used with cast boolit loads are turn of the 19th century military rifles which have had many thousands of rounds of highly erosive ammunition fired through them and the effects are obvious to the owner. Cast boolit loads are often used in such rifles in order to extend the useful shooting life of these rifles which were on their last legs so far as full power mil spec ammunition went generation ago. Some might no longer be safe to fire with modern ammunition for that matter.
The 7mm Spanish rifles for example. Some saw very little use and retain very good to excellent bores, while others of the same vintage were hard used with highly erosive double base powders. I've seen the condition of some 7mm mausers described as a "hairy" bore due to turned up edges of gator cracking stripping away fibers from cleaning patches.
Other older rifles suffered microscopic pitting all over the surface of the bore due to corrosive primers. Tests run by the American Rifleman long ago indicated that bores with such surface pitting were actually more accurate when using cast bullets than a rifle of the same type with pristine bore. the microscopic pits held globules of bullet lube which under pressure acted as microscopic ball bearing greatly reducing friction and wear of the bullet surface. The same effect can be observed in the cross hatched honing of automobile cylinders, the honed surface holding lubricating oils longer than a polished smooth surface. Bosworth on the Rifle of the 1840's also describes this effect, his tests being run using brass rifled barrels with varying degrees of surface finish.

[Molly]

Hi Multigunner,

>Well Molly the reasons why conclusions on the mechanism by which the lubricated match bullets caused action failures of the Springfields aren't quite the same as those in which grease caused only a slight increase in velocity and noticable rise in pressure of the .303 are because the design philosophy and stage of development, plus the maximum chamber pressures of these cartridges and their platforms are far more different than you might think. Remember that the Lee Enfields were built to far looser tolerances and the chamber pressures were far lower. The throat of the Springfield was a tighter fit and bullets were a close match to bore size. The pressure curve of the propelants was also different.

You make some valid points, but (If I recall correctly) Hatcher's Notebook attributed it to grease incompressability preventing normal expansion of the neck and thus normal release of the bullet. When the practice was forbidden, the cracked and broken Springfields also went away. Me? "All I know is mostly from what I read." (Will Rogers, possibly paraphrased)

>As for Mann's conclusions, I found a PDF of his work and his reasoning is very straight forwards and easily understood. Perhaps you should read it again.

Perhaps I should. Refreshment is always a good thing. But my copy (along with nearly all my books) are packed away in storage, awaiting movement to a new home. But I don't think I mis-remember his conclusion that the throat pressure is high enough to expand bullet bases, and must invariably do so. If so, his explanation doesn't account for the fact that every single bullet he fired from that progressively shortened barrel had to be upset to fill the bore. But he got good accuracy from the long barrel, and horrible accuracy and upet from the shortened testing.

Seems to me that if the throat expansion is a constant, and results change, you need to look at what else changed. In this case, muzzle blast. I have other results that suggest rather strongly that muzzle blast is a primary failure mechanism of cast bullets. It is possible to take Lyman reloading data for a given bullet and maximum powder load, and calculate a relative muzzle pressure based on the ideal gas laws. It is then possible to back calculate a maximum powder charge for the same bullet used in a completely different round that develops the same relative muzzle pressure that is within half a grain from Lyman's data for the new round. I have made such comparisons between Lyman data for the 300 Win Mag and the 30-30 Win. The comparisons are compelling, but do not provide any clues regarding the actual mechanisms of failure. I can say that failure will occur at such and such a relative muzzle pressure, but I have no clue WHY the failure occurs.

But Mann, to the best of my recollection, did not consider muzzle blast among the factors he tested.

If so, then his results and mine are different, as are our conclucions. I find that WITH HARD CAST BULLETS, no evidence of base upset is observable on recovered bullets: The gas check shanks do not exhibit the bore-filling expansion of .22 bullets, the grease grooves are not shortened or expanded, etc.

>Now as for a bullet of .312 in a .308 bore, its likely that bumping up would have little benefit other than to insure that the bullet did not skid in the rifling allowing gas to leak past the corners of the portion of the surface in the grooves.

>Instances of skidding and its effects can be illustrated by the example of a .22 bullet known to have been fired from a certain rifle not being matched to the rifle by foresic examination. In that instance excessive grease in the bore coupled with the low pressure of the cartridge allowed the copper washed bullet to skid leaving the engraving of the lands far wider than normal, a lead bullet fired in the same barrel without grease filled out the grooves and prevented skidding.

We do disagree rather sharply here. I think I have seen and reproduced what you refer to as skidding, though I refer to it as engraving enlargement. In my tests, it began to occur when etching of the gas check shank had formed a complete or nearly complete encirclement of the gas check shank. The amount and type of lube was a constant. As the power of the load increased, bullets recovered with no or minimal etching also exhibited land engraving that was equal in width to the bore lands that produced them. However, as the power of the load increased, the width of the land engraving began to increase. Gas etching naturally began to be visible in the enlarged lands, first in the base band, and then progressing forward on the body of the bullet as the load was increased. This gas blowby etching was very obviously far worse or more extensive on the side of the land that did not force rotation of the bullet: IE, gas etching didn't occur on the side of the land that was pressed tightly against the body of the bullet. I also noted that when loads were too powerful for good accuracy, leading would flash at the muzzle from the trailing edges of lands, obviously from gas blowby from enlargement of the land engraving.

Beyond the pressure levels that produced this, shooting was wild, and I was not able to recover sample bullets for examination. However, a speculation that higher loads continued to produce greater land enlargement until it merged with the neighboring land to produce a smooth bullet of substantially bore diameter seems reasonable, which would account for the complete loss of accuracy.

>When the first Short Magazine Lee Enfields were produced they used the same MkVI cartridge as the earlier Lee Enfields, to maintain the same muzzle velocity from the 25 inch barrel of the SMLE MkI as from the LE rifle with its much longer barrel , the last fourteen inches of the bore was lapped in a reverse taper to relieve bullet friction.

This is the first I've heard of such a practice! While I don't question your account, I seriously question the logic of the armorers who would deliberately reduce the
velocity and energy of a round, and produce both reduced accuracy and barrel life. It seems that the most minimal testing of the concept would have weighed heavily and prohibitivly against it.

I notice that your examples often feature historical British military rounds, and in detail that would be beyond the experience of most shooters. By any chance are you in the British Military in some capacity that woule make you privy to such detailed histories?

>The effects of erosion increase dramitically with increases in pressure and volume of gases.
>The .276 British for which the P-13 rifle was originally designed was found to burn out its bore in a fraction of the number of rounds fired compared to the .303 when both cartridges used Cordite propellant. A cartridge loaded to a lower pressure range and lower charge weight will not erode a bore nearly as fast as the same cartridge loaded to a maximum pressure range with a heavier charge of the same or similar propellant.

No arguement here! I am of course aware that typical cast bullet loads exhibit lower pressures than factory rounds, and thus have much less propensity to cause throat erosion. But the consistent gas blowby that my recovered bullets exhibited from all but the lightest loads caused me to be alert for any problems. Evidence of gas blowby that I observed began as tiny spots of erosion or etching on the base of the bullet, just in front of the gas check, and located exactly at the land engraving on the gas check. I have never understood this, as it would seem that the engraving should produce the tightest fit, and certainly far tighter than the land engraving areas. Be that as it may, the etching grew progressively more extensive until the base of the bullet was encircled, and the land engraving began to enlarge along the sides of the bullet. With so much gas blowby evident in heavy loads, it seemed prudent to be alert for evidence of bore erosion, but I never found the slightest trace.

>Also the effects of thermal erosion are often not easily detected by the naked eye.
>Theres nothing at all unusual about a fairly low intensity cast bullet load not eroding a bore to any noticable extent, thats one of the major reasons for using cast boolit loads to begin with.

Granted, it may have been possible that erosion was present but invisible to my old eyes.

>Bullet lubes are there to reduce friction which would other wise lead to leading and or mechanical erosion by means of abrasion.

I have to disagree with you there too. As a youngster, I was fed all sorts of explanations for leading. The lead was abraded off of the bullet by bore irregularities, and was soldered to the surface by the propellent gases. Or it was removed by friction, or because the lube wasn't good enough, or (ad infinitum). I reasoned that these explanations, though superficially reasonable, could not possibly all be correct. I sat out to find out exactly what mechanisms produced leading. I compressed lead against clean steel in hydraulic presses. I checked for abrasive loss by pressing bullets through barrels to check for weight loss. I simulated the passage of the bullet against the bore by chucking bullets in high speed drills. I tested with and without lubes of various types, and at low and at high temperatures. And no matter what I did, I was unable to obtain the slightest adhesion of lead to steel unless the process was sufficiently intense to produce some melting of the lead bullet. And I compared my results with that of air rifles, where lead pellets can be shot for thousands of rounds at velocities over 1000 FPS without the slightest trace of leading.

MOLTEN LEAD IS AN ABSOLUTE REQUIREMENT OF LEADING. So I turned to considering sources of heat in the rifle, which reduced to propellent gas or friction. If friction were the culpret, it should be most evident toward the muzzle, where velocity is highest. Instead, leading is generally most severe at the beginning of the bore, where propellent gas is the only significant source of heat. I started using fillers beneath the bullet to form a sort of firewall. This was successful in markedly reducing the etching and leading, though it frequently reduced accuracy. But note that these varied results were obtained with all bullets lubricated with the same type and amount of lubricant. It was a constant, and could not have been able to cause or prevent leading.

I fianlly came to the conclusion that the source of leading was the same gas erosion that produced the etching of the bullet base described above, and that the primary role of lubricants was to proovide a surface contamination of the bore that retarded adhesion of the molten microscopic droplets etched from the bullet base. I also recognize that as the temperature of the gases increase with more powerful loads, the point will be reached when the surface tension of the lead that permits soldering will be reduced enough to enable it to adhere despite any lube contamination of the surface.

Lubes do play other roles, and sometimes improtant ones: Even light loads that produce no gas etching will exhibit different accuracy potential with different lubes. I am frankly ignorant of these roles, and of how lubes perform in them.

>Other older rifles suffered microscopic pitting all over the surface of the bore due to corrosive primers. Tests run by the American Rifleman long ago indicated that bores with such surface pitting were actually more accurate when using cast bullets than a rifle of the same type with pristine bore. the microscopic pits held globules of bullet lube which under pressure acted as microscopic ball bearing greatly reducing friction and wear of the bullet surface.

This sounds reasonable, but I have seen SO many 'reasonable' explanations turn out to be worthless that I have grown quite cynical in my old age. Are you aware of any effort to verify this? I question the logic of a soft bullet being prevented from being pressed into a microscopic pit filled with lube as being superior to a hard jacketed bullet that will not be pressed into the pit in any case.

[alamogunr]

I have been following this thread closely and I must compliment both Molly and Multigunner on a discussion in which there is both agreement and disagreement. BUT! There has been none of the rancor that often follows or accompanies disagreement. Both these gentlemen are to be commended. I sincerely hope others have noticed this.

John
W.TN

[StarMetal]

Molly,

I don't tag along with your leading theory. Leading can and does occur due to high stresses of the bullet sliding against the bore because of lack of lubricant and in some instances a rough bore. Explain why, with jacketed bullets, there are jacket deposits along the whole length of the bore. I'd say the reason leading is more evident near the breech end is because that's were the bore is the most rough due to erosion inaddition to high temperatures because of the powder burning which add to the stresses of the bullet sliding along...in other words making it easier for the lead alloy to gall off onto the bore. Try shooting a non lubricated cast bullet void of any oils or dry lubes and tell us what happens. I also believe that air rifle pellets are lubed. Be nice if you could use compressed air to drive a 30 caliber non lubed bullet out of a rifle barrel at gun powder velocities and not get any leading. That would be an eye opener in the leading question. Next you'll be telling us that chalk marks the slate on the blackboard because it's melting.

[Molly]

Hi StarMetal,

> I don't tag along with your leading theory. Leading can and does occur due to high stresses of the bullet sliding against the bore because [COLOR=Blue]of lack of lubricant and in some instances a rough bore. [COLOR=Black]

So I was told as a youngster, but decades of intense interest and experiments has yet to dislodge the first evidence of it being a real failure mechanism. While rough steel will indeed abraid alloy from a cast bullet, it simply lies there: There is no trace of adhesion of the abraded lead to the steel. You can simply wipe it off with your fingertip. If you don't believe this, it's easy to test. Get a piece of mild steel and roughen it with sandpaper, sandblast or whatever strikes your fancy. Then get a hard cast bullet and start scrubbing. You'll half wear out the bulllet without seeing any adhesion. At least I did when I tried it.

>Try shooting a non lubricated cast bullet void of any oils or dry lubes and tell us what happens.

As for lack of lube, it so happens that I can indeed fire a dry, hard cast bullet in a dry bore without leading. And the bullets are also both unsized and without a gas check. The only difference between the bullet so loaded and fired and one just cast is the temperature of the bullet. I've done it many, many times, with loads up to and including Hornady handbook jacketed maximums for the round involved. Accuracy varies from fair to good. Seldom match grade, but plenty good enough for hunting. What's more, I can fire many such rounds without cleaning, and when I'm done, the bore is lead free, and as clean and bright as if it were just cleaned. How? Just add some Cream of Wheat or corn meal below the bullet. That's all. The amounts to add, and other details have been published many times.

>Explain why, with jacketed bullets, there are jacket deposits along the whole length of the bore.

I really can't explain the discrepency, and I know you are right about jacketed fouling. But I think I can give you a reasonable speculation, that the surface tension of lead is probably higher than that of copper. Surface tension is a property of all materials, and it defines the ability of one material to wet and cling to another. The lower surface tension material will invariably wet the higher surface tension material. This is why you add detergent (with very low surface tension) to water (which has a pretty high surface tension) to improve its ability to wash your dishes or clothes. I notice that most popular bullet lubes are organics (like wax or grease) with low surface tension. I suspect that one function of lubes is to contaminate the bore to make it harder for the molten lead alloy to wet it out and adhere. I speculated on this during a correspondence with Col. Harrison (the NRA cast bullet expert that devloped Alox lubes) and he said that he thought I might be right.

>I'd say the reason leading is more evident near the breech end is because that's were the bore is the most rough due to erosion in addition to high temperatures because of the powder burning which add to the stresses of the bullet sliding along...in other words making it easier for the lead alloy to gall off onto the bore.

That's logical, and it would make a good theory except for the fact that leading free loads can be assembled for the roughest pitted, rusted and eroded bore. Granted, they might be light loads, but the bore roughness and abrasiveness is still the same nonetheless. If galling of lead from the bullet surface really contributed to leading, then any rough bore should lead like mad with any load that puts the bullet out of the barrel. This is easily demonstrated to be incorrect. Try the abrasion test I described above, and I believe you will change your opinion on this matter.

