Regardless of your opinions on obturation, have you investigated it for yourself?

[Russel Nash]

Have you actually done some sort of experimentation to prove one way or the other that obturation of typical modern day cast boolits happens or not?

[Doc Highwall]

Dr Franklin W. Mann did all the tests in his book, The Bullets Flight from Powder to Target. Excellent book!

[Russel Nash]

That's not the question.

That book was written in 1909! :-? :confused:

http://www.amazon.com/Bullets-Flight-Powder-Target-Ballistics/dp/1120732107/ref=sr_1_1?ie=UTF8&s=books&qid=1262381222&sr=8-1

[Bass Ackward]

Yes And it's very easy to do. In fact, it is practically a necessity if you begin to work with an unknown mix. More so if you DON'T have a hardness tester.

You start with a bullet using a minimum charge with a low pressure cartridge. You shoot over a chrono and watch your velocity. You increase loads .5 grains at a time and the velocity increase will be proportional to each .5 grain increase. Then, all of a sudden, the next .5 grain will produce a much larger increase that represents seal of the gas and more complete combustion.

The gun will be cleaner because the powder burned better as it actually came up to pressure and burned properly.

In actuality, it isn't just how hard your bullet is, but how far a certain bullet design has to bump up to seal and how fast the pressure is applied. (powder speed) If you are shooting .429 bullets in .433 throat, you will need much more pressure, sooner to obdurate a certain hardness than if you size so that you only need .001 to seal. So you can also see that case neck tension and bullet design also plays a part here to what you will observe when you run your own tests.

Obviously, you do finally have to produce enough pressure to seal or you won't observe what I just described. Shooting WDWW in a 38 Special sized to bore should not produce what I described unless you are running MUCH more pressure than you should be with that cartridge. So you have to keep this in perspective.

[Edubya]

I've witnessed the results of many forces, including many solids, causing obturation or deforming of the solids. I've also witnessed the results of gravitation. I accept the theorists' explanation as being truth.

Check this one out: "Newton's laws of motion are three physical laws that form the basis for classical mechanics. They are:[note 1]

1. In the absence of force, a body either is at rest or moves in a straight line with constant speed.
2. A body experiencing a force F experiences an acceleration a related to F by F = ma, where m is the mass of the body. Alternatively, force is equal to the time derivative of momentum.
3. Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction.

These laws describe the relationship between the forces acting on a body and the motion of that body. They were first compiled by Sir Isaac Newton in his work Philosophiæ Naturalis Principia Mathematica, first published on July 5, 1687.[1] Newton used them to explain and investigate the motion of many physical objects and systems.[2] For example, in the third volume of the text, Newton showed that these laws of motion, combined with his law of universal gravitation, explained Kepler's laws of planetary motion."

http://en.wikipedia.org/wiki/Newton's_laws_of_motion

Lead is a solid but is mailable, and with 15,000 psi behind it and an equal amount of force in front of it, I am thoroughly convinced that it will expand to its limit.
EW

[runfiverun]

bass explained why i gotta use 15 grs of 2400 in my 44-40.
as you know from the other thread i use 428 sized boolits in the 430 sized bbl.
there a reason i keep on talking about soft alloys.
you still have to be careful about stripping the lead on the lands but maybe thats why i have 15 different powders on the shelf.

[Russel Nash]

Bass Ackwards wrote:


Then, all of a sudden, the next .5 grain will produce a much larger increase that represents seal of the gas and more complete combustion.



I do NOT know for certain that what you are measuring...or what you think you are measuring is what you think you are actually measuring.

You are inferring something that might be caused by something else.

Back in my experimental research and design days, we called it validity or valid.

Validity coupled with reliability were the two gold standards of experimental research and data gathering.

I will give you an example...GPA...yeah, that's right, grade point average.

Is GPA a measure of intelligence?

Or is it a measure of motivation?

Is it a measure of both motivation and intelligence?

Or is there some third variable in the mix....like a person's ability to cheat or plagarize to get good grades?

