Do cast boolits generate higher pressure?

[Black Jaque Janaviac]

I've read conflicting opinions. Some have said that the reason cast boolit recipes have lower powder charges is because cast boolits generate higher pressures. I've also read that cast boolits generate lower pressures and you can generally substitute a cast boolit with a jacketed boolit recipe.

[felix]

Both statements are correct. If the boolit obturates too snugly, then the pressure goes higher than normal. ... felix

[ddeaton]

Good question. I have always wondered about this myself. I have just always loaded on the safe side. Now that I can control the size and hardness of my boolits I am worried. Lets say I am sizing 45 acp slugs to 452, same as jacketed. Will the pressure be same as the jacketed, or does it depend, now, on the hardness of the lead? Meaning the base will expand and seal better than a copper jacket since it is softer? All this depending on the same design and weight in jacket and cast.

[SHOOTER IN EXILE]

lead has a higher friction level than copper, so common sense seems that they originate more pressure but the grease on lead bullets is also a factor that reduces friction. I really would like an answer. Myself I have been wondering about this important issue.:?:

[felix]

Straight-up lead does NOT have a higher friction level than copper against common gun steels. Quite the contrary. However, most boolits are not pure lead but contain antimony. Now, antimony is very abrasive, but when surrounded by tin on the elemental level, the friction of the boolit is brought back into something we can use continually. Actually, the best way to break in a barrel is with high antimony boolits where the tin component is quite low percentage wise with that antimony. ... felix

[Gunslinger]

I second that, since I am about to start casting for my .357, which I run at pretty high pressures with normal jacketed. I too have heard that the right boolit, in the right size with the right lube will generate less pressure than a jacketed bullet in equal weight, size and over same amount of powder....

[Marlin Junky]

I too have heard that the right boolit, in the right size with the right lube will generate less pressure than a jacketed bullet in equal weight, size and over same amount of powder....

Make sure your alloy does not obturate at the pressure your load creates and your assumption will be credible. Once the bullet's base begins to distort, more energy is required to drive the bullet forward.

MJ

[Gunslinger]

I don't quite follow. Does that mean that if the bullet is too tight in the bore, this could happen? Say if a barrel is .357 and the bullet is .358? But then again, some say that the bullet needs to be that .001 larger than the bore....?

[missionary5155]

Good morning Pressure has to be measurable. That is why it is soo important to first READ the forward part of most loading manuals to understand what pressure signs are. Smashed primers are one method. Sticky ejection another. The better I know about is actualy measuring case expansion. Ken Waters list this method for most his reveiws with particular rifles. I started some years ago and I do think it is a repeatable safe way to consider MAX loads with whatever boolit design or mix.

[44man]

This is a question that has no answer. Lead has less friction so that most of the time it takes less powder to match the velocity of a jacketed bullet. A difference in the design of 2 boolits will change everything too.
For instance I have 2 boolits that look almost the same, are the same diameter to barely fit through the throats, weigh the same and are cast from the same alloy, except one wears a gas check.
The PB will take a full grain more powder before showing a sticky case, then the gas checked boolit will.
Then I have just the reverse with 2 boolits in another caliber.
I also have some boolits where I can exceed jacketed bullet loads.
What it boils down to is you just work loads from minimum to maximum looking for accuracy just like you would with any bullet. Looking for pressure signs is just standard fare as you work loads.
If you are a load grabber trying to get the highest velocity listed, you can have a problem.
There are so few loads in manuals for cast boolits that the only way is to just use the jacketed bullet info for a starting load and go from there. In some cases you can exceed jacketed bullet loads but there are some where you can't.
You must do the work in a safe manner.

[44man]

I don't quite follow. Does that mean that if the bullet is too tight in the bore, this could happen? Say if a barrel is .357 and the bullet is .358? But then again, some say that the bullet needs to be that .001 larger than the bore....?
No, it just doesn't follow that way. The alloy you use, the powder and the velocity will have more effect then an oversize boolit. You WANT an oversize boolit.
I don't think you can tell a difference between a .357, .358 or a .359 boolit.
Just work loads with what you have.

[HeavyMetal]

We are really need to step back to the basics here!

Each gun is it own seperate world! Load for each gun, seperately, if your going to push the envelope for max loads and learn to recognize signs of pressure. Keep the ammo seperated!