>I also believe that air rifle pellets are lubed.

Yes, some of them are given a dusting of graphite or some similar dry lube, which gives them a darkened appearance. But again, many of them are obviously clean bare lead. I refer you to the Sheridan 5mm air rifle pellets, which come to mind as examples. I have a Sheridan Blue Streak that has seem sporadic but fairly extensive use over about four decades, and has yet to exhibit the first trace of adherent leading. I also own a fair number of other air rifles, and they are invariably free of leading.

>Be nice if you could use compressed air to drive a 30 caliber non lubed bullet out of a rifle barrel at gun powder velocities and not get any leading. That would be an eye opener in the leading question.

Actually, it isn't too hard to come up with an example very similar to what you describe. Air rifles are not limited to very small calibers. A very few minutes on the internet will yield high power air rifles that are used quite successfully for deer and other big game hunting. Their bullets? A home cast round ball is quite commonly used to feed such guns, but some of them are designed to use elongated lead bullets normally sold for gunpowder arms.

>Next you'll be telling us that chalk marks the slate on the blackboard because it's melting.

Nope. But you'll have to conceed that the chalk on a blackboard doesn't even begin to exhibit the adhesion that characterizes firearms leading. You can wipe it off with a cloth (or an eraser). And anyone who's ever dealt with a case of firearms leading will have no trouble telling you that the one is a far cry from the other.

You can file or abrade lead to get it into a dust-like form, and sprinkle it on a piece of clean steel. And you can also wipe it off with a rag or your finger. Like chalk, it will have no adhesion. But sprinkle a little more of that lead dust on the clean steel and set it on your stove until the lead dust melts. If you let it cool, it'll take a hammer and chisel to get the soldered mess off.

[StarMetal]

Molly,

I'm aware of the new age modern air rifles, but I'm talking about propelling say 180 grain cast 30 caliber bullet from a rifle barrel of about 24 inches to the velocity of say around 2600 fps or more unlubed. I'd like to see the bore after say 200 rounds.

I believe the surface tension of metals are in their liquid state. That wouldn't apply to what we are discussing. Maybe your were thinking of coefficient of friction such as in static and sliding.

[Multigunner]

Hi Multigunner,

>Well Molly the reasons why conclusions on the mechanism by which the lubricated match bullets caused action failures of the Springfields aren't quite the same as those in which grease caused only a slight increase in velocity and noticable rise in pressure of the .303 are because the design philosophy and stage of development, plus the maximum chamber pressures of these cartridges and their platforms are far more different than you might think. Remember that the Lee Enfields were built to far looser tolerances and the chamber pressures were far lower. The throat of the Springfield was a tighter fit and bullets were a close match to bore size. The pressure curve of the propelants was also different.

You make some valid points, but (If I recall correctly) Hatcher's Notebook attributed it to grease incompressability preventing normal expansion of the neck and thus normal release of the bullet. When the practice was forbidden, the cracked and broken Springfields also went away. Me? "All I know is mostly from what I read." (Will Rogers, possibly paraphrased)

Well you can check pages 94 0n to about 98 in Reynolds Lee Enfield and see that besides differences in cartridge and propellant the lubricants tested were also very different, and differences in result were noted when the clearance in throat or leade were greater.
The standard British "Rangoon Oil" was tested both freshly applied and after the surface dried to leave a protective coating, and Mineral Jelly was tested applied to different points of the bore and chamber.
The Mobillube fiasco that later damaged Springfields involved a very different class of grease with very different properties.




>As for Mann's conclusions, I found a PDF of his work and his reasoning is very straight forwards and easily understood. Perhaps you should read it again.

Perhaps I should. Refreshment is always a good thing. But my copy (along with nearly all my books) are packed away in storage, awaiting movement to a new home. But I don't think I mis-remember his conclusion that the throat pressure is high enough to expand bullet bases, and must invariably do so. If so, his explanation doesn't account for the fact that every single bullet he fired from that progressively shortened barrel had to be upset to fill the bore. But he got good accuracy from the long barrel, and horrible accuracy and upet from the shortened testing.
Because that shortened barrel allowed enough muzzle blast to mushroom the base of the fired bullets.
His conclusion on the upsetting in the throat was based on both extrapolation of the effect of pressures at various points in bullet travel and the concave appearance of the bullet bases of those fired from a barrel of normal length.

The experiment with shortened barrel proved sufficient pressure and acceleration forces remained to continue the upsetting action for a good way up the bore, which is why such continued acceleration can force a bullet to conform to bulged or eroded portions of the bore in the first few inches of travel, but that force drops off as the bullet reached its limit of velocity as it neared the muzzle of a full length barrel. Some pressure remained but not enough to give a sufficient G force of acceleration.




Seems to me that if the throat expansion is a constant, and results change, you need to look at what else changed. In this case, muzzle blast. I have other results that suggest rather strongly that muzzle blast is a primary failure mechanism of cast bullets. It is possible to take Lyman reloading data for a given bullet and maximum powder load, and calculate a relative muzzle pressure based on the ideal gas laws. .

Had to shorten the post a bit

If the bullet base is deformed by muzzle blast inaccuracy is the result, just as it would be if the bullet base were deformed by any other means before loading.
Gas checks reduce such damage and allow stronger charges. Card over charge wads also acted to reduce damage to bullet bases and reduce blowby.
Without its over the charge wad the MkVII .303 burned out barrels in less than 2,000 rounds, with the card average bore life was 12,000 rounds.
Card wads were common with heavily charged BP cartridges and Express cartridges.




But Mann, to the best of my recollection, did not consider muzzle blast among the factors he tested.
You should look over those photos again. Also remember that actual target rifles of his day had very long barrels and minimal muzzle blast, and residual pressures after exit of the bullet were a great deal lower than with smokeless powders of similar energy. BP muzzle blasts are impressive, but thats due to the mass of ejecta not pressure or heat, which is a fraction of that of even mild smokeless powders.




If so, then his results and mine are different, as are our conclucions. I find that WITH HARD CAST BULLETS, no evidence of base upset is observable on recovered bullets: The gas check shanks do not exhibit the bore-filling expansion of .22 bullets, the grease grooves are not shortened or expanded, etc.
From what you've said you use very light loads and your group sizes indicate that you might get better accuracy with either a slight increase in the load or a slightly softer bullet. BP target rifles in a similar velocity class printed far tighter groups than you find acceptable. One holer ten shot groups at 200 yards were not uncommon for the .32-40 target rifles of Harry Pope for one example and this without a gas check and only a thin over charge card wad. Those rifles generally used a false muzzle and a sealed blank charge rather than loading as a normal breech loader of course.



>Now as for a bullet of .312 in a .308 bore, its likely that bumping up would have little benefit other than to insure that the bullet did not skid in the rifling allowing gas to leak past the corners of the portion of the surface in the grooves.

>Instances of skidding and its effects can be illustrated by the example of a .22 bullet known to have been fired from a certain rifle not being matched to the rifle by foresic examination. In that instance excessive grease in the bore coupled with the low pressure of the cartridge allowed the copper washed bullet to skid leaving the engraving of the lands far wider than normal, a lead bullet fired in the same barrel without grease filled out the grooves and prevented skidding.

We do disagree rather sharply here. I think I have seen and reproduced what you refer to as skidding, though I refer to it as engraving enlargement. In my tests, it began to occur when etching of the gas check shank had formed a complete or nearly complete encirclement of the gas check shank. The amount and type of lube was a constant. As the power of the load increased, bullets recovered with no or minimal etching also exhibited land engraving that was equal in width to the bore lands that produced them. However, as the power of the load increased, the width of the land engraving began to increase. Gas etching naturally began to be visible in the enlarged lands, first in the base band, and then progressing forward on the body of the bullet as the load was increased. This gas blowby etching was very obviously far worse or more extensive on the side of the land that did not force rotation of the bullet: IE, gas etching didn't occur on the side of the land that was pressed tightly against the body of the bullet. I also noted that when loads were too powerful for good accuracy, leading would flash at the muzzle from the trailing edges of lands, obviously from gas blowby from enlargement of the land engraving.

Beyond the pressure levels that produced this, shooting was wild, and I was not able to recover sample bullets for examination. However, a speculation that higher loads continued to produce greater land enlargement until it merged with the neighboring land to produce a smooth bullet of substantially bore diameter seems reasonable, which would account for the complete loss of accuracy.
Sounds like you had a very oversized throat or undersized bullet to begin with to allow that much blowby, a too hard alloy would contribute.
The skidding of that .22 bullet due to grease in the bore was a finding of forensic science, and cited in the literature. One causation does not not cancel out another causation.
Your instance of blowby damage confirms my previous examples of blowby damage when bullets do not bump up to seal properly. Without a proper bullet to bore seal things begin to go wrong quickly.




>When the first Short Magazine Lee Enfields were produced they used the same MkVI cartridge as the earlier Lee Enfields, to maintain the same muzzle velocity from the 25 inch barrel of the SMLE MkI as from the LE rifle with its much longer barrel , the last fourteen inches of the bore was lapped in a reverse taper to relieve bullet friction.

This is the first I've heard of such a practice! While I don't question your account, I seriously question the logic of the armorers who would deliberately reduce the
velocity and energy of a round, and produce both reduced accuracy and barrel life. It seems that the most minimal testing of the concept would have weighed heavily and prohibitivly against it.
You aren't the only one to think this a remarkably ill advised practice, and it didn't take long for it to be revealed as very counter productive.
British military thinking of the day put far too much emphasis on massed volley fire at extreme ranges, to the detrement of precision closer range individual marksmanship.
Remaining shootable examples of the SMLE MkI are rare, and many were rebarreled after 1917 so not many still have the reverse taper bore. One thing to look for if you ever run across one is that in extreme examples the bore can measure closer to 8mm, and sometimes these rifles were condemned as worn out because they couldn't pass the later standard .303 muzzle erosion plug gauge test even when in unfired condition.




I notice that your examples often feature historical British military rounds, and in detail that would be beyond the experience of most shooters. By any chance are you in the British Military in some capacity that woule make you privy to such detailed histories?

Most all the sources I cite can be downloaded free from the net. I've long had an interest in late 19th century fire arms designs, the Lee Enfields are just one of many, and much more detailed information can be found on their development than can be found on most any military rifle in their class.
Since the .303 cartridge was one of the first smaller bore high velocity rounds and began as a black powder load using compressed cylinders of powder, its development is especially instructive.




>The effects of erosion increase dramitically with increases in pressure and volume of gases.
>The .276 British for which the P-13 rifle was originally designed was found to burn out its bore in a fraction of the number of rounds fired compared to the .303 when both cartridges used Cordite propellant. A cartridge loaded to a lower pressure range and lower charge weight will not erode a bore nearly as fast as the same cartridge loaded to a maximum pressure range with a heavier charge of the same or similar propellant.

No arguement here! I am of course aware that typical cast bullet loads exhibit lower pressures than factory rounds, and thus have much less propensity to cause throat erosion. But the consistent gas blowby that my recovered bullets exhibited from all but the lightest loads caused me to be alert for any problems. Evidence of gas blowby that I observed began as tiny spots of erosion or etching on the base of the bullet, just in front of the gas check, and located exactly at the land engraving on the gas check. I have never understood this, as it would seem that the engraving should produce the tightest fit, and certainly far tighter than the land engraving areas. Be that as it may, the etching grew progressively more extensive until the base of the bullet was encircled, and the land engraving began to enlarge along the sides of the bullet. With so much gas blowby evident in heavy loads, it seemed prudent to be alert for evidence of bore erosion, but I never found the slightest trace.
You might try a slightly softer bullet or an over the charge card wad if you intend to use such light loads exclusively.
If your bullets are too hard stepping up the powder charge may not be enough to bump up the bullets enough to form a gas tight seal.




>Also the effects of thermal erosion are often not easily detected by the naked eye.
>Theres nothing at all unusual about a fairly low intensity cast bullet load not eroding a bore to any noticable extent, thats one of the major reasons for using cast boolit loads to begin with.

Granted, it may have been possible that erosion was present but invisible to my old eyes.

Usually early erosion is very uniform, and more often than not will erode the bottom of the grooves faster than the top of the lands, giving the appearance of a bore with little wear.
Mechanical abrasion wears away the top of the land faster than the bottom of the grooves.



>Bullet lubes are there to reduce friction which would other wise lead to leading and or mechanical erosion by means of abrasion.

I have to disagree with you there too. As a youngster, I was fed all sorts of explanations for leading. The lead was abraded off of the bullet by bore irregularities, and was soldered to the surface by the propellent gases. Or it was removed by friction, or because the lube wasn't good enough, or (ad infinitum). I reasoned that these explanations, though superficially reasonable, could not possibly all be correct. I sat out to find out exactly what mechanisms produced leading. I compressed lead against clean steel in hydraulic presses. I checked for abrasive loss by pressing bullets through barrels to check for weight loss. I simulated the passage of the bullet against the bore by chucking bullets in high speed drills. I tested with and without lubes of various types, and at low and at high temperatures. And no matter what I did, I was unable to obtain the slightest adhesion of lead to steel unless the process was sufficiently intense to produce some melting of the lead bullet. And I compared my results with that of air rifles, where lead pellets can be shot for thousands of rounds at velocities over 1000 FPS without the slightest trace of leading.

MOLTEN LEAD IS AN ABSOLUTE REQUIREMENT OF LEADING. So I turned to considering sources of heat in the rifle, which reduced to propellent gas or friction. If friction were the culpret, it should be most evident toward the muzzle, where velocity is highest. Instead, leading is generally most severe at the beginning of the bore, where propellent gas is the only significant source of heat. I started using fillers beneath the bullet to form a sort of firewall. This was successful in markedly reducing the etching and leading, though it frequently reduced accuracy. But note that these varied results were obtained with all bullets lubricated with the same type and amount of lubricant. It was a constant, and could not have been able to cause or prevent leading.

I fianlly came to the conclusion that the source of leading was the same gas erosion that produced the etching of the bullet base described above, and that the primary role of lubricants was to proovide a surface contamination of the bore that retarded adhesion of the molten microscopic droplets etched from the bullet base. I also recognize that as the temperature of the gases increase with more powerful loads, the point will be reached when the surface tension of the lead that permits soldering will be reduced enough to enable it to adhere despite any lube contamination of the surface.

Lubes do play other roles, and sometimes improtant ones: Even light loads that produce no gas etching will exhibit different accuracy potential with different lubes. I am frankly ignorant of these roles, and of how lubes perform in them.