[Tazman1602]

That's not the question.

That book was written in 1909! :-? :confused:



........and it's still the definative work on the subject I believe......

There's a good explanation of this from some tests Richard Lee did shooting into a swimming pool with his son John in the new manual from Lee. Simple explanation but elegant. He shot two rounds into the pool, one at extremely low velocity and one at regular velocity. The low velocity bullet showed no rifling present and signs of gas cutting. The second one showed rifling engraved properly and no sign of gas cutting. He claims chamber pressure is more important that bullet hardness. Page 107 of his manual. Very interesting reading and I"m just beginning to comprehend it. I've always been taught "harder is better" but it's appearing to me more and more that ain't exactly so until you reach a certain chamber pressure. I got a lot more work to do on this and an NO expert.

Bass did a really good explantion of the same thing. In essence -- in a rifle anyway, you can see the change in velocity Bass mentioned on the Chrono but you can also tell if you don't have enough of a charge (chamber pressure) as you'll get barrel leading/gas cutting because the bullet can't seal. Now this statement makes a LOT of assumptions, right size bullet, bore slugged, known variables accounted for etc.

..............it's also going to be next spring before the snowbanks I've fired into melt so I can recover the bullets I've fired, I don't have a pool.............<GRIN>

OH! And F.W. Mann died broken hearted because his work was shunned by most US authorities until about 50 years after he died...

Art

[Russel Nash]

What I am curious about is if anyone here shot let's say a .452 boolit through some .45 caliber gun...then they recovered the boolit in some non-destructive medium (water for example), is the boolit still swelled up and actually measures 0.4525 or 0.453 ??

A direct measure of obturation versus an inference.

[Edubya]

I'm sure that you are not trying to be a contrariian, but maybe you are looking for someone else to do your proofing for you. Look, many have voted and many have spoken their readings and understanding and you have not budged. Maybe it's time for you to tell us what you have found with your experiments, big guy.
EW

[Russel Nash]

If I had done my own experiments, I would have come right out and said I did. I wouldn't be here posting a poll, asking people for their opinions.

Who is being contrarian now?

slight thread drift ahead... In the past few weeks, I have been involved in my fair share of internet pee'ing contests. I will list the subjects for you:

1. smoke from cast boolits is caused by the lube

2. strictly fancy expensive jacketed hollow points should be used for self-defense loads

3. .45 ACP rounds headspace off the case mouth in 1911's

4. if you shoot a Beretta, the slide will eventually snap in two and hit you in the mouth

anywhooo.... I am thinking that this obturation thing is just another myth spread even more rapidly now because of the internet.

(another myth for you is that you can't shoot lead boolits out of a Glock :roll: )

[Doc Highwall]

Tazman1602, ........and it's still the definitive work on the subject I believe......
I agree, and I believe this was tried to be disproved in the 60's and all they proved in the end was that he was right in his findings.

[Bass Ackward]

Russ,

How do you know that your brass expands to seal? You get dirt in your chambers don't you? But yet it sticks if you have too much pressure.

Plain and simple. If you put enough pressure behind something, it will expand until it reaches something stronger to constrain it.

Then how is lead any different? If the pressure behind it exceeds the strength it will expand. If it over obdurates that it over comes the lubrication of the lube, it leads.

But just because it does, doesn't always mean that it will. Conditions.

[Russel Nash]

Edubya wrote:


Lead is a solid but is mailable, and with 15,000 psi behind it and an equal amount of force in front of it, I am thoroughly convinced that it will expand to its limit.


Huh?

What did you just say?

You almost make it sound like there is a 15,000 psi force pushing on the butt end of the boolit and then there is an equal amount of force being applied in the opposite direction on the nose of the boolit.

If the boolit expands outward...it obturates...then it also has to get shorter.

From the 3rd law of thermodynamics....matter can neither be created nor destroyed....

[Edubya]

One of us is gonna get an "F" in physics.