This is why I am not a fan of 4 or 5 guns in the same caliber with 6 different loadings from mild to wild. Sooner or later the hot stuff will find it's way into a weak action.

Ken Waters case expansion method is probabley the best, and easiest, method for the average reloader to "guess" at pressures.

You can find this information in most of his articles in Handloader Mag.

[Marlin Junky]

I don't quite follow. Does that mean that if the bullet is too tight in the bore, this could happen? Say if a barrel is .357 and the bullet is .358? But then again, some say that the bullet needs to be that .001 larger than the bore....?

You can answer your own question by trying a little experiement, remembering that the burning powder wants to force the lead out to the side as well as down the barrel. If you have a .35 caliber barrel and a couple bullets designed to wear a gas check which are cast of clip-on WW metal, try driving one of the bullets not wearing the gas check and one wearing the gas check through the barrel with a heavy hammer and a 5/16" aluminum rod. You'll see the unchecked bullet will be driven into the sides of the barrel (in the base region) more than the checked bullet and require more force to remove from the barrel. Obturation works similar to this because of the friction between the bullet and barrel walls. Please don't forget to lube the bullets before attempting this little experiment.

MJ

[Gunslinger]

Aha... there's a lot to consider, but I like it! Thanks for the replies guys :drinks:

[Marlin Junky]

Aha... there's a lot to consider, but I like it! Thanks for the replies guys :drinks:

Yes, but friction is your biggest enemy ;-) (at least when one is trying to achieve HV accuracy in a rifle).

MJ

[Crash_Corrigan]

44MAN: I disagree with your contention about .357.....358 and .359.

When loading for my 9MM Browning I now use .358 Dia. lead RN boolits. It gets major indigestion with .356, .3565 or .357 boolits. Using the smaller dia loadings it gets really sooty and dirty, cases have black soot one one side halfway to the base, weapon gets so dirty that at about 30 rounds it jams solid.

By the second magazine I get FTF and unrelialability. With Jwords I can run through hundreds of rounds with nary a worry. If I use a .358 or .3585 LRN I get the proper oburation and the cases stay clean, the gun stays clean, the gun functions reliabily and I get good accuracy just by using the right dia boolit.

SO THE GUN CAN TELL THE DIFFERENCE!

[Black Jaque Janaviac]

OK. It sounds like my original thinking is correct: there is no rule whether cast boolits generate higher or lower pressures than jacketed. So just treat 'em like a jacketed and work up from the starting point.

Reading this thread did cause me to rethink another pressure sign. Flattened primers. I get them all the time - even with factory ammo. I guess if I get flattened primers with factory I didn't figure they would be an accurate indicator.

[44man]

44MAN: I disagree with your contention about .357.....358 and .359.

When loading for my 9MM Browning I now use .358 Dia. lead RN boolits. It gets major indigestion with .356, .3565 or .357 boolits. Using the smaller dia loadings it gets really sooty and dirty, cases have black soot one one side halfway to the base, weapon gets so dirty that at about 30 rounds it jams solid.

By the second magazine I get FTF and unrelialability. With Jwords I can run through hundreds of rounds with nary a worry. If I use a .358 or .3585 LRN I get the proper oburation and the cases stay clean, the gun stays clean, the gun functions reliabily and I get good accuracy just by using the right dia boolit.

SO THE GUN CAN TELL THE DIFFERENCE!
You just read me wrong. The .357 boolit HAS to fit to begin with, not be under size. So you need to go the other way. If the .358 shoots good, you should see little difference with .359.
The starting size must be a little over bore size.
For instance, my 45-70 Browning BPCR has a bore a little over .459. I have shot all sizes until I am now using a .464 boolit that fits the brass and boolit to the chamber instead of the rifling. Grossly over bore size but so far it shoots the best.
One of the great fellows here clued me into trying it. I never shot a match with it yet, I was kind of broke the last few years. Gas, powder and fees got too expensive.

[Marlin Junky]

OK. It sounds like my original thinking is correct: there is no rule whether cast boolits generate higher or lower pressures than jacketed. So just treat 'em like a jacketed and work up from the starting point.

No, that's not correct. If we are talking about rifles, if the load's pressure exceeds the alloy's obturation point, the load will develop more pressure than a jacketed load that doesn't obturate.