I've cleaned a lot of lead out of old rifles, the softer the pellet the more leading, many air rifle pellets these days use very fine coatings to reduce leading, my favorite is the Beeman with antifriction coating.
The high pressure clean air or CO2 of pre charged guns blows out much fouling , but the compression generated heat of powerful spring piston guns can bake on oils to clog rifling with a laquer deposit.
In any case the bearing surface of most pellets is a tiny fraction of one percent that of even a .22 rimfire bullet.

I've fired .36 round balls without lube , when I first began BP shooting in the late sixties. When no lube was used the corners of the grooves showed streamers of lead after the first shot had burned away any preservative grease left in the bore. With even a minimum of lube over the bullets no leading occured at all.




>Other older rifles suffered microscopic pitting all over the surface of the bore due to corrosive primers. Tests run by the American Rifleman long ago indicated that bores with such surface pitting were actually more accurate when using cast bullets than a rifle of the same type with pristine bore. the microscopic pits held globules of bullet lube which under pressure acted as microscopic ball bearing greatly reducing friction and wear of the bullet surface.

This sounds reasonable, but I have seen SO many 'reasonable' explanations turn out to be worthless that I have grown quite cynical in my old age. Are you aware of any effort to verify this? I question the logic of a soft bullet being prevented from being pressed into a microscopic pit filled with lube as being superior to a hard jacketed bullet that will not be pressed into the pit in any case.

Not just reasonable, its been proven by exhaustive scientific testing. I once had a reprint of Bosworth on the Rifle which goes into great detail in testing of each of his claims, Bosworth was a noted Marine Engineer and avid shooter, and one of if not the first to mount a telescopic sight on a fire arm, though only as a test rig to prove the potential accuracy of rifled short pistol barrels. He used a surveyors transit on a removalable mounting for these tests. His investigations into metalurgy of the day are especially note worthy.

The testing recounted in the American Rifleman involved careful measurements of velocity as well as accuracy with barrels at various stages of "seasoning".

I've also noted that old military rifles who's bores show the grayish texture of age are less prone to copper fouling than a highly polished bore.
Makers of modern target rifle barrels have begun to use a similar surface texturing in their barrels to reduce jacket fouling.

If the pitting s even a tiny bit larger than the near microscopic size then the situation is reversed, with metal fouling increasing greatly.
A seasoned bore may only show a slightly graying of the metal, like an old pocket knife blade. Thats about the optimum for this effect. Any darker and the effect is reversed.

You can asked traditional Muzzle Loader shooters, they have begun to rediscover the benefits of a properly seasoned bore over a new polished bore.

[Molly]

Hi StarMetal

>I'm aware of the new age modern air rifles, but I'm talking about propelling say 180 grain cast 30 caliber bullet from a rifle barrel of about 24 inches to the velocity of say around 2600 fps or more unlubed. I'd like to see the bore after say 200 rounds.

As I said, this is quite doable with granulated cereal fillers. The fillers compact behind the bullet and positively prevent passage of propellent gas which would otherwise etch the bullet and lead the barrel. No etching means no leading, and you can run as many hundreds of bullets through it as you want, but you'll still have a bright clean unleaded bore.

Out of curiosity, why do you seem to consider the air rifle example invalid when considering leading? They can develop velocities WELL over 1000 fps, which should be more than adequate to settle the leading question. Compare their velocities with the leading one can generate from a pistol at LESS than 1000 fps: If leading can occur at low velocity, it should occur from higher velocity if all the pertinent factors are present. The fact that air rifles do not generate leading seems ample evidence that they do not encompass the critical factor. Considering the many tests that indicate that leading adhesion occurs only when the alloy has been melted, attributing leading to gas etching seems a given.

>I believe the surface tension of metals are in their liquid state. That wouldn't apply to what we are discussing. Maybe your were thinking of coefficient of friction such as in static and sliding.

No, I didn't mis-speak. All physical materials (inclucing gases) have a surface tension value, although the surface tension of liquids is admittedly the most frequently studied and used. Lead or copper alloys are no exceptions, whether they are solid or molten. The surface tension shifts with temperature, and you can actually observe this by laying a metal panel with a speck of lube on a hotplate and turing the heat on. The solid lube will be seen to have little tendency to wet the panel and spread out into a thin film at first. But as the system heats, it will melt (lowering its surface tension) and spread.

One can also easily see differences in surface tension of solid materials. Simply place several different materials (wood, copper, steel, linotype, etc) together, and have a sample of a liquid such as olive oil handy. Gently place a droplet of oil on each and observe the differences. The oil will spread rapidly on some surfaces, and slowly on others. You are probably already familiar with this in the form of a teflon frying pan: The reason nothing sticks to it is because the surface tension is so low that nothing can wet it out. You may put a droplet of oil on it, but it will just form a bead, and won't spread out at all.

In a more pertinent example, tin is used in lead alloys because it has a very low surface tension. A little bit will lower the surface tension of the alloy and allow it to flow and make good castings. However, too much tin will lower the surface tension so much that you will have solder, and lots of trouble from leading.

[Multigunner]

Gas blowby can greatly increase leading, but its not the only source of heat in the passage of a bullet up the bore.

Gas thermal transfer to the surface of the bore heats only the surface, while friction from bullet passage applies heat in a manner that can heat the entire bulk of the barrel metal at a much lower intensity.
This is most easily observed in fully automatic weapons, with propellant heat transfer heating the first few inches from breech forwards and friction of beullet passage heating the barrel closer to the muzzle.

When high temperature double base propellants were used they often heated the breech enough to cook off chambered cartridges. As nitroglycerin contents were reduced, from the high of 58% to the present 7-8% or less the heating of the breech was reduced till automatic weapons firing from a closed breech no longer poses a cook off problem, but barrel overheating remains a factor due to heating by friction of bullet passage.

Studies on heating by bullet friction were done long ago, using hydraulic rams to force bullets through rifled barrels without any heat from propellant gases.
I may have results of these tests saved to documents, but finding them will be a chore I don't wish to get into just now.

Bore heating of spring piston air rifles due to heat generated by sudden compression is a known factor, pre charged pnuematics and CO2 powered rifles on the other hand act to cool the barrel yet these can still sometimes show significant heating of the barrel due to friction if the pellet or bullet has much if any bearing surface to speak of. Waisted air gun pellets are designed to present minimal bore contact precisely because the least friction can greatly reduce velocities.
If you've noticed most air gun pellets do have a thin smear of light oil and you can feel it on your fingers after handling them. Some pellets use a dry lube, sometime impregnated into the surface. Beeman Wadcutters use a dark teflonlike coating, these are my personal favorites.

I've cleaned my opld .22 S&W 78g and was amazed at the amount of lead it had accumulated. I recently obtained a .177 cleaning rod with bronze brush for removing lead from my 177 air rifles. Removing this sort of leading greatly improves accuracy and velocity.
Special felt wads impregnated with cleansing solutions are available for regular cleaning, you fire these like a pellet and they carry away loose fouling, but a bristle brush is necessary to remove more stubborn leading.

[Molly]

Hi Multigunner,
>The Mobillube fiasco that later damaged Springfields involved a very different class of grease with very different properties.

Oh, by all means! But similar physical properties should typically generate similar mechanical effects. Not to beat a dead horse, but the tests you reported interested me.

>Because that shortened barrel allowed enough muzzle blast to mushroom the base of the fired bullets.
>His conclusion on the upsetting in the throat was based on both extrapolation of the effect of pressures at various points in bullet travel and the concave appearance of the bullet bases of those fired from a barrel of normal length.
>The experiment with shortened barrel proved sufficient pressure and acceleration forces remained to continue the upsetting action for a good way up the bore, which is why such continued acceleration can force a bullet to conform to bulged or eroded portions of the bore in the first few inches of travel, but that force drops off as the bullet reached its limit of velocity as it neared the muzzle of a full length barrel. Some pressure remained but not enough to give a sufficient G force of acceleration.

Oh, I have no quarrel with the notion that there is sufficient pressure to produce base upset in the throat with quite a few bullet types and alloys. My concern is whether this actually occurs in reality. As I've said, (and I think you did as well) no bullet can upset beyond the walls of the barrel / bore without blowing the barrel up. Modern cast bullet technology recommends sizing bullets to the greatest diameter that the throat will accomodate. Consequently, one might expect a clearance of perhaps 1/2 mil between most bullets and the throat of the bore, irrespective of absolute diameters. Upset in the bore seems highly unlikely to exceed this value, which would be most difficult to detect after the bullet has impacted a target and been recovered.

It is considerably more likely that any upset that may occur will take place within the case neck. Clearances are notably larger, though not easily quantifiable because of manufacturing tolerances, etc. However, any upset that occurs should result in a foreshortening of the base of the bullet, followed by an immediate resizing as the bullet enters the throat and bore. This resizing should produce a number of observable changes to the bullet. The gas check shank should be at least partially obliterated, much as the heel of a .22 is obliterated by base upset. It will not be protected by the belt of lube around the gas check shank because the lube will be wiped off as the bullet is resized to bore dimensions. Similarly, grease grooves should be expanded and shortened.

I see no such effects from loads with hard alloys, even with loads too powerful for even moderate accuracy.

>If the bullet base is deformed by muzzle blast inaccuracy is the result, just as it would be if the bullet base were deformed by any other means before loading.
Gas checks reduce such damage and allow stronger charges. Card over charge wads also acted to reduce damage to bullet bases and reduce blowby.

I haven't been able to figure out a method of determining exactly what happens at the muzzle with powerful loads. Speculation might include the bullet being literally bent, except that even with wild shooting, I seldom see keyholes. Another mechanism might be base upset as shown in Mann's photos, but my recovered bullets do not show any measureable expansion of the base. I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

>From what you've said you use very light loads and your group sizes indicate that you might get better accuracy with either a slight increase in the load or a slightly softer bullet.

Not so! My initial interest in cast bullets was for big game hunting, and almost all my work was with pretty powerful loads. Accuracy was sometimes horrible before I began to learn how to make good loads, but 100 yard groups eventually settled down at about 1.5 MOA as a typical value for a five shot group. This won't win any bench matches, but is considerably better than necessary for Eastern deer hunting.

>BP target rifles in a similar velocity class printed far tighter groups than you find acceptable. One holer ten shot groups at 200 yards were not uncommon for the .32-40 target rifles of Harry Pope for one example and this without a gas check and only a thin over charge card wad. Those rifles generally used a false muzzle and a sealed blank charge rather than loading as a normal breech loader of course.

Oh, that's not quite true. BP targets from LIGHT loads could indeed exhibit remarkable accuracy, but hunting loads seldom equaled this accuracy. The only light loads I played with were worked up to entertain squirrels. For this, hitting a golf ball at 30 yards was quite sufficient. My guns have been ordinary commercial sporters, not custom built match rifles.

>Sounds like you had a very oversized throat or undersized bullet to begin with to allow that much blowby, a too hard alloy would contribute.

Not that I know of. I invariably sized bullet to the greatest diameter that would enter the throat. In 30 caliber, this was usually 0.312 inches, though it could vary somewhat between rifles. So irregardless of absolute diiameters, throat fit was pretty much a constant.

>Your instance of blowby damage confirms my previous examples of blowby damage when bullets do not bump up to seal properly. Without a proper bullet to bore seal things begin to go wrong quickly.

Perhaps I failed to mention that the blowby damage I reported occurred only with heaver loads, starting at perhaps 30-40 Krag velocities from a 30-06. However, the blowby damage did not reduce with more powerful loads, as should occur if the bullet upset. Instead, blowby progressively increased with the powder weight. These more powerful loads should have been better able to provide whatever upset might have been possible, and produced less blowby. This did not happen. Blowby and damage increased as the load increased.

>You might try a slightly softer bullet or an over the charge card wad if you intend to use such light loads exclusively.

Again, you have apparently misunderstood my goals.

>If your bullets are too hard stepping up the powder charge may not be enough to bump up the bullets enough to form a gas tight seal.

IE, hard cast bullets do not upset in the throat. That's what I've been saying.

>I've fired .36 round balls without lube , when I first began BP shooting in the late sixties. When no lube was used the corners of the grooves showed streamers of lead after the first shot had burned away any preservative grease left in the bore. With even a minimum of lube over the bullets no leading occured at all.

Quite believable! I believe that one of the mechanisms of bullet lubes is to 'contaminate' the surface of the bore and prevent adhesion, just as dirty metal is difficult to solder.

>I've also noted that old military rifles who's bores show the grayish texture of age are less prone to copper fouling than a highly polished bore.
>Makers of modern target rifle barrels have begun to use a similar surface texturing in their barrels to reduce jacket fouling.
>If the pitting s even a tiny bit larger than the near microscopic size then the situation is reversed, with metal fouling increasing greatly.
A seasoned bore may only show a slightly graying of the metal, like an old pocket knife blade. Thats about the optimum for this effect. Any darker and the effect is reversed.

Now THAT's fascinating! I hadn't heard of this at all. What processes are used to provide the surface texturing?

[303Guy]

>I've also noted that old military rifles who's bores show the grayish texture of age are less prone to copper fouling than a highly polished bore.
>Makers of modern target rifle barrels have begun to use a similar surface texturing in their barrels to reduce jacket fouling.
>If the pitting s even a tiny bit larger than the near microscopic size then the situation is reversed, with metal fouling increasing greatly.I've missed a bit but this last comment requires a response. I have a rust pitted, two-groove Lee Enfield that shoots with amazing accuracy and zero copper fouling. I do, however lube the bullet bases (chamfered) with 'waxy-lube' prior to seating. I suspect that small amounts of lube are trapped in the pits and this lubes the next round. Or maybe the pits trap powder soot which does the same thing. But this bore is a little more than 'textured'. It did require fire-lapping though. I also chopped off the last inch or so of barrel and re-crowned it.


These more powerful loads should have been better able to provide whatever upset might have been possible, and produced less blowby.Just a thought on this one .... higher pressure would increase the pressure of the obturating boolit against the bore thus increasing leading damage and possibly creating gas blow-by passages. Just a thought.

I do know that if my paper patch loads in my rust damaged bore Pig Gun are too powerfull the patch pails and leading occurs. Not the streaking type leading one often see's but an even grey deposit of lead throughout the bore and even a star shaped pattern on the muzzle. This with fast powder in a short barrel.

[AriM]

Wouldn't it be prudent to say that obturation being the cause or not, boolits take on the shape of the bore? I think that is proof enough. Maybe I am thinking too simple. I am nowhere near as experienced as the debaters, but plain logic is plain logic. Flow mechanics have not magically changed, have they?

It's amazing how Newton predicted all of these laws and relationships, far before any qualified test equipment was available. They continue to prove out on a daily basis. His observations and generalizations fascinate me.

By these tokens, wouldn't it be safe to assume that some form of obturation is happening. If it's due to powder charge or unequal pressure, does not seem to be important. The bottom line is that the lead deforms during it's travel.