"F and −F are equal in magnitude and opposite in direction."
If a Force is applied to a body there will be an equal and opposite Force
"3. Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction."

No p-ing here, if this doesn't help find it on your own. I dunno nothing.
EW

[ETG]

Any nondestructive media will exert forces on the nose of the bullet. How do you attribute the effects of the powder charge verses the media to stop the bullet to bullet shortning. The higher the velocitys the greater the effects. The most reliable test I have read in this thread would be the presence and extent of rifling marks on bullets fired into pools. The effects of the media would not influence the rifling marks where it will the overall bullet length.

Just an FYI - GPAs are not a valid indicator of anything nor are intrim assessments. That is why educational research and evaluation use norm referenced, criteria referenced, or other validated measures.

[Russel Nash]

^^^ Not to mention that there is big ...BIG...HUGE money in having kids take the SAT's and ACT's in order to just be able to apply to college.

Just sayin..... :-P

[Russel Nash]

Edubya wrote:


One of us is gonna get an "F" in physics.

"F and −F are equal in magnitude and opposite in direction."
If a Force is applied to a body there will be an equal and opposite Force
"3. Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction."

No p-ing here, if this doesn't help find it on your own. I dunno nothing.
EW

Okay... I think I know what you're saying now... that the F applied in the opposite direction is what gets applied to the breechface and ultimately ends up being what we call recoil.

Or at least that is what I think you are saying.

[Deliverator]

It exerts that force on the first body, that first body being the expanding gases in the chamber, NOT the air in front of the bullet. According to newton's third law, the gases are exerting a force on the base of the bullet, and the base of the bullet is pushing those gases back just as hard.

[ETG]

One of us is gonna get an "F" in physics.

"F and −F are equal in magnitude and opposite in direction."
If a Force is applied to a body there will be an equal and opposite Force
"3. Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction."

No p-ing here, if this doesn't help find it on your own. I dunno nothing.
EW

Nash had a valid point in that he said 15,000 psi would not be on the nose of the bullet - 15,000 would be applied to the base of the bullet. If you had 15,000 psi on the nose of the bullet and 15,000psi in the chamber the bullet would come out looking like a cylinder. The compressive forces on the bullet will decrease as you approach the nose of the bullet - the effective mass (at that point) decreases as you approach the tip. The base has the whole mass of the bullet in front of it while there is little relative mass at the tip. Think of a bullet retrieved from a target or animal - the tip of the bullet is deformed much more than the base even though the base was traveling at the same speed. In this case the point of the bullet has the entire bullet mass behind it where the base doesn't.

[Russel Nash]

Bass ackwards wrote:


How do you know that your brass expands to seal? You get dirt in your chambers don't you? But yet it sticks if you have too much pressure.


The chamber area of say a 1911 can get dirty for a number of reasons, just one of which being that the brass didn't expand up enough to seal the chamber.

I remember back in the day when I used to reload with Unique that I would have unburnt powder on my forearms and my shirt.

Here's a good video on the subject:

http://www.youtube.com/watch?v=l5PHkv3f-9U

at about the 54 second mark in the video, you can see all sorts of stuff flying out of the chamber.

[yondering]

I believe the real debate is not whether obturation happens, but whether it is necessary, if your boolit fits the throat and bore properly. There are 2 sides to this argument, the way I see it:
1 - Use soft lead boolits, hardness being determined by the pressure of your load, so that the boolits will obturate to fit the internal dimensions of the gun.
2 - Use boolits that are sized to fit the bore and/or throats, or slightly larger. No obturation is needed because the boolits are already big enough. Boolits can be hard or soft, whatever produces best accuracy.

Looking for rifling marks is just plain silly, in my opinion. If the boolit is too small to show rifling marks, you are doing it wrong. Size the boolit large enough to fit the gun!

[357maximum]

Any open minded person that has to clear alot of snow from their driveway and also shoots into the resulting pile of snow has done a very simple experiment if they own a MIC.........anyone that has measured before and after is going to tell you the same thing about the results of this "experiment".