Now isn't it also safe to say, that many tests have proven that something as simple as a crimp die can "obturate" a projectile, before it's even fired?

It would seem to me, that the reason for lead as a primary projectile substance, is due to it's physical property to

1. easily deform
2. retain weight
3. rapidly expand/contract and radiate heat

I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof. The fact that we swage boolits in sizing dies, is simple proof. The fact that we match alloy to pressure is simple proof. The fact that we can recover the projectiles and see etched rifling is simple proof.

Am I missing something that transcends simple logic here????

I think Newton is rolling in his grave.....could some possibly add that as a poll choice?

Sorry for being snarky, just trying to understand.

[303Guy]

Studies on heating by bullet friction were done long ago, ...I have a rust damaged bore 22 hornet with a .223 bore through which I shoot .224 bullets. One day I decided to develope a subsonic load. Well, sometimes the bullet would stop in the bore. These would come out easily. Others made it through and one example came to rest in a non-cotton fabric where it melted itself fast. These bullets also showed heat staining on the copper jacket. I'm not so sure about bullet friction heating the barrel deeper than any other source of heat. I have another story about the hornet - my load used to heat the barrel faster than a high power rifle. Then one day, I increased the powder charge a little and the barrel stayed cool! Go figure. :veryconfu

[Multigunner]

Quite believable! I believe that one of the mechanisms of bullet lubes is to 'contaminate' the surface of the bore and prevent adhesion, just as dirty metal is difficult to solder.

When Cordite was first invented it was found to generate enough heat both by the heat of the gas and friction of increased velocity that copper or cupro-nickel jacket material would fuse directly to the bore steel making it almost impossible to remove. When they were testing another propellant which left more fouling they found that when a cordite propelled round was fired alternately along with the other rounds little or no metal fouling resulted. They found this to be due to carbon fouling insulating the bore steel from direct metal to metal contact.
Afterwards they added a 5% mineral jelly content to the basic Nitroglycerin/Nitrocellulose formula, the mineral jelly producing a thin skin of carbon fouling to reduce metal fouling.
Flake cordite used in pistol cartridges and blank cartridges does not contain mineral jelly.



It is considerably more likely that any upset that may occur will take place within the case neck. Clearances are notably larger
There is some upset while the bullet is still in the case neck, some cartridge/bullet combinations more or less than others. On other threads I've cautioned owners of older military rifles to throughly clean chamber necks of built up carbon and lead that can choke the case neck causing increased pressures.

When the Boers received a shipment of 7mm ammunition loaded in non standard 53mm length cases they had a rash of blown up mausers.
The bullets were upsetting in the unsupported 4mm gap ahead of the throat, with a ring of jacket material being stripped off to telescop over the next bullet fired, greatly increasing pressures.
A stop gap fix was to use a thick grease on the bullets to fill the gap long enough for the bullet to clear it. The incompressible grease acting to slow the expansion of the bullet til clear of the gap.

[303Guy]

When the Boers received a shipment of 7mm ammunition loaded in non standard 53mm length cases they had a rash of blown up mausers.
The bullets were upsetting in the unsupported 4mm gap ahead of the throat, with a ring of jacket material being stripped off to telescop over the next bullet fired, greatly increasing pressures.So, that's what caused those "Kort Nek" blow-ups!


Flow mechanics have not magically changed, have they?No, but we might only be beginning to understand it.


Now isn't it also safe to say, that many tests have proven that something as simple as a crimp die can "obturate" a projectile, before it's even fired?No. Obturate means to seal or block, i.e, obstruct. It does not mean the boolit or bullet deforms, just that it expands enough to seal the bore. Boolit upset means the boolit has actually deformed due to plastic flow. What's wrong with out understanding of Neutonian physics is time. It takes time for metals to undergo plastic deformation. Elastic deformation - which is reversable - can be very fast (and is not permanent).

[StarMetal]

>I haven't been able to figure out a method of determining exactly what happens at the muzzle with powerful loads. Speculation might include the bullet being literally bent, except that even with wild shooting, I seldom see keyholes. Another mechanism might be base upset as shown in Mann's photos, but my recovered bullets do not show any measureable expansion of the base. I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

Now we're talking something that I have a fight in. Specifically shooting the 6.5 Swede at very high velocities with it's exceptionally fast twist. There was a theory here that the alloy bullets bent and flew off into wonder wonder land. One analogy that was given was to chuck a length of copper wire into a variable speed drill and first spin the drill at a low rpm. This would simulate a low velocity alloy load and the wire stays fairly straight. Then spin the wire at a high rpm which would simulate a high velocity alloy bullet and the wire then becomes more like a propeller. Three things wrong with that analogy...1. The barrel isn't holding onto the bullet, it's always moving forward..2. It simply doesn't happen that way...and 3. I proved that wrong with my high velocity accurate shooting of the 6.5 Swede (and I might add other 6.5 calibers with very fast twist) which you may have read about on this forum.

Nope on this one you have are not correct. If the alloy can survive the trip down the bore it's not going to bent at the muzzle nor in flight. It can bent went it encounters an obstacle.

I do believe you are off on pellets not leading the bores of air rifle and I believe Multigunner is in agreement with me there also.

Multigunner is, in my opinion, also correct that there is lots of friction heat created by the bullet in passage through the bore. I've also had heated debated on this in another area of why are casings from a semi auto firearm much much hotter then from manually operated ones. My reasons are because of two things...1. one heat from the powder combustion..and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.

[Molly]

Hi AriM,

>By these tokens, wouldn't it be safe to assume that some form of obturation is happening. If it's due to powder charge or unequal pressure, does not seem to be important. The bottom line is that the lead deforms during it's travel.

You may be failing to distinguish between deformation and obturation. Obturation is a special case of deformation, wherein the base of the bullet is expanded by the pressure of the round, to the limits of the chamber and bore. Deformation is ANY change in shape of the bullet.

>It would seem to me, that the reason for lead as a primary projectile substance, is due to it's physical property to
>1. easily deform
>2. retain weight
>3. rapidly expand/contract and radiate heat

Actually, none of these properties are as important to a bullet's performance as its density. The high density of lead enables it to maintain velocity and flatten trajectory better than most other metals, all else being equal. There are better metals from a performance perspective though: Gold is more dense, and some aristocrats actually had gold bullets for their muzzle loading arms. However, gold is not an optimal choice from other perspectives. (VBG)

>I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof.

Of what? That lead will melt and pour? That's not in question.

>The fact that we swage boolits in sizing dies, is simple proof.

Of what? That lead is maleable? Again, that's not in question.

>The fact that we match alloy to pressure is simple proof.

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.

>The fact that we can recover the projectiles and see etched rifling is simple proof.

Seems to me that any etching remaining on a recovered bullet drive band is ample proof that obturation or expansion did NOT take place, as it would have wiped the etching away.

[felix]

"If the alloy can survive the trip down the bore it's not going to be bent at the muzzle nor in flight". Joe, that's true when the ENTIRE projectile leaves the gun instantaneously. ... felix

[StarMetal]

"If the alloy can survive the trip down the bore it's not going to be bent at the muzzle nor in flight". Joe, that's true when the ENTIRE projectile leaves the gun instantaneously. ... felix

Felix,

I'm finding that my alloy of 50/50 (air cooled I might add) can take far more abuse going down the bore of my 6.5 Swede then many of us have thought. In experimental testing of new loads I found (without dangerous pressures or blowing of primers, etc.) that I had exceeded the speed limit so to say with one load. I had that little Kurtz going over 2800 fps, not stripping in the bore, not leading the bore, and staying on the target paper, alone the whole back stop. More going on here then meets the eye.

You are correct in stating "when the whole projectile leaves the muzzle" and if you can remember the picture I posted a long time ago of a pristine retrieved bullet fired from my Steyr M95 and bullet had raised ridges (past the widest diameter of the bullet) near the pressure or force side of the lands. One would thing "How could that be when it's contained in the bore". Well my answer is we know the bullet is spinning, even when it has entirely left the muzzle, and thus the edge or mouth of the muzzle raised that ridge until it let go of the bullet.

[Molly]

Hi StarMetal

>>I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

>Now we're talking something that I have a fight in. Specifically shooting the 6.5 Swede at very high velocities with it's exceptionally fast twist. There was a theory here that the alloy bullets bent and flew off into wonder wonder land. ... Three things wrong with that analogy...and 3. I proved that wrong with my high velocity accurate shooting of the 6.5 Swede ... which you may have read about on this forum.

No, but I don't doubt you for a moment. In fact, I found the 6.5 Swede to work quite well with high velocity hard cast bullets over a pinch of CoW, despite lacking lube, sizing or gas check.

>Nope on this one you are not correct. If the alloy can survive the trip down the bore it's not going to bent at the muzzle nor in flight. It can bent went it encounters an obstacle.

Nor did I say it did. It was just one speculation among others, presented as something to consider, not as a definitive answer to the problem of what muzzle blast does. I explicitly noted that I had not been able to come up with any tests that would tell me what happens at the muzzle.

>I do believe you are off on pellets not leading the bores of air rifle and I believe Multigunner is in agreement with me there also.

This could be just a semantic quibble. I know that felt wads are used in air rifles, purportedly to remove leading. I think that's delusional. No leading I ever dealt with would be removed by a felt wad, particularly in a single pass. Indeed, some of it could hardly be removed by steel wool, applied vigorously over a long period of time. Now if you want to consider traces of loose lead dust as leading, I can go along with you. But not if you are referring to adherent leading.

>Multigunner is, in my opinion, also correct that there is lots of friction heat created by the bullet in passage through the bore.

Possibly so, but is the heat generated anywhere near the order of magnitude of the heat imparted by the propellent? I'd be surprised! The total heat imparted is less than about 500 or 600 degrees F. If it were more, the bullet would melt in the bore.

>I've also had heated debated on this in another area of why are casings from a semi auto firearm much much hotter then from manually operated ones. My reasons are because of two things...1. one heat from the powder combustion..and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.

May I suggest another thought? The autoloading feature will eject the freshly heated case before it has a chance to bleed much heat to the barrel. A manually operated action will not eject the case until it has had at least a few seconds to dump its heat. As a result, the auto-ejected case still has most of its heat, and is hotter. The manually ejected case has lost a significant portion of its heat, and is cooler.

I've done some actual testing along this line. You can buy thin, wax impregnated paper strips that are calibrated by the melting point of the wax. These strips will fit between a case and the chamber walls. On firing, you can determine whether or not the case reached the temperature of the wax in the strip you tested. If so, use a higher temperature strip next time. If not, use a lower melting strip. I got into this because wax will flow from prressure as well as temperature, and I was trying to develop a pressure measurement system. I got good reproducability, and it was little trouble to duplicate the readings obtained with factory ammo. But there were always questions about the thickness and hardness of the case that cast doubt on the validity of the results. In the end, I gave it up, but it was a lot of fun while it lasted.

[Multigunner]

So, that's what caused those "Kort Nek" blow-ups!



I've seen alternate theories presented, more like hypothesis really since the alternates have no access to the rifles or ammo while the Boers did.

I can only go by the written descriptions, but here is how I see it happening.

When the bullet bumped up on the way out of the case neck the unsupported portion of the jacket swelled into a ring ahead of the case mouth, separating from the core at that point and over stressing the jacket which was likely work hardened from crimping pressures. Breakage of bullet jackets at crimping grooves was a not uncommon problem.
The rear portion of the jacket having broken free with its expanded front edge catching the end of the chamber mouth would strip away from the core, the bullet with blown through section of core then departs, with little chance of hitting anything.
The operator cycles the bolt extracting the empty case but leaving a short section of tube stuck in the chamber neck.
When the next round enters the chamber the bullet telescopes into the tube and wedges firmly, the bullet is pushed back into the case compressing the powder charge.
When we shoot for recreation, if we have difficulty chambering a round we back off and check the chamber, in the heat of battle the shooter would use any means necessary to jam that danged cartridge home.
Since previous military fire arms in use in Africa were often plagued by bent coiled brass cases, verdgris, swollen shotshells, etc, recalricant cartridges were a simple fact of life, and raised no red flag.

When our intrepid warrior finally got that blasted bolt closed and turned home, he now had a oversized projectile jammed deeply into the case, with a tightly compressed charge of an already very powerful cartridge.

I've never seen a good explanation of just how those kort nek 7X53 cartridges ended up in Africa, nor any rifle chambered for such a cartridge.
Theres speculation that the 7mm had originally been intended to use the 53mm case length and these cases had been rushed into production before the specs were finalized, then left in storage till some means of using them came along. If not for the Boers buying up anything that would shoot those short cases would probably have been scrap metal.
The cases may also have been formed from drawn blanks intended for the 7.65X53, with the manufacturer not taking the possible dangers into account.

For whatever reason this incident would indicate that its not wise to use a case thats too short.

I remember that a similar problem has been reported when .38 Super Auto cartridges were fired in a .38 Special or .357 magnum Chamber.
Firing .32 ACP in a .32 S&W long might cause the a pressure rise as well, but not to the same extent since the .32 ACP is such a low pressure cartridge with a stout jacketed bullet.

There are revolvers with chambers reamed in a gentle taper, which allow cartridges of the same general .357/9mm bullet size but cases of varying lengths to be fired safely.

[StarMetal]

Hi StarMetal

>>I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

>Now we're talking something that I have a fight in. Specifically shooting the 6.5 Swede at very high velocities with it's exceptionally fast twist. There was a theory here that the alloy bullets bent and flew off into wonder wonder land. ... Three things wrong with that analogy...and 3. I proved that wrong with my high velocity accurate shooting of the 6.5 Swede ... which you may have read about on this forum.

No, but I don't doubt you for a moment. In fact, I found the 6.5 Swede to work quite well with high velocity hard cast bullets over a pinch of CoW, despite lacking lube, sizing or gas check.

>Nope on this one you are not correct. If the alloy can survive the trip down the bore it's not going to bent at the muzzle nor in flight. It can bent went it encounters an obstacle.

Nor did I say it did. It was just one speculation among others, presented as something to consider, not as a definitive answer to the problem of what muzzle blast does. I explicitly noted that I had not been able to come up with any tests that would tell me what happens at the muzzle.

>I do believe you are off on pellets not leading the bores of air rifle and I believe Multigunner is in agreement with me there also.

This could be just a semantic quibble. I know that felt wads are used in air rifles, purportedly to remove leading. I think that's delusional. No leading I ever dealt with would be removed by a felt wad, particularly in a single pass. Indeed, some of it could hardly be removed by steel wool, applied vigorously over a long period of time. Now if you want to consider traces of loose lead dust as leading, I can go along with you. But not if you are referring to adherent leading.

>Multigunner is, in my opinion, also correct that there is lots of friction heat created by the bullet in passage through the bore.

Possibly so, but is the heat generated anywhere near the order of magnitude of the heat imparted by the propellent? I'd be surprised! The total heat imparted is less than about 500 or 600 degrees F. If it were more, the bullet would melt in the bore.

>I've also had heated debated on this in another area of why are casings from a semi auto firearm much much hotter then from manually operated ones. My reasons are because of two things...1. one heat from the powder combustion..and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.

May I suggest another thought? The autoloading feature will eject the freshly heated case before it has a chance to bleed much heat to the barrel. A manually operated action will not eject the case until it has had at least a few seconds to dump its heat. As a result, the auto-ejected case still has most of its heat, and is hotter. The manually ejected case has lost a significant portion of its heat, and is cooler.

I've done some actual testing along this line. You can buy thin, wax impregnated paper strips that are calibrated by the melting point of the wax. These strips will fit between a case and the chamber walls. On firing, you can determine whether or not the case reached the temperature of the wax in the strip you tested. If so, use a higher temperature strip next time. If not, use a lower melting strip. I got into this because wax will flow from prressure as well as temperature, and I was trying to develop a pressure measurement system. I got good reproducability, and it was little trouble to duplicate the readings obtained with factory ammo. But there were always questions about the thickness and hardness of the case that cast doubt on the validity of the results. In the end, I gave it up, but it was a lot of fun while it lasted.

Molly

Afraid I can't be aboard on the semi auto cases are hotter because they are ejected from the chamber so fast they are still hot. One can shuck a case from the chamber with a bolt gun pretty fast and the case is no ways near as hot at the semi auto. You mean to tell me that the time it takes to bolt a rifle that the heat from the case has dissipated to the rifle? I doubt that much. Look how long semi auto casings stay very hot on the ground. The cooling of the case to air is pretty good being it's exposed to the cooling air both internally and externally.

If you doubt friction can cause that much heat are you aware of welding metal by friction? Also do you have a clue how how the brakes get on an airliner? In the case of the airliner we're talking about thousands of degree....almost instantly.

Nope, you're off on that one. By the way I'd love to see you shoot a Swede at high velocity with some degree of accuracy with a normal alloy without lube or gas checks. That's not crowing on my part, I just find it hard to believe. I know there are some that can shoot bare alloy bullets with success.

[AriM]

Hi Molly,


>You may be failing to distinguish between deformation and obturation. Obturation is a special case of deformation, wherein the base of the bullet is expanded by the pressure of the round, to the limits of the chamber and bore. Deformation is ANY change in shape of the bullet.


this is the basis of my point. i understand the defined differences between "obturation" and deformation. however, I am trying to say that, for whatever reason lead deforms when pushed through the barrel. it seems to me, that this being due to obturation or other "unknows" is moot. why would it make a dramatic difference? again I am oversimplifying and don't want to lead you to believe I don't understand the differences. none the less, the boolit deforms to fit the bore.

>Actually, none of these properties are as important to a bullet's performance as its density. The high density of lead enables it to maintain velocity and flatten trajectory better than most other metals, all else being equal. There are better metals from a performance perspective though: Gold is more dense, and some aristocrats actually had gold bullets for their muzzle loading arms. However, gold is not an optimal choice from other perspectives. (VBG)

well I had hoped that my key point of "ability to retain weight" would follow suit with what you are saying. I do understand that density (hence weight in an appropriate size) is a primary asset of Pb.

>I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof.

Of what? That lead will melt and pour? That's not in question.

>The fact that we swage boolits in sizing dies, is simple proof.

Of what? That lead is maleable? Again, that's not in question.

>The fact that we match alloy to pressure is simple proof.

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.

>The fact that we can recover the projectiles and see etched rifling is simple proof.

>Seems to me that any etching remaining on a recovered bullet drive band is ample proof that obturation or expansion did NOT take place, as it would have wiped the etching away.



your above assumptions, about my statements (hate to be rude, but you did say something about assumptions earlier in this thread) are partially correct. except for the last one.

if obturation occurs then the projectile would take the shape of the bore. lands and grooves. it would be my inclination to believe, that obturation continues to happen even after the boolit leaves the muzzle. that being my theory/analysis the boolit would be etched with the rifling pattern at the very end of the barrel (muzzle). this recovered boolit would show these signs. UNLESS, gas blow-by / flame cutting stripped them off. does this sound logical. i am not trying to post a rebuttal or argument, simply trying to give you an idea of where I am coming from....and hopefully, understand where you are coming from.

Richard Lee wrote (modern reloading 2) that he witnessed lead streaking from a boolit, that was inappropriate for the pressure curve encountered. he goes on to say that he further tested this by charging even higher. the boolit exploded in flight and "broke the windshield of his new barracuda". I think this kind of proves that obturation and deformation continue to occur during the boolits entire travel. my only guess would be that this is due to a jet of hot gasses that follow the boolit, or are generated by a high/low pressure zone in front of and behind the boolit. it all seems to be much more complex than we are all making it out to be.

I personally believe that obturation and deformation are due to specific pressure curve effects on specific alloys. i.e. too little pressure for the boolits hardness, and the boolit will not bump up and seal the bore and will fail in the barrel (at some point). too much pressure and the boolit with bump up, but be followed by a trail of gasses. when the boolit no longer has a surface (harder than it) to expand against (leaves the muzzle) it will also fail (due to gasses).


it is my opinion, based on testing and limited experience, that the alloy MUST match the pressure curve of the charge and all of the associated variables (some of which are unknowns). in this scenario, the boolit bumps to seal the bore. after all we can't really cast boolits with the rifling in them already...(well Lee does make the REAL minnie ball) it's not practical, or worth the time. therefore the boolit (properly sized or not) does obturate, as does a boolit of imperfect size. in any event obturation is critical to stop failure of the projectile (in the ways I described above). I hope this is cogent....

so it seems that no one, has ever offered conclusive proof that any of these phenomenon occur. only speculation based on observation. my observations and understanding of flow dynamics and the effects of pressure on metals (family has been in metalworking for 2 generations, certainly not saying I am an expert) would lead me to believe that obturation DOES occur. that obturation is a form of deformation. it is hard for us to argue that the boolit does in fact deform. from casting, all the way to the target. with MANY points in between.

maybe we are arguing the same point, and it's an issue of terminology. I am still not quite sure what your conclusion is. you believe that obturation does not occur, yet you emphatically state that deformation occurs during the powder expansion/ignition and all along the bore, with many points to illustrate why this happens. ok, fair enough. if a smooth or rough bore cause deformation of some kind (which you agree to) and the projectiles travel to that point of the bore is under the power/pressure of a powder charge and it's associated gasses, wouldn't that be obturation??


P.S. I think that Richard Lee's chapters on this subject (modern reloading 2) are the best explanation of these phenomenon. I don't want to make assumptions, but you have read these chapters (7-10 I believe)? He breaks this down, with limited scientific analysis (i agree that it is not complete) and with countless hours and years of experience. also a lifetime of access to the industry, far beyond what any of us have. I think it's not possible to overlook his findings. He simply is more of an authority on this subject, than all of us combined (IMO). His findings have gone a long way to change some of my opinions of cast boolits and pressure curves. I hope you can offer me proof, beyond Mr. Lee's that he is incorrect. I am eager for you to change my opinions, in the same way Mr. Lee has....let's keep the dialogue going and keep it friendly. We are all on that same team

:cbpour: :lovebooli: :castmine:


P.S.S. this is grossly oversimplified, but it's a definition, none the less (see below)
http://en.wikipedia.org/wiki/Obturate


P.S.S.S (lol) this is your own statement, in rebuttal to mine


>The fact that we match alloy to pressure is simple proof. (Ari)

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.
(Molly)

you say that obturation is possible, probable and DOES happen in your answer....but then later on you say obturation doesn't happen....which one is it?

[StarMetal]

Hi Molly,


>You may be failing to distinguish between deformation and obturation. Obturation is a special case of deformation, wherein the base of the bullet is expanded by the pressure of the round, to the limits of the chamber and bore. Deformation is ANY change in shape of the bullet.


this is the basis of my point. i understand the defined differences between "obturation" and deformation. however, I am trying to say that, for whatever reason lead deforms when pushed through the barrel. it seems to me, that this being due to obturation or other "unknows" is moot. why would it make a dramatic difference? again I am oversimplifying and don't want to lead you to believe I don't understand the differences. none the less, the boolit deforms to fit the bore.

>Actually, none of these properties are as important to a bullet's performance as its density. The high density of lead enables it to maintain velocity and flatten trajectory better than most other metals, all else being equal. There are better metals from a performance perspective though: Gold is more dense, and some aristocrats actually had gold bullets for their muzzle loading arms. However, gold is not an optimal choice from other perspectives. (VBG)

well I had hoped that my key point of "ability to retain weight" would follow suit with what you are saying. I do understand that density (hence weight in an appropriate size) is a primary asset of Pb.

>I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof.

Of what? That lead will melt and pour? That's not in question.

>The fact that we swage boolits in sizing dies, is simple proof.

Of what? That lead is maleable? Again, that's not in question.

>The fact that we match alloy to pressure is simple proof.

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.

>The fact that we can recover the projectiles and see etched rifling is simple proof.

>Seems to me that any etching remaining on a recovered bullet drive band is ample proof that obturation or expansion did NOT take place, as it would have wiped the etching away.



your above assumptions, about my statements (hate to be rude, but you did say something about assumptions earlier in this thread) are partially correct. except for the last one.

if obturation occurs then the projectile would take the shape of the bore. lands and grooves. it would be my inclination to believe, that obturation continues to happen even after the boolit leaves the muzzle. that being my theory/analysis the boolit would be etched with the rifling pattern at the very end of the barrel (muzzle). this recovered boolit would show these signs. UNLESS, gas blow-by / flame cutting stripped them off. does this sound logical. i am not trying to post a rebuttal or argument, simply trying to give you an idea of where I am coming from....and hopefully, understand where you are coming from.

Richard Lee wrote (modern reloading 2) that he witnessed lead streaking from a boolit, that was inappropriate for the pressure curve encountered. he goes on to say that he further tested this by charging even higher. the boolit exploded in flight and "broke the windshield of his new barracuda". I think this kind of proves that obturation and deformation continue to occur during the boolits entire travel. my only guess would be that this is due to a jet of hot gasses that follow the boolit, or are generated by a high/low pressure zone in front of and behind the boolit. it all seems to be much more complex than we are all making it out to be.

I personally believe that obturation and deformation are due to specific pressure curve effects on specific alloys. i.e. too little pressure for the boolits hardness, and the boolit will not bump up and seal the bore and will fail in the barrel (at some point). too much pressure and the boolit with bump up, but be followed by a trail of gasses. when the boolit no longer has a surface (harder than it) to expand against (leaves the muzzle) it will also fail (due to gasses).


it is my opinion, based on testing and limited experience, that the alloy MUST match the pressure curve of the charge and all of the associated variables (some of which are unknowns). in this scenario, the boolit bumps to seal the bore. after all we can't really cast boolits with the rifling in them already...(well Lee does make the REAL minnie ball) it's not practical, or worth the time. therefore the boolit (properly sized or not) does obturate, as does a boolit of imperfect size. in any event obturation is critical to stop failure of the projectile (in the ways I described above). I hope this is cogent....

so it seems that no one, has ever offered conclusive proof that any of these phenomenon occur. only speculation based on observation. my observations and understanding of flow dynamics and the effects of pressure on metals (family has been in metalworking for 2 generations, certainly not saying I am an expert) would lead me to believe that obturation DOES occur. that obturation is a form of deformation. it is hard for us to argue that the boolit does in fact deform. from casting, all the way to the target. with MANY points in between.

maybe we are arguing the same point, and it's an issue of terminology. I am still not quite sure what your conclusion is. you believe that obturation does not occur, yet you emphatically state that deformation occurs during the powder expansion/ignition and all along the bore, with many points to illustrate why this happens. ok, fair enough. if a smooth or rough bore cause deformation of some kind (which you agree to) and the projectiles travel to that point of the bore is under the power/pressure of a powder charge and it's associated gasses, wouldn't that be obturation??


P.S. I think that Richard Lee's chapters on this subject (modern reloading 2) are the best explanation of these phenomenon. I don't want to make assumptions, but you have read these chapters (7-10 I believe)? He breaks this down, with limited scientific analysis (i agree that it is not complete) and with countless hours and years of experience. also a lifetime of access to the industry, far beyond what any of us have. I think it's not possible to overlook his findings. He simply is more of an authority on this subject, than all of us combined (IMO). His findings have gone a long way to change some of my opinions of cast boolits and pressure curves. I hope you can offer me proof, beyond Mr. Lee's that he is incorrect. I am eager for you to change my opinions, in the same way Mr. Lee has....let's keep the dialogue going and keep it friendly. We are all on that same team

:cbpour: :lovebooli: :castmine:


P.S.S. this is grossly oversimplified, but it's a definition, none the less (see below)
http://en.wikipedia.org/wiki/Obturate

I had always wondered if the TC Maxi-Ball indeed did bump up like they said. I started out on tests to find if they did. You now the majority of that bullet fits into the bore quite easily and only the front band on the nose engraves. So finally I was able to retrieve some and they did show rifling on all the bearing bands.

Shooting hollow base bullets too fast, or with too much pressure, blows the skirts off them....we know this.

One final thing we've all heard if you're gangster and you shoot someone just ruin the muzzle (or crown) of your barrel, or even saw off the end of the barrel, it you don't want to get rid of the firearm and forensics can't determine if the bullet was fired from such gun. Meaning the last marks on the bullet are from the muzzle, so even if the bore is larger there, there must be some obturation going on in the entire length of the barrel....in other words constant pressure keeping it obturated.

[AriM]

I had always wondered if the TC Maxi-Ball indeed did bump up like they said. I started out on tests to find if they did. You now the majority of that bullet fits into the bore quite easily and only the front band on the nose engraves. So finally I was able to retrieve some and they did show rifling on all the bearing bands.

Shooting hollow base bullets too fast, or with too much pressure, blows the skirts off them....we know this.

One final thing we've all heard if you're gangster and you shoot someone just ruin the muzzle (or crown) of your barrel, or even saw off the end of the barrel, it you don't want to get rid of the firearm and forensics can't determine if the bullet was fired from such gun. Meaning the last marks on the bullet are from the muzzle, so even if the bore is larger there, there must be some obturation going on in the entire length of the barrel....in other words constant pressure keeping it obturated.



we are essentially on the same page. glad that my points made to Molly (in response to his points made to me) are cogent, and that you were able to follow them. I am no genius. So explaining what I believe to be true can be a little tough to get through (or maybe not).