[hazwoper]

There is a similar discussion regarding the LEE 405HB elsewhere here regarding obduration. I have on my lap a copy of Franklin Mann's book (4th printing, 1948). If one is interested in this and can get a copy of this book, I suggest reading from P.60, and note Fig. 32, Plate 6, Fig 33, 34, 35, Plate 8, Fig. 36 and 37. I believe F. Manns work was well executed, and exceptional for his day.

[AriM]

I hate to add fuel, but some proposals, in replies to the original topic....utterly defy physics, science, and common sense....I have no doubt, however, that a specific velocity is required for certain types of projectiles to achieve optimum results....anyone who has reloaded a variety of different variables, already knows this....

Some barrels like a fast jacketed bullet, some like a powder puff lead bullet....and then there are almost infinite variables which govern the bullet itself....

you might have a SWC that shoots like ass from a revolver with a light load.....step up the powder to a critical tolerance and it drives tacks....anyone with actual reloading experience knows this....

there are entirely too many variables for a lone shooter to come to a definitive answer....we can only test one variable at a time, and often our measurement methods are too crude to equal anything more than an educated guess.....

it's totally un-scientific and fool hearted to say that because a + b = c that c always equals a + b

MHO

[ETG]

Looking for rifling marks is just plain silly, in my opinion. If the boolit is too small to show rifling marks, you are doing it wrong. Size the boolit large enough to fit the gun!


You obviously missed the point. Two bullets of the same size fired form the same gun. One low pressure and one normal pressure. If there isn't expansion then what do you think caused the difference in the rifling marks?

[powderburnerr]

well my input is .I shoot a 440 dia bullet in a 45 cal rifle when it is loaded it slides down the barrel under its own weight , when the bullet is recovered it is between 15 and 30 tho shortwe and is engraved with rifling marks , this is not a muleloading rifle , it is a ctg, rifle... it is my standard load for this rifle ,,,,,,,,,,,,,/dean

[Marlin Hunter]

4. if you shoot a Beretta, the slide will eventually snap in two and hit you in the mouth






:bigsmyl2::bigsmyl2::bigsmyl2::bigsmyl2::bigsmyl2: :bigsmyl2::bigsmyl2:

[Marlin Hunter]

Here's a good video on the subject:

http://www.youtube.com/watch?v=l5PHkv3f-9U

at about the 54 second mark in the video, you can see all sorts of stuff flying out of the chamber.


I wish I could see youtube :sad:

A couple weeks ago I shot some 5744 powder. It looked like someone poured a 5 pound bag of pepper all over my bench.

[stubshaft]

I have duplicated Veral Smiths tests in a 30 carbine T/C barrel. An undersize slug is loaded ahead of powder charges that increase. As the slug is fired (and recoverd in water to lilit any distortion) it will show an increase in the expanded base portion and the rifling marks will be easily discernible. The portion that is engraved by the rifling increases in proportion to the increase of the powder charge.

[Bullshop Junior]

That's not the question.

That book was written in 1909! :-? :confused:

http://www.amazon.com/Bullets-Flight-Powder-Target-Ballistics/dp/1120732107/ref=sr_1_1?ie=UTF8&s=books&qid=1262381222&sr=8-1
What does that matter?

[geargnasher]

I only develop opinions on something if I have investigated it myself.

I have, in fact and on many occasions, seen direct evidence that a malleable chunk of lead kicked in the pants mushes to fit whatever is strong enough to contain it.

Check out the sticky on the 300 yard milk jug in castboolits, you may have a hard time believing it to happen, but one thing being discussed is tests proving that rifle boolits deform enough under firing to actually change their BALLISTIC COEFFICIENT. That is significant.

Gear

[Bullshop Junior]

I have mistakenly shot 270 boolits (.276") out of my 7mm/08 rem (.284" groove / .277" bore) They actually shot quite well, and shot point on at 100 yards. No I did not recover the boolit, but it would seem to me that if the boolit was not obturating it could not shoot point on at 100 yards, because it is smaller then bore diameter starting out.