I think your points made about why semi-auto cases are hotter than a bolt guns (when properly and initially extracted) are very valuable and further prove obturation exists. ESPECIALLY point number 2. You say that you think the cases are hot because of violent extraction and friction. This is proof of obturation. The case mouth expands to fill the chamber (we all know this to be true). The friction of a tight fit, between the chamber and expanded case mouth causes heat under the extraction process. What causes the case mouth to expand? Powder charge and pressure generated by powder charge. What stops it's expansion? The chamber. That is prime evidence of obturation. It is NOT disputable. If it is, it goes against everything believed to be true about case sizing, reloading and fire forming.

Kudos to you for making that remarkable and logical observation.

:drinks:

[303Guy]

... .and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.I would say the frictional heating of the case taking place during firing and not during extraction. The case grips the chamber quite firmly but internal pressure forces it to creap against the chamber walls. Those creap marks are very fomiliar to us. Examine them and on a longer case they can be seen to get shorter toward the neck, where they dissappear. Now thats a huge dose of friction! But the same case is holding the hot and high pressure flame for the entire duration of firing and a lot of heat is going to be transfered to the case. The reason why an auto case is hotter than others is because it is ejected while still hot, thus keeping the chamber cooler. A rapidly operated bolt gun produces way hotter cases than does a slowly operated gun.

But case obturation is due to internal pressure while boolit obturation would be caused by pressure acting on the base which 'attempts' to accellerate the base faster than the nose, causing the body to swell. Barrels also expand under the pressure of firing. This alone could cause the boolit to remain 'tight' in the bore up to the muzzle as the pressure falls and the bore expansion reduces.

But as Molly keeps on stating, it's the 'obturation' of hard alloys that is under question here. We know softer alloys undergo plastic deformation to a lesser or greater degree. Harder alloys cannot deform in the time the pressure is being applied, not plastically, anyway. So, a boolit might obturate elastically without the lube grooves collapsing. Now, all materials can undergo some degree of elastic strain, harder alloys more so than soft lead. Do those boolits 'obturate' elastically or not? Well, yes they do expand radially under the pressure of firing but do they expand enough to 'obturate' the bore? We can actually calculate it! (I use the term 'we' loosely! I've long forgotten the formulae and it's not a simple one. I'm way too lazy to start looking it all up now - it would take me all day).

[StarMetal]

303guy,

Have you ever got a case hot by resizing it fast??? I have.

[AriM]

I would say the frictional heating of the case taking place during firing and not during extraction. The case grips the chamber quite firmly but internal pressure forces it to creap against the chamber walls. Those creap marks are very fomiliar to us. Examine them and on a longer case they can be seen to get shorter toward the neck, where they dissappear. Now thats a huge dose of friction! But the same case is holding the hot and high pressure flame for the entire duration of firing and a lot of heat is going to be transfered to the case. The reason why an auto case is hotter than others is because it is ejected while still hot, thus keeping the chamber cooler. A rapidly operated bolt gun produces way hotter cases than does a slowly operated gun.

But case obturation is due to internal pressure while boolit obturation would be caused by pressure acting on the base which 'attempts' to accellerate the base faster than the nose, causing the body to swell. Barrels also expand under the pressure of firing. This alone could cause the boolit to remain 'tight' in the bore up to the muzzle as the pressure falls and the bore expansion reduces.

But as Molly keeps on stating, it's the 'obturation' of hard alloys that is under question here. We know softer alloys undergo plastic deformation to a lesser or greater degree. Harder alloys cannot deform in the time the pressure is being applied, not plastically, anyway. So, a boolit might obturate elastically without the lube grooves collapsing. Now, all materials can undergo some degree of elastic strain, harder alloys more so than soft lead. Do those boolits 'obturate' elastically or not? Well, yes they do expand radially under the pressure of firing but do they expand enough to 'obturate' the bore? We can actually calculate it! (I use the term 'we' loosely! I've long forgotten the formulae and it's not a simple one. I'm way too lazy to start looking it all up now - it would take me all day).



the formula is BHN x 1422 = appropriate pressure in chamber

or to find the correct BHN for a specific load.....PSI / 1422 = correct BHN

ALL of this info. is available on LASC website and in the Lee Modern Reloading Book (vol. 2).....I don't understand how it can still be an issue?

has everyone read, and understood both those sources??

[303Guy]

Have you ever got a case hot by resizing it fast??? I have. No, I haven't. Interesting! But thinking about it, it's quite logical. Work is being done on the case and work is heat. It's more than just friction though - there is the work of plastic resizing as well. I suppose firing an 'undersized' case such as would be needed in a self-loader, plastic deformation of the case as it expands would be another source of heating of the case.

I wasn't disputing the frictional heating of cases, just saying the friction takes place mostly during firing. There would surely be more friction during extraction, especially if the case is still expanded against the chamber wall.:drinks:

[felix]

AirM, the 303Guy is entirely correct. The formula you are referring attempts to calculate where the expansion is destructive, meaning outside of the plastic phase. Most lino type boolits are shot within the plastic phase and they will distort for a short time allowing obturation, but return to normal after all is said and done. ... felix

We have coined the term "tough lead" to indicate a good returning boolit. Decrease the amount of tin in lino (adding significant lead), the toughness of the boolit can go away allowing permanent destruction. Therefore, lesser pressure, or pressure timing, is mandatory to keep the projectile in the plastic stage. ... felix

Increasing the tin content will also make the boolit loose toughness because of the surface tension parameter as discussed earlier. ... felix

[AriM]

AirM, the 303Guy is entirely correct. The formula you are referring attempts to calculate where the expansion is destructive, meaning outside of the plastic phase. Most lino type boolits are shot within the plastic phase and they will distort for a short time allowing obturation, but return to normal after all is said and done. ... felix

We have coined the term "tough lead" to indicate a good returning boolit. Decrease the amount of tin in lino (adding significant lead), the toughness of the boolit can go away allowing permanent destruction. Therefore, lesser pressure, or pressure timing, is mandatory to keep the projectile in the plastic stage. ... felix

Increasing the tin content will also make the boolit loose toughness because of the surface tension parameter as discussed earlier. ... felix

oh of course. I am not disputing that he is correct. I am disputing, how the question of obturation, can even be an on going question at all. i can't see any evidence or conclusive proof that boolits do or do not obturate. I am under the understanding, that the general accepted conclusion (by industry giants) is that boolits do obturate. not just soft ones, but any boolit that is subjected to pressure (of course to a greater or lesser degree, than the CORRECT combination). the issue of rotational obturation is also completely logical and widely accepted. is it not?

I am just curious how a thread on this subject can reach 11 pages. it would seem that this subject has been moot and generally accepted for many decades.

am I missing some massive bit of information, that shows otherwise?

obturation happens from the beginning of the process to the end, correct?

when the boolit leaves the muzzle, it continues to obturate, due to the gasses propelling it. those gasses don't have anywhere to go, other than out the muzzle with the boolit. the boolit does not have enough velocity from the initial blast to continue out of the bore correct? if it did squib loads would be non existent.

again, I am asking questions....not drawing lines in the sand. I want to know how this can be an ongoing issue. the science is complex, and seems to be incomplete. however, the logic and observations and countless stages of trial and error (over many decades) would all point to the conclusion, that obturation is in fact an effect and it happens. even the hardest boolit, will obturate to some degree, with a grossly inadequate load. Mr. Lee dedicates many pages to this very subject in his book. it is the most tested and cohesive explanation I have seen. I just don't see how anyone here can claim that they know something that is so overwhelming, that it invalidates Mr. Lee's perfect explanations of the subject.

:Fire:


I think the question that should be asked, is more along the lines of : "what constitutes obturation, and is it a proper definition (by today's standards)"

if obturation is the bumping of a boolit because of the effects of powder expansion, gas expansion and detonation. then obturation is an effect that continues through most of the boolits travel, to the destination?

it just seems to me that this is a debate about semantics and an incomplete understanding or incomplete definition of the term. we are all spinning it one way or another (pun?), but all understand the same concepts and accept them.

The current definition seems to have a duality to it. it says that obturation is the bumping of the boolit to seal the bore, before the rifling is engaged. it then goes on to say that this is due to the gasses created and pressure created by the charge. it then seems to end there. that is incomplete (IMO), since the gasses deform the boolit through it's entire travel (since no barrel is perfect). it's really a poorly defined word. maybe that is what the debate is about, and not the effect. I notice that Mr. Lee does try to stay away from the word in his text. yet describes the same thing (essentially).

am i totally misunderstanding the term? or is what I am try to articulate not being put forth in a cohesive/cogent manner?

I am curious how the OP (who I know from other forums and off this site) can ask this question. he is a smart guy and I want to know what lead him to create this poll. instead it seems that it's just an ongoing debate, about semantics.

I am really trying to gain some understanding, beyond what I think I already know. I am open to any and all thorough explanations. I have far less experience than most of the people posting here, but trust what I have read from Mr. Lee and a few other "qualified" professionals. Not just because I read it, but because I have followed their advice, and seen the results myself.

[303Guy]

I am just curious how a thread on this subject can reach 11 pages.That is easy to explain - it's because there are bunch of experienced, intelligent and curious folks who enjoy a good debate, especially when there are new angles and ideas added along the way. It's no so much learning about 'obturation' but rather discovering how much other folks really do know. I like to think I have learned a lot from it all. It's cirtainly taken me along a new path of patched load development by increasing my understanding of what's going on in a bore when a gun is fired.

I have just tested two loads for my Pig Gun; one produces higher chamber pressure but does not disintegrate the patch, so there is insufficient 'obturation' (shotgun powder). The other, with a slower powder (H4227), produces a higher velocity with lower chamber pressure and disintegrates the patch. Is this not along the lines of what you are saying, AriM?

As to why Russel started this thread - he's already told us. He had nothing else to do that evening!:mrgreen:

[AriM]

That is easy to explain - it's because there are bunch of experienced, intelligent and curious folks who enjoy a good debate, especially when there are new angles and ideas added along the way. It's no so much learning about 'obturation' but rather discovering how much other folks really do know. I like to think I have learned a lot from it all. It's cirtainly taken me along a new path of patched load development by increasing my understanding of what's going on in a bore when a gun is fired.

I have just tested two loads for my Pig Gun; one produces higher chamber pressure but does not disintegrate the patch, so there is insufficient 'obturation' (shotgun powder). The other, with a slower powder (H4227), produces a higher velocity with lower chamber pressure and disintegrates the patch. Is this not along the lines of what you are saying, AriM?

As to why Russel started this thread - he's already told us. He had nothing else to do that evening!:mrgreen:



yes we are for sure on the same page about the issues. I still think that the term "obturation" is incompletely defined. It makes the assumption that obturation "ends" after the boolit engages the rifling. this would be plausible if you had an absolutely consistent, perfect barrel. you and I know that this is impossible. not just because of manufacturing limitations, but (as you stated very well) the expansion of the barrel. which is totally inconsistent, and dependent on so many conditions (external and internal) and also let's not forget harmonic resonances. which will be different from shot to shot (humans aren't a vice).

so it seems to me that "obturation" (being the bumping of the boolit by pressure/gas to fill the bore) does not in fact end once the rifling is engaged.

I think more and more, this thread is re-enforcing what Mr. Lee has to say, but I also see two camps here.

As far as "Russel" is concerned. I know for a fact that he didn't do this on a whim. I know him on other forums, and via email....and this thing about obturation being a myth, is something he is big on. Not just a whim because he was bored. I am calling you out Brad (lol). I wanna know what you really think about it and why. You are a smart dude, and I wanna know what is going on in your head, that makes you think obturation is a myth.

I have to say, that Star Metals theory about friction generating excessive heat in auto loaders is a fantastic learning point. I would have never thought of it. Maybe it's not such a bad thread. However, may god have mercy on the word "obturation" :bigsmyl2:

I see some serious gaps in it's definition....

I was actually thinking today (after this thread) of building a clear acrylic tube. then chambering it to fire projectiles softer than acrylic (think nerf ball). The charge could be compressed air. That way it could be scaled up and the math could be done to scale up the load (to match pressure and hardness ratios). This would be an easy device to read pressure on (simply use a regulator gauge). They a camera could be set-up to record the travel of the projectile, through the clear barrel. If the camera was at a high frame rate, the footage could be slowed down and the obturation of the projectile could be witnessed. I think this would be a great thing to do. I think it could help a lot of neophyte casters/reloaders really understand the dynamics, and critical ratios that go into a correct load. Who knows in the process I might totally blow my own theories out of the water (or should I say tube)

[smilie=p:

[felix]

Obturation is actually a medically used term for stopping up wild blood vessels during operations. It actually means to "plug up the pipe so it won't bleed". If we had no expansion going on, and the boolit is a tough one indeed, then leading is almost sure to follow when the elastic limit has not been reached and HELD to the end of the barrel. Thankfully, boolits are not that tough. But, not thankfully, hardness and toughness do not necessarily go together, so its hard to measure if a boolit will lead the barrel or not at a certain velocity. We then are talking shear strength of the lead (alloy). That is somewhat related to the thread herein, but it is hard to pin it down in relation to toughness and hardness. Boolits have to be shot to see what application they are best suited. Suited to BR, tin cans, hunting, etc. ... felix

[Molly]

Hi StarMetal

>Afraid I can't be aboard on the semi auto cases are hotter because they are ejected from the chamber so fast they are still hot. One can shuck a case from the chamber with a bolt gun pretty fast and the case is no ways near as hot at the semi auto.

Yes, but I don't think a bolt action will eject anyhere near fast enough. Try this: Take a semi and a bolt to the range, and just see if you can clear the bolt before the semi can put off 4 or 5 rounds. If you can, my hat is off to you as one of the fastest bolt manipulators I know of.

>You mean to tell me that the time it takes to bolt a rifle that the heat from the case has dissipated to the rifle? I doubt that much.

Well, I really don't have any definitive information here, but you might reflect on the speed at which events occur in the bore of a rifle. A thick steel barrel can be heated in a single shot lasting only perhaps a couple thousandts of a second. I suspect that the same shot will have little difficulty heating a much thinner and less massive brass case to an even higher temperature. Now take that blistering hot case and eject it rapidly. I can tell you from personal experience that the freshly ejected case from even a low pressure round like the 45 ACP is able to peel the skin off of your chest, should you be unfortunate enough to catch it. But if it misses your neck, it will be cooled enough to be handled by the time it has bounced a time or two.

>If you doubt friction can cause that much heat are you aware of welding metal by friction?

Oh, I am aware of frictional welding, though I have zero experience with it. I just doubt that it plays a significant role in this situation. I've been wrong before, and it wouldn't surprise me greatly to be wrong again. But like the fellow from the deep south, I'd like to see some evidence - and not just theories or speculations - before I accept the notion.

>By the way I'd love to see you shoot a Swede at high velocity with some degree of accuracy with a normal alloy without lube or gas checks. That's not crowing on my part, I just find it hard to believe. I know there are some that can shoot bare alloy bullets with success.

Well, it really isn't so hard to do. Start well below maximum loads, and add a volume of Cream of Wheat that is roughly equal to the volume of the neck and shoulder. Take up the extra space in the chamber / case with a pinch of cotton.
Start with midrange loads to get the feel of it, and to develop confidence. Now simply increase your load as prudence would suggest, never going beyond reloading manual maximums for a similar jacketed bullet.

Give the rifle a few shots to condition the bore before each session. I find notably reduced accuracy if the bore is wet or greased. How much accuracy? Well, you aren't likely to win any matches with them, but the accuracy is more than adequate for routine applications like deer hunting. All my records are packed away, but I seem to recall typical accuracy in the range of 2 to 3 MOA groups from my Sweds.

You may encounter problems closing the bolt with your first loads. This happened to me until I traced it to an oversized neck due to the unsized bullet. Depending on your mold, you may see it too. If so, just size the bullet, and otherwise use it without lube or gas check. You will be gratified by the bright clean bore these loads produce. They will also function with squib loads, but too light a load can result in a CoW plugged bore that will try the patience of a saint to remove. I speak from experience.

[AriM]

Obturation is actually a medically used term for stopping up wild blood vessels during operations. It actually means to "plug up the pipe so it won't bleed". If we had no expansion going on, and the boolit is a tough one indeed, then leading is almost sure to follow when the elastic limit has not been reached and HELD to the end of the barrel. Thankfully, boolits are not that tough. But, not thankfully, hardness and toughness do not necessarily go together, so its hard to measure if a boolit will lead the barrel or not at a certain velocity. We then are talking shear strength of the lead (alloy). That is somewhat related to the thread herein, but it is hard to pin it down in relation to toughness and hardness. Boolits have to be shot to see what application they are best suited. Suited to BR, tin cans, hunting, etc. ... felix

yes, I have actually found more than a few definitions for the term. however, the definition in most online dictionaries (when relating to firearms) does say

"obturation refers to the process of a bullet or pellet, made of soft material, flaring under the pressure of firing to seal the bore and engage the barrel's rifling." they all seem to follow that description. the key element being that the boolit bumps until it engages the rifling. that seems very incomplete to me, and leaves a lot of thing unaccounted for. I am not sure that it is just simple semantics here. It is a suggestion, that obturation stops, once the rifling is engaged. I can't get on board with that. Seems that most of us feel that way. Even if we say it a different way.

I think that shear strength is a very valid discussion, and I really do like your point about toughness vs. hardness. They should not be confused. Linotype is certainly hard, but certainly not tough. It would be a horrible projectile for steel targets. Even if it was loaded to the correct pressure. Equally bad for game. So again your points are great and inline with the accepted standards (and I would expect no less from someone of your experience).

I think that there are many unknowns to be discovered, but "obturation" (in it's clinical understanding) seems to be a freeway system, that leads to the same end. It happens. Physics does allow for compression of solids. I made this point many months ago (maybe on page 6 or so of this thread). The only reason we have to say certain states of matter are or are not compressible is to fit standards based table and calculations.

In fluid dynamics, we have to assume that fluid is not subject to compression, or we would never have a standard to base our variables around. This works for mechanical sciences and for statistics, but it violates basic Newtonian physics. It also assumes that there is no unifying theory to be had. I digress.


I think the real topic to debate/discuss/ponder collaborate on here, is more related to the extent that obturation (in it's clinical definition) extends. In my opinion and based on my own tests and research and readings. Obturation can also be married to external ballistics. Or in lay terms. I don't end when the little lead thingy hits the rifling :bigsmyl2:

[StarMetal]

Molly,

22 rimfire cartridges don't have enough powder in them to make them skin burning hot, but yet casing shucked out of an auto loader with burn you.

Listen to this true story. One of my really good friends had a Rem 742 in 30-06 many years ago, which by the way shot groups that most bolt actions would have a hard time beating. He loaded it using the Lee hand loader. Yes you read right, a Lee hand loader and using the rounds in a semi auto. So here we have a tighter fitting cartridge then a fully resized one or factory round. He shot three shot groups with it. Starting with a cold rifle he fired three shot and remember he had the magazine full. Left the rifle in the sand bags and we walked up to the target to look it over. When we got back we noticed one the ejected cartridge had melted all the way through the styro foam cartridge containers that Remingtom loved to use. We noticed the other empty casings were a deep blue from heat, I'm talking about like gun bluing and this was from the case mouth to about halfway down the case. The rifle didn't do this with factory ammo or fully resized ammo. Now you tell me that's not friction heat. That cold rifle also wasn't going to get the barrel hot enough either to warm your fingers on, which it didn't.

[felix]

Everything compresses somehow, sometime if the following holds water: A "black hole" location is a FINAL resting place for all matter in its magnetic neighborhood. ... felix

[AriM]

Everything compresses somehow, sometime if the following holds water: A "black hole" location is a FINAL resting place for all matter in its magnetic neighborhood. ... felix

actually the newest school of science/physics, is saying that no true singularity exists. Rather the event horizon is comprised of many smaller/less dense singularities orbiting a larger central mass. The proof of this is fluctuations in gravity pulse measurements. Gravity waves if you will. The theory states that gravity propagates faster than light. In wavelengths so long, that we can't measure them, yet. Very soon the gravity wave observatory will go into service. It is comprised of 3 probes, spread across immense distance. They are used to triangulate point of origins of gravity pulses (that is the theory anyhow).

Wow talk about off topic. You are a smart guy Felix. I like reading your posts and replies. They make me think.

So I pose this question. Since all matter compresses, obturation does occur to some degree, ANYTIME mass meets pressure meets density. It might be minimal, but it is a constant state of flux. This is where Mr. Lee's writings end, and my own opinions begin. It is also quite possible, that I am just an idiot. Who knows? It's all relative.

what's yer point of reference?

[smilie=s::brokenima

[Multigunner]

Well in the words of Al Bundy "in Wanker County everything is relative", that goes for fluid compressibility as well. Fluids aren't truly incompressible, they are relatively incompressible compared to other substances.
First real world example I remember studying was the use of gasoline in the bouyancy tanks of deep diving bathyscapes. Gasoline is lighter than water but relatively incompressible, so water pressures of a great many atmospheres had little effect on the structure of the tank. If air had been used the tank would have to be built like a bank vault to withstand the pressures.

The only real question about obturation is not if it happens but how. Theres no all encompassing answer to that, due to the very wide range of bullet types and power levels involved.

Now as to gas pressure itself, without resistence there'd be nothing to work against. In part resistence can be friction or mechanical force required for engraving of the bullet. This holds with most breechloaders, but would not explain the Pope style false muzzle loading rifles with seperate propellant cartridge. With those rifles the bullet is pre engraved before any gas pressure is applied and not forced into a tighter throat. So obturation in this instance requires a different source of resistence, purely a matter of inertia of the heavy bullet resisting the application of a motive force.
Hold a water balloon in your hand, raise your hand quickly, and the balloon wil fore shorten and expand evenly in circumference at its equator. The molecules are forced against each other.
Under great pressures metal can flow like a fluid, just as it would if heated to the melting point. Ice at the bottom of a glacier can remain a crystaline solid yet still the glacier flows like a very slow river.

Most confined propellants deliver a greater thrust on initial ignition than later in the burning cycle, mainly due to overcoming initial resistence. But the application of force seldom stops there. The propellant charge will continue to apply force to accelerate the projectile, and the G force of acceleration so long as it lasts will continue to result in the fore shortening and expanding action, forcing the bullet body into the grooves.
When a bullet is driven down a badly eroded bore it can reach portions where the inside diameter is greater than it was at the throat. If the bullet can still expand to fill the grooves all well and good, but if the force of acceleration has dropped off then blowby results heating the surface of the bullet , which can result in jacket separation or in the case of cast a melting and softening with loss of surface integrity, leading to leading and skidding in the grooves and further blowby.

If the bore is rough due to corrosion or built up fouling a bullet that has lost impetus through blowby can seize in the bore at the next constriction and blow through. I've seen a blown through lead bullet before, stuck midway in a discarded rifle barrel.
In the old days stuck bullets were disolved in place using mercury as a solvent, the main mass of the bullet drilled out using a drill softer than the bore steel and the barrel plugged with some mercury inside to soften or disolve whatever was left in the grooves.
A bore that bad would generally require lapping to put it back in usable shape, or more often be discarded.

Blown through jacketed bullets were usually forced out by various means. The 1903 220 gr .30 bullets shed jackets so often a jacket removal tool was issued at one point, intended for every cleaning kit. It was in the form of a mild steel cylinder that fit on the end of a rod, with negative image of the bore and beveled leading edges to pry the stuck jacket out of the grooves.
Once milder propellants were adopted for the .30-06 the tool became a very limited issue item, seldom needed.

Very light loads of fast powders may only apply significant acceleration forces for the first few inches of the bore, past that point the bullet is left to more or less rattle its way to daylight, with increasingly looser fit to the rifling as it goes. The small charge having burned out early on won't cause much noticable blowby, the volume of gas being small.

Experiments with extremely long .32 S&W barrels formed by welding lengths of barrel liners together into barrels about ten feet long or longer, I forget the exact length. Allowed the experimentor to find out exactly when the small charge exhausted its ability to accelerate the bullet, and measure effects of friction on the bullet once the propellant had been exhausted. At maximum length the bullets either stopped or just fell out the muzzle. The barrel was cut back in increments and velocity measured at each stage.
Similarly tests on early production CCI Stinger and Viper cartridges, when they first began showing up on the US market at least, indicated these were optimised for the very short barreled trappers guns popular in Canada , and this made them a good choice for handguns.
Testing showed the cartridges gave maximum velocities from a 16 inch barrel with velocity dropping at barrel lengths over 16 inches. Short barreled .22 rifles were very popular items at the time, and still are to some extent.
The fast acceleration and quick burn out of those cartridges meant they were less efficient in traditional longer barreled .22 rifles, velocity wise at least, but there was next to no influence on the bullet exiting the muzzle, since there was little to no muzzle blast as such.

Well thats a wordy and to some extent repititious post, repeating much of what I said earlier.

It occurs to me that a few drawings would explain the mechanism of obturation far better than all the posts on this thread.

[Molly]

Hi Starmetal

>22 rimfire cartridges don't have enough powder in them to make them skin burning hot, but yet casing shucked out of an auto loader with burn you.

Interesting. Did you just say that a 22 doesn't have enough powder to make the cases hot unless they are fired from an autoloader? No, I know you didn't, but that's what I got on the first reading. (VBG) What you say is still not inconsistent with my proposal that the auto-ejected case simply doesn't have time to cool before it hits your skin.

Enough about my mental excentricities. You have claimed that the real cause of hot cases is friction from the chanber walls if I understand you correctly. Why not actually test the notion? Fire something (22 or 30-06, I don't care) and find some way to test case temperature. Maybe it'll melt into a block of parriffin. Or styrofoam. Whatever. I don't care how you test the temperature, just test it. Then wax a few rounds and see if the reduced friction is detectable in whatever temperature test you come up with.

You can even fire two nearly simultaneous shots from your autoloader, pick up the cases and judge temperature with your hands. (Fire the unwaxed case first, so there won't be any residue to confound your results.) I'm betting there won't be any detectable temperature difference between the two cases, despite what should be a substantial reduction of friction.

>Listen to this true story. One of my really good friends had a Rem 742 in 30-06 many years ago, which by the way shot groups that most bolt actions would have a hard time beating. He loaded it using the Lee hand loader. ...When we got back we noticed one the ejected cartridge had melted all the way through the styro foam cartridge containers that Remingtom loved to use. We noticed the other empty casings were a deep blue from heat, I'm talking about like gun bluing and this was from the case mouth to about halfway down the case. The rifle didn't do this with factory ammo or fully resized ammo.

I'd sure like to know why not. Factory, unsized or fully resized makes no difference: When the round is fired, all of them will be clinging to the chamber walls with all the force that the propellent can exert. Sizing or lack thereof normally makes absolutely no difference except in ease of chambering. Under factory 30-06 pressures, that brass case had all the structural resistance of a bit of tissue blowing in the wind.

>Now you tell me that's not friction heat.

I just did, at least in my opinion. Your story - though interesting - seems to have some logical inconsistencies, and lacks some easily performed tests on its validity.

Now may I tell you what I suspect may have been happening? I wasn't there, and can't possibly know for sure, but I've seen some very strange things done by begining reloaders using beginner tools like the Lee Loader. One of these brethern poured his powder out on a sheet of paper and scrapped up a pile of gunpowder that "looked big enough". This was then decanted into a case and topped with a jacketed bullet. Enough said?

As an aside, this in no way refelcts poorly on the Lee Loader. They can produce excellent ammo, and I still have several in my own inventory. When I just want a couple of rounds to test some notion, they are better suited than my Dillon presses.

I've also seen brass cases discolor toward blue from serious overloads. The worse the overload, the deeper the blue. I think that's enough said too.

Now I REALLY don't mean to belittle either you or your friend. God knows, the idiocies that I performed as a beginner don't give me any leeway to make fun of anyone else. It takes a special kind of fool to see if he can fire a 35 caliber bullet through a 6.5mm bore. (Believe it or not, it CAN be done, but I sure don't recommend it!) And I suspect that I've made just about every mistake that it is possible to make with cast bullets. But I honestly think that you have simply misinterpreted what you have seen.

Firearms can do some very strange things. My father swore to me that he had once seen a 30-06 barrel which had the bullet depart the bore about halfway down the barrel. And he was an aircraft gunnery sargeant at the time, and would have had ample opportunity to see strange things.

An interesting test you might try just occurred to me. Find an automotive garage that has a hydraulic press, with an owner that will indulge you for a few minutes. Cut the base from a 30-06 case, and slit it down the side so you can unroll it into a sheet of brass. Drill an attachment hole in one end and place it in the press under some pressure. Lacking a press, put it under a three foot stack of bricks, and then under a six fooot stacn of bricks. Pull the brass sheet out and check the temperature. Then double the pressure and test it again. I'm willing to bet heavily that within the limits of your ability to pull the brass sheet out, you won't find any differences in temperature.

[AriM]

This holds with most breechloaders, but would not explain the Pope style false muzzle loading rifles with seperate propellant cartridge. With those rifles the bullet is pre engraved before any gas pressure is applied and not forced into a tighter throat.

Well thats a wordy and to some extent repititious post, repeating much of what I said earlier.

It occurs to me that a few drawings would explain the mechanism of obturation far better than all the posts on this thread.



Are Pope and Schutzen rifles the same thing?