[John Boy]

Cast Length - 1.361
Spent Length - 1.284
http://i222.photobucket.com/albums/dd220/Meadowmucker/Targets/MKIIISpentvCast.jpg

And if you really want to see more pictures, put a post on Shiloh Rifle Forum. Several of the top match BPCR shooters have performed extensive testing on GG and PP bullets that were shot into snow banks - showing the effects of obturation on lead cast bullets

[John Boy]

...
to prove one way or the other that obturation of typical modern day cast boolits happens or not?
Russel, I find your statement hilarious, the part about ... modern day cast bullets. Obviously you are not knowledgeable that bullets designed and shot in the 1800's are the same bullets cast and shot in 'modern day'

I cast and shoot several of these 1800's oldies ... the 375166 (the standard 38 caliber 38-55), 454190 ( the standard 45 Colt) and 457193 (the standard 45 caliber bullet designed for the 1876 Winchester). And I just acquired another rare oldie mold, 1890's vintage bullet, the Ideal 375272
http://i222.photobucket.com/albums/dd220/Meadowmucker/Molds/Ideal375272DocHudson-1.jpg

You need education! Buy a copy of an Ideal bullet mold handbook and then compare the bullets in it to the Lyman bullet molds carried currently in Lyman's current production inventory. If you are too cheap to buy the Ideal Handbook, use this chart to compare old Ideal bullets to Lyman's current bullets ...
http://www.castpics.net/IdealandLymanMolds.pdf

And BTW, Pb has not changed in centuries!

[JD Yellowhammer]

Must be a slow morning for those of us participating in this discussion/argument/exercise in futility or whatever this is....

We don't really need to have bullets to figure out whether obturation is for real. We can apply common sense, real-life experience, and some deductive reasoning to get there.

Start with Newton's first law. Part of that law states that an object that is not in motion (velocity = zero), will remain at rest until some force causes it to move.
Next, let's think about what happens when that force causes the object to move:

You're stopped at a red light in your '57 Chevy with the supercharged 350 small block. Light goes green and you tromp the pedal. Following Newton's law, your body is at zero velocity and wants to stay there. But the force of that motor wants to accelerate your body. So your body gets pushed back into the seat and your head, which is unsupported (because who would trash up a classic car with headrests?) snaps back.

Let's consider our experience with lead. It's a soft metal. Hit it with a hammer and it deforms. As mentioned in earlier posts here and the other thread, if you could hit the lead with a bat, hard and fast enough, the lead would deform. This is because the lead does not want to move (Sir Newton). It wants to stay at rest, forever. (Once it starts moving it wants to stay that way forever, but gravity, friction, etc., ruin the plan).

Okay, so there's a lead bullet in a case. The lead doesn't want to go anywhere. Suddenly, a spark ignites a column of gunpowder. The burning causes gasses to expand. The gas expands in the direction of least resistance, which happens to be the mouth of the case, which only has a lodged bullet to stop the expansion. It's no contest, the bullet loses.

But still, the bullet, like your head and body in the Chevy, doesn't want to move, it wants to stay at rest. But it can't.

And since the force pushing the bullet starts at the back, that part of the bullet moves first. It can't push the rest of the lead out of the way fast enough. And since it's a soft metal, it expands! Into the grooves! Obturation! Then the force catches up to the front of the bullet and it goes spinning out of the barrel, hopefully into the 10.

qualifier: don't nitpick words or change the factors. We're talking soft lead that isn't too big for the barrel, i.e. it has room for expansion withing the tube.

[Russel Nash]

@ John Boy... Thanks, man! That is exactly what I was looking for:

:drinks:

http://i222.photobucket.com/albums/dd220/Meadowmucker/Targets/MKIIISpentvCast.jpg

One dumb question for ya, though, where did that first ridge go?