All of our replies have been wordy repetitions of the same thing. That was my overlying point. We all get it, but explain it a different way. Which leads me to believe that the word "obturation" itself is not fully defined. We need a more thorough word.

On the issue of drawings, did you read my post (a few posts back) about the acrylic, simulated barrel. I think building that and making the information available, would really help a lot of folks. Please go back and read it, and tell me you opinions. I would need help doing the math, to recalculate correct pressure ratios. I do have a lot of the parts necessary to build it though. Including the acrylic tubing.

[StarMetal]

Hi Starmetal

>22 rimfire cartridges don't have enough powder in them to make them skin burning hot, but yet casing shucked out of an auto loader with burn you.

Interesting. Did you just say that a 22 doesn't have enough powder to make the cases hot unless they are fired from an autoloader? No, I know you didn't, but that's what I got on the first reading. (VBG) What you say is still not inconsistent with my proposal that the auto-ejected case simply doesn't have time to cool before it hits your skin.

Enough about my mental excentricities. You have claimed that the real cause of hot cases is friction from the chanber walls if I understand you correctly. Why not actually test the notion? Fire something (22 or 30-06, I don't care) and find some way to test case temperature. Maybe it'll melt into a block of parriffin. Or styrofoam. Whatever. I don't care how you test the temperature, just test it. Then wax a few rounds and see if the reduced friction is detectable in whatever temperature test you come up with.

You can even fire two nearly simultaneous shots from your autoloader, pick up the cases and judge temperature with your hands. (Fire the unwaxed case first, so there won't be any residue to confound your results.) I'm betting there won't be any detectable temperature difference between the two cases, despite what should be a substantial reduction of friction.

>Listen to this true story. One of my really good friends had a Rem 742 in 30-06 many years ago, which by the way shot groups that most bolt actions would have a hard time beating. He loaded it using the Lee hand loader. ...When we got back we noticed one the ejected cartridge had melted all the way through the styro foam cartridge containers that Remingtom loved to use. We noticed the other empty casings were a deep blue from heat, I'm talking about like gun bluing and this was from the case mouth to about halfway down the case. The rifle didn't do this with factory ammo or fully resized ammo.

I'd sure like to know why not. Factory, unsized or fully resized makes no difference: When the round is fired, all of them will be clinging to the chamber walls with all the force that the propellent can exert. Sizing or lack thereof normally makes absolutely no difference except in ease of chambering. Under factory 30-06 pressures, that brass case had all the structural resistance of a bit of tissue blowing in the wind.

>Now you tell me that's not friction heat.

I just did, at least in my opinion. Your story - though interesting - seems to have some logical inconsistencies, and lacks some easily performed tests on its validity.

Now may I tell you what I suspect may have been happening? I wasn't there, and can't possibly know for sure, but I've seen some very strange things done by begining reloaders using beginner tools like the Lee Loader. One of these brethern poured his powder out on a sheet of paper and scrapped up a pile of gunpowder that "looked big enough". This was then decanted into a case and topped with a jacketed bullet. Enough said?

As an aside, this in no way refelcts poorly on the Lee Loader. They can produce excellent ammo, and I still have several in my own inventory. When I just want a couple of rounds to test some notion, they are better suited than my Dillon presses.

I've also seen brass cases discolor toward blue from serious overloads. The worse the overload, the deeper the blue. I think that's enough said too.

Now I REALLY don't mean to belittle either you or your friend. God knows, the idiocies that I performed as a beginner don't give me any leeway to make fun of anyone else. It takes a special kind of fool to see if he can fire a 35 caliber bullet through a 6.5mm bore. (Believe it or not, it CAN be done, but I sure don't recommend it!) And I suspect that I've made just about every mistake that it is possible to make with cast bullets. But I honestly think that you have simply misinterpreted what you have seen.

Firearms can do some very strange things. My father swore to me that he had once seen a 30-06 barrel which had the bullet depart the bore about halfway down the barrel. And he was an aircraft gunnery sargeant at the time, and would have had ample opportunity to see strange things.

An interesting test you might try just occurred to me. Find an automotive garage that has a hydraulic press, with an owner that will indulge you for a few minutes. Cut the base from a 30-06 case, and slit it down the side so you can unroll it into a sheet of brass. Drill an attachment hole in one end and place it in the press under some pressure. Lacking a press, put it under a three foot stack of bricks, and then under a six fooot stacn of bricks. Pull the brass sheet out and check the temperature. Then double the pressure and test it again. I'm willing to bet heavily that within the limits of your ability to pull the brass sheet out, you won't find any differences in temperature.

Molly,

I can assure you my friend is a very careful reloader and those loads weren't overloads. We had a chronograph with us too I'll have you know. How hypocritical of you to come back and say that because you really don't know a reason why it happen. It happen because the cases were only neck size and I believe perhaps the bolt opening sequence may have been out of timing a little and being the cases were about chamber size to begin with being neck sized only they were still obturated to chamber walls and extracted forceably adding to the heat of the case in addition to the powder combustion.

Let me clear some things up for you. I never meant that friction solely is responsible for all the heat in the case. Another hypocritical thought on your part to think that I am so foolish as to thing that. This also applies to the 22 case not burning enough powder to make the case searing hot.

Still waiting for your explanation and response on the tremendous heat generated on airline brakes which is beginning to become a problem for engineers to design a brake out of a material that will hold up.

Maybe your childhood experience in firearms and reloading (which I doubt that you were that young when you say you starte) have diluted your mind to delusion of grandeur.

Regards Pal

[303Guy]

actually the newest school of science/physics, is saying that no true singularity exists. I have long thought this. Umm... this does relate to obturating lead alloy somehow, right?[smilie=1: :mrgreen:

So, should we not find a more suitable word for the expanding boolit. Do we all understand 'upset' to mean lateral plastic deformation of the boolit?

Just a thought on why a boolit should 'uset' laterally without crushing the lube grooves - compressing or stretching a body does not result in tensile or compressive deformation, rather it results in shear at an angle, something like 45° (in a ductile material, anyway). This is why the shear strangth and the compressive strengths are not the same. This means that an 'upsetting' boolit would deform laterally a lot more than axially. (I've only just realized this!):idea:

[StarMetal]

Was out shooting today and when checking my target I looked over the dirt in the backstop and found this 50 caliber Maxi-Ball I had shot back in BP season. Here it's pictured with an unfired Maxi-ball and you can see how the fired one was really compressed. The cam didn't pick it up, but there's rifling on the entire bullet. Appears the front groove section compressed the most. I lube the entire bullet. Being it's not deformed from hitting the dirt I assume this compression took place in the bore.

http://i245.photobucket.com/albums/gg51/starmetal47/MaxiBall-1.jpg

[303Guy]

That's interesting, thanks StarMetal. I would rule out some compression during the decceleration in the dirt but the shortening of the base groove would be bore related, I should think. And that's with lube support. Of course, lube would be being smeered out along the length of the bore - or would it?

According to my 'theory' the lateral expansion should be about equal to the axial compression. It does kinda look that way.

[StarMetal]

That's interesting, thanks StarMetal. I would rule out some compression during the decceleration in the dirt but the shortening of the base groove would be bore related, I should think. And that's with lube support. Of course, lube would be being smeered out along the length of the bore - or would it?

According to my 'theory' the lateral ezpansion should be about equal to the axial compression. It does kinda look that way.

I believe it was a soft landing in the backstop dirt. Not enough nose deformation. Both the base lube groove and the large front lube groove were full of lube. We're talking BP here and probably around 14-1500 fps.

[303Guy]

Ah! A thought!:idea: Lube in the grooves could have supported the boolit - the volume of the grooves would remain the same if the boolit expanded laterally and compressed axially! It makes me wonder whether BP shooters insist on pure, soft lead due to it's properties of deforming uniformly? An alloy that is soft enough to deform with black powder might do so unevenly - I've seen that for myself (not with black powder).

Deformation from hitting the dirt would show up as a tapering of the boolit body. That's not evident here.

[Multigunner]

Are Pope and Schutzen rifles the same thing?


Not exactly, Pope made a great many rifles, some in the Schutzen style more or less, but the schutzen is a European target rifle, predating the cartridge era. Some schutzens use the false muzzle along with a blank, but some loaded the bullet directly into the rifling from the breech using a guide shaped like a cartridge.
Pope didn't invent the false muzzle, that dates to the muzzle loader days a fellow named Alvin Clarke came up with the idea, but Pope went to great lengths to promote its use with target rifles. I've heard of bolt action rifles with false muzzle loading, but don't know who made those.




On the issue of drawings, did you read my post (a few posts back) about the acrylic, simulated barrel. I think building that and making the information available, would really help a lot of folks. Please go back and read it, and tell me you opinions. I would need help doing the math, to recalculate correct pressure ratios. I do have a lot of the parts necessary to build it though. Including the acrylic tubing.

That would be beyond me these days, I barely have the attention span to follow a thread, and math never was my long suit.

Using plastics you'd never convince the doubters that the results would hold true with metal.

An easier method, for those with the skills would be animated giffs. Differences in pressure and engraving could be color coded for easier comprehension.

I do vaguely remember finding a site that had flouroscopic photos of a cartridge firing in a chamber.
If I could find that site again I might find access to other such flouroscope photos which might be useful. Definition of flouroscopes through metal is poor so differences in a few thousandths of an inch of bullet diameter might not be visible.

[StarMetal]

Not exactly, Pope made a great many rifles, some in the Schutzen style more or less, but the schutzen is a European target rifle, predating the cartridge era. Some schutzens use the false muzzle along with a blank, but some loaded the bullet directly into the rifling from the breech using a guide shaped like a cartridge.
Pope didn't invent the false muzzle, that dates to the muzzle loader days a fellow named Alvin Clarke came up with the idea, but Pope went to great lengths to promote its use with target rifles. I've heard of bolt action rifles with false muzzle loading, but don't know who made those.



That would be beyond me these days, I barely have the attention span to follow a thread, and math never was my long suit.

Using plastics you'd never convince the doubters that the results would hold true with metal.

An easier method, for those with the skills would be animated giffs. Differences in pressure and engraving could be color coded for easier comprehension.

I do vaguely remember finding a site that had flouroscopic photos of a cartridge firing in a chamber.
If I could find that site again I might find access to other such flouroscope photos which might be useful. Definition of flouroscopes through metal is poor so differences in a few thousandths of an inch of bullet diameter might not be visible.

This isn't the site, but interesting:

http://books.google.com/books?id=fQEAAAAAMBAJ&pg=PA1&lpg=PA1&dq=x+ray+of+bullet+in+the+barrel&source=bl&ots=JSSGRpBDSk&sig=buTzbOrbNDOiQgUc2tkQosxfV6o&hl=en&ei=gMK2S4LzJoWw9gT-99zqAw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCAQ6AEwBw#v=onepage&q=x%20ray%20of%20bullet%20in%20the%20barrel&f=false

[Multigunner]

This isn't the site, but interesting:

http://books.google.com/books?id=fQEAAAAAMBAJ&pg=PA1&lpg=PA1&dq=x+ray+of+bullet+in+the+barrel&source=bl&ots=JSSGRpBDSk&sig=buTzbOrbNDOiQgUc2tkQosxfV6o&hl=en&ei=gMK2S4LzJoWw9gT-99zqAw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCAQ6AEwBw#v=onepage&q=x%20ray%20of%20bullet%20in%20the%20barrel&f=false

ool pics. As you can see definition is poor. It may be an optical illusion but it looks like the flat base bullet has swelled more in the body than at the base, which would indicate that inertia is responsible for its obturation rather than direct gas pressure.

As discussed earlier boat tail bullets can't expand at the base, and they usually allow some blowby no matter how tight to the bore. This is why square cut grooves are falling out of favor, with radiused and angled wall grooves being introduced for sniper rifles and long range match rifles.

[AriM]

I have long thought this. Umm... this does relate to obturating lead alloy somehow, right?[smilie=1: :mrgreen:

So, should we not find a more suitable word for the expanding boolit. Do we all understand 'upset' to mean lateral plastic deformation of the boolit?

Just a thought on why a boolit should 'uset' laterally without crushing the lube grooves - compressing or stretching a body does not result in tensile or compressive deformation, rather it results in shear at an angle, something like 45° (in a ductile material, anyway). This is why the shear strangth and the compressive strengths are not the same. This means that an 'upsetting' boolit would deform laterally a lot more than axially. (I've only just realized this!):idea:



of course it's related!!!! everything is relative!!! :mrgreen:

actually the term "upset" has a few definitions. look it up in the wikipedia definition of obturation, and also on it's own. another word that isn't totally clear (in relation to firearms). what we really need is a firearms dictionary.

also think of this. gravity will constantly want to pull the nose of the boolit down. so even under great velocity and pressure, the boolit will always have a slight cant to it. since minute pressure variations exists all around the boolit, during all points of ballistic trajectory, the flight path is always bowed. even in the bore. I believe this also applies to cartridges that headspace on the case mouth. this is a long standing theory of mine. this is very well documented in Hornady's newest reloading manual. I believe that the "upset" and slip of material (shearing) further adds to this as the boolit travels down the bore. This can be plainly seen in starmetals picture. I would believe that this continues (to some extent) once external ballistic flight is reached. IMO the areas of high and low pressure gas/air/etc. also deform the boolit in flight. I think this can be proven with a gross overcharge. It would explain why an overcharge on a really soft boolit would cause it to explode. Also the material lost would not reduce inertia. So all the energy of the initial charge is stored in a progressively smaller mass. My theory is that there is a threshold, where inertia and energy stored on a decreasing mass, would cause catastrophic failure. This wouldn't happen in the bore, because the harder material contains the energy and keeps the mass bonded. As soon as that mass sees cooling in the air and has the ability to deform, without limits of the bore, BLAMMO!!!!

At least it makes sens in my mind.

[303Guy]

Also the material lost would not reduce inertia. So all the energy of the initial charge is stored in a progressively smaller mass.Consider this; in order for material to be removed from the boolit in flight or the boolit to be deformed in flight, the air through which it passes must exert a force against the boolit and this will be in the form of the boolits inertia. If a force is being exerted on the boolit, the boolits inertia must change. the energy consumed in defrming the boolit remains as heat in the particles removed, the remaining boolit and the air molecules that did the 'work'. In short, the boolit slows down but also heats up, becoming softer and as the deformation progresses, so the magnitude of the deforming force will increase. Also consider that the energy of a small but high velocity boolit is very high relative to its mass. So the delayed Kaboom effect is what one should expect to see, right? And to a lesser degree, a boolit hole in paper with little lead speckles around it.

[StarMetal]

Isn't it that gravity equally pulls down on the whole bullet, not just the nose? It's the spin that tries to keep the bullet nose forward. Isn't it too much spin and not enough spin will make a bullet fly nose up or nose down?