When you look at the boolit on the right (which I assume to be new) there is a ridge on it right below the ogive?

Then on the dirty, fired, corroded/tarnished boolit on the left, there is no ridge.

[Russel Nash]

@ John Boy.... what I mean by modern day cast boolits was meant to just specifically exclude the Minie balls of softer lead from about a 150 years ago.

[montana_charlie]

What I am curious about is if anyone here shot let's say a .452 boolit through some .45 caliber gun...then they recovered the boolit in some non-destructive medium (water for example), is the boolit still swelled up and actually measures 0.4525 or 0.453 ??

A direct measure of obturation versus an inference.
I have some comparative pictures if you need them.

I fired a paper patched bullet into a snowbank, so it was very easy to read.

The bullet, itself, was .452", and the shank was patched to .457", a diameter that is .003" below groove diameter.

When fired the body of the bullet, combined with the patch, filled the bore and both materials were engraved by the rifling...BUT, to answer your specific question...

The nose of the bullet ahead of the ogive was less than bore diameter.
When fired, the nose 'bumped up' to bore diameter...as evidenced by the engraving of the lead ahead of the paper patch.

The amount of force applied, coupled with the hardness of the alloy, caused that engraving to extend .100" ahead of the patch. Less pressure would have caused less 'obturation'...and a shorter length of engraving... as would a harder alloy.

On the next reload, the patch paper was cut to a different dimension, which caused it to cover more of the bullet's ogive. When fired, the engraving begins at about the same point on the bullet, but (on that one) there was paper between the lead and steel.

The 'under bore diameter' nose did bump up to (slightly more than) bore diameter during firing.
The measurements and visual markings, of the recovered bullets, confirm that the dimensional change was not caused by impact with the snow.

CM

[ANeat]

One thing I found out like many others, one indication of a too hard bullet not obturating soon enough is a bit of leading at the chamber end of the barrel that goes away as the pressure builds.

Going to a softer bullet will generally cause the leading to go away as the bullet obturates sooner, sealing the bore

[yondering]

You obviously missed the point. Two bullets of the same size fired form the same gun. One low pressure and one normal pressure. If there isn't expansion then what do you think caused the difference in the rifling marks?

I didn't miss the point. Of course obturation can/does happen, we all know that. You may as well prove that the sky is blue. We're talking about lead, not stone.

My point was that while bullet obturation can happen, it isn't necessary in most smokeless cartridge applications. If the boolit is sized at or larger than throat diameter, obturation is un-necessary, and chamber pressure and boolit hardness don't have to be matched so precisely.

There are exceptions of course, for example a revolver with throats so oversized that a loaded round with a boolit sized at throat diameter won't chamber. In this case, the shooter is limited to relying on boolit obturation. Note that this is a handicap, not an advantage.

[lwknight]

As others have pointed out, a boolit cannot obturate itself. It obturates the barrel as it is expanded under great pressure and that word can be technically correct when use as a "for short" meaning, that it obturates the barrel.
Its just not grammatically correct to say that the boolit obturates without adding " the barrel"

I just threw that in because some folks get on a rant about he useage of the word obturate and obturation. Big deal, so what. We all know what we mean. huh? LOL

[felix]

Correct! Obturate comes from Latin "to close". The word does NOT mean "to expand". When you get down to it, there is no English word "obturation", but there is in Latin. ... felix

[montana_charlie]

The word means to close (an opening) or to obstruct passage (through an opening).
A 'bumped up' bullet does both of those things when pressure has caused it to expand.

That is to say a bullet DOES both of those things.
Yes, Matilda, the bullet odturates the bore...so bullets DO obturate.

They also 'swell up'.

Russel Nash doesn't want bullet obturation to be true (for some reason) so we are left with wringing the last bit of goodness out of the terminology.
The whole endeavor is useless. We all know what a bullet does...and Russel can believe whatever he wants.

CM

[MT Gianni]

Dr Mann quoted a rifle blow up with a mistaken powder overloaded. The gun was an '06 and the cartridge a 270. If the bullet, a jacketed lead core, did not expand the pressure would not have burst the receiver.

[Wayne Smith]

@ John Boy.... what I mean by modern day cast boolits was meant to just specifically exclude the Minie balls of softer lead from about a 150 years ago.

.38 Special swaged bullets are pure (soft) lead. Modern bullets. You can cast pure lead, 1-30 tin-lead, 1-20 tin-lead, 1-16 tin lead and I know 'cause I have. These last two are the same formulas used by Remington and Sharps. I cast heeled boolits for my .41 Colt. The inside the case boolit for this caliber (.40) is a .386 diameter boolit, hollow based but depending on obturation to function without tumbling.

I don't understand your quibble about "modern cast boolits", the formulas used now are very similar to the ones from the turn of the century. They used tin/lead/antimony mixes. Dr. Mann's work is wholly valid for cast boolits, perhaps questionable for jacketed. They have changed hugely since he began working with them. He took a barrel and gradually shortened it, showing photographically what happened to the bullet. I find it amazing that, in a very short barrel, the bullet actually expands greatly larger than the bore upon exiting the bore. If that doesn't prove lead expansion under pressure, and the pressures found in gun barrels, I don't know what will.

[John Boy]

One dumb question for ya, though, where did that first ridge go?
You meant to say, Where did the driving band go?
Could be do to:
* chamber pressure
* obturation
* velocity
It was there though when I chambered the round!

[Old Caster]

Russell. If a hollow base wadcutter is fired with too much velocity in a revolver the back of the base can come off because gas pressure wanting to escape out the front of the cylinder will press through the front part of the hollow and cut off the back. This is obvious after it happens because the back part of the bullet stays in the cylinder. If you inertia pull a factory HB wadcutter from a .38 it will measure about .355 to .356. I think this is because the lead is so soft that the case crushes it when installed. Nonetheless they shoot very accurately because they will swell to barrel size from the pressure, swelling even to breaking in two with enough pressure and a place to swell to. If there is no opening to break out of like the space between the front of a revolver and the barrel it will only swell to the size of the barrel, that is, if if the acceleration is fast enough and the material is soft enough. When it gets too hard with not enough acceleration it stays the same size. In other words, if a 30 caliber lead bullet were put in the back of a .38 caliber barrel and pushed through with a rod with your hand it would come out the same size. If the same were done with a rod going fast enough it would flatten the lead out to bore size. If the material were marshmellow it wouldn't take near as fast of a push. We know the wadcutters go up to bore size from the small size they start out at or it wouldn't shoot accurately. This also happened with the old pure lead Star that shot so accurately out of all .45's when only measuring .450 to .451.

[swheeler]

I've experienced it shooting 6.5 Swede with undersized cast bullets, .266", using a light charge of ball powder(wc846) The acww loads chronied 1465 fps-es37- for 5, the h2o dropped 1388-es69- for 3- I quit shooting. The ac left the necks black and dirty, the water dropped blew gas back in my face and the cases were black all the way to the head, everthing was the same with both loads except bullet hardness. The softer bullets obturated to better seal the barrel than the harder one did.That is also about the time found this forum, decided it was time to look for help.

[Jayhem]

I KNOW that obturation happens by evidence I have seen from years of shooting muzzleloading rifles with soft lead cast maxi-type bullets.

In particular, my .45 cal hawken rifle. I cast soft lead, 255 gr TC hollow point maxi-type bullets for it. This boolit has 4 rings that must contact the rifling. When the bullet is loaded ONLY the top ring makes contact with the rifling lands and must be "engraved" into the lands by force with the ball starter in order to load the projectile. So the first 3 rings of the boolit only ride on top of the lands when loaded.

However, I have recovered quite a few of my fired boolits from paper, clay, water backstops and all of them show deep rifling engraving on ALL 4 boolits rings and each ring measures exactly what my bore slugs at.

If this isn't proof of obturation...what is?

[sheepdog]

That's not the question.
That book was written in 1909! :-? :confused:
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Did elemental properties of lead changed since them? Nope.

Did alloy properties of brass change since them? Nope.

Primers or power changed very much since then? Nope.

I'd say its fairly well the same game as when that book was written, do you have reason to doubt that logic?

[AriM]

Did elemental properties of lead changed since them? Nope.

Did alloy properties of brass change since them? Nope.

Primers or power changed very much since then? Nope.

I'd say its fairly well the same game as when that book was written, do you have reason to doubt that logic?

I am not sure his point was that anything may have changed, but more as to the modern analysis of such topics....our perception of data changes, as science progresses....there are process which are taken for granted, with poor testing methodology and equipment....as the method is refined and the gear is refined, we often refine our original conclusions....look at engineering in general...the wright brothers understood enough about flight to get a plane up in the air....but through better understanding and quantification, we now have supersonic, high altitude aircraft....the properties that govern flight have not changed, nor has the medium....but the process is greater understood

to say that we know EVERYTHING about ANY subject, is foolish indeed....

[randyrat]

Is that one bullet shorter because of force from the rear or from hitting the dirt?

[Russel Nash]

^^^ I was under the impression it was shot into a snow drift bank and then later recovered.

Now that the guys here have set me straight about how soft a lead pro-jo they are shooting, I am ASSuming that the scrunchiness of the darkened boolit is from the inertia...the nose end gets pushed back into the rear end under all those acceleration forces and that makes the boolit shorter as the middle squishes out.

Much like squishing a marshmallow between your thumb and index finger.

The caption on that pic says "as cast"....so I have no idea what a sized boolit looks like...unless of course they are shooting them as cast.

Anywhooo...

AriM was spot on about what I was getting at. Thanks Ari. :grin:

[johnlaw484]

Do I really care about all this? NO. All I care about is whether the round goes on target.

[rbuck351]

I just make my boolits larger than the hole they are going through and I'm pretty sure they obturate because they come out the front. I assume they have to get smaller to do that. No real sceintific testing. Also Minie balls that fit loose in a barrel come out with rifling on them so either the barrel shrank or the bullet expanded. Never bothered to check which. When a car is rear ended it gets shorter and fatter. I suspect that when a boolit gets rear ended fast enough and hard enough, it reacts the same way. Haven't tested that theory either. I'm curious as to why one would think that a boolit wouldn't expand if enough pressure was applied to it's base fast enough.

[RobS]

As mentioned bullet fit is ideal so a person doesn't have to worry about obturation of the bullet to seal the bore. With that said I work to always have a bullet .001 to .002 over groove diameter so I can shoot just about any bullet hardess I desire without leading. Now bullet hardness is another topic which I won't go into on this thread.

Obturation does happen and proof is simple with this example.

I cast up some wheel weight bullets where the mold dropped bullets that would end up .001 under groove diameter for the intended revolver. No, this is not optimal, but I wanted to try the design. Anyway, as soon as the bullets cooled I lubed, reloaded, and then shot them. Most people understand that an air cooled WW bullet will age harden and become harder within the next few days. The bullets that were freshly cast were to no doubt softer with a BHN readings of 6.

No leading from the bullets shot a few hours after being cast. A week later the same batch of bullets then had a BHN of 11-12 and when loaded with the same powder charge resulted in....:(the test results are in:(....leading in the barrel due to the inability of the bullet to obturate and seal the barrel. In turn, the same bullets at 11-12 BHN with a larger powder charge increased the pressure and leading once again deminished as the bullet base would expand enough to seal off the gas blow by.

Obturation.............it does exhist..........but bullet fit has a lot more to do with accuracy.

[jhalcott]

I know what I have done to convince MYself that obturation occurs with LEAD bullets. I leave it up to YOU Mr Nash to prove it does/not happen with Jwords! As has been repeated here OFTEN, low pressure against hi pressure loads show the differences!