MK

[44man]

MK, true but I think we already discussed that point. Felix did a good job on that problem too.
However it can happen in a revolver too.

[405]

OK. It sounds like my original thinking is correct: there is no rule whether cast boolits generate higher or lower pressures than jacketed. So just treat 'em like a jacketed and work up from the starting point.

Reading this thread did cause me to rethink another pressure sign. Flattened primers. I get them all the time - even with factory ammo. I guess if I get flattened primers with factory I didn't figure they would be an accurate indicator.

My rule of thumb is and will continue to be: Soft alloy won't shoot very accurately at higher pressures and higher velocities. So the question about higher pressures being caused by softer alloys doesn't apply to my loading. However, I suspect that softer alloys usually leads to higher pressures (let the "yabutts" begin :mrgreen:). I shoot for accuracy in lower pressure loads (both BP and smokeless) so I use softer alloys... and avoid the guessing game entirely.

Second thing.... flattened primers may or may not mean excessive pressure. High or excessive pressure can flatten primers OR excessive headspace at normal pressure can cause flattened primers OR lube in chamber or on case can cause flattened primers. Without pressure testing equipment guessing wrong may have consequences.

[longbow]

You know what? When I first read the question, my response would have been "Of course not, lead is softer than copper jackets." But before I spoke I thought (yeah, I know a rare moment) and decided to take a look at some references ~ mainly the Lyman Cast Bullet Handbook and Lyman Reloading Handbook.

As it turns out looking at "J" bullet loads vs. cast boolit loads, the pressures vary considerably ~ same powder same bullet weight sometimes higher with "J" bullet and sometimes with cast.

Obviously bullet/boolit shape and hardness have an effect but I did expect to see lower pressure in general with cast for same projectile weight and powder charge. Not necessarily so.

I don't hardly ever use "J" bullets so haven't been paying much attention to those load recipes but do always start with a good reference for cast when I am working up a load.

405 makes a good point ~ one shouldn't guess or assume.

Longbow

[missionary5155]

You can answer your own question by trying a little experiement, remembering that the burning powder wants to force the lead out to the side as well as down the barrel. If you have a .35 caliber barrel and a couple bullets designed to wear a gas check which are cast of clip-on WW metal, try driving one of the bullets not wearing the gas check and one wearing the gas check through the barrel with a heavy hammer and a 5/16" aluminum rod. You'll see the unchecked bullet will be driven into the sides of the barrel (in the base region) more than the checked bullet and require more force to remove from the barrel. Obturation works similar to this because of the friction between the bullet and barrel walls. Please don't forget to lube the bullets before attempting this little experiment.

MJ
Good morning There is a slight difference between battering a boolit through a bore with an undersize rod and launching it with rapid gas expansion. Your 5/16 rod does not exert even pressure on the entire base of the boolet ( Groove Diameter). You will not have complete boolet base support into the grooves of the rifling. When a boolit is fired in a cartridge the expanding gas pushes against the whole boolit base exerting the same pressure around the complete circumfrence to include those small portions that are filling the grooves. The applied Gas Check has the strength to support the boolit even out to the groves even though the 5/16 rod is not the perfect fit to groove diameter.
Friction and boolit setback do exist and will raise pressure. But also so will the lead material that begings to be displaced and wrap itself around the under groove sized rod that is battering the base.

[Bret4207]

Even the hardest lead alloy is far more ductile than jacketed. Add to that the hundreds of possible other factors...whew! It boggles the mind sometimes. I believe as a general rule cast develops less pressure because most cast is shot at lower pressures than jacketed. You can't make a side by side comparison even using the same weight boolits and and bullets and loads. They just react differently. Sometimes cast may show higher pressure, other times lower. It's the old apples and oranges thing. They're both fruit, but there it ends.

[Marlin Junky]

Good morning There is a slight difference between battering a boolit through a bore with an undersize rod and launching it with rapid gas expansion. Your 5/16 rod does not exert even pressure on the entire base of the boolet ( Groove Diameter). You will not have complete boolet base support into the grooves of the rifling. When a boolit is fired in a cartridge the expanding gas pushes against the whole boolit base exerting the same pressure around the complete circumfrence to include those small portions that are filling the grooves. The applied Gas Check has the strength to support the boolit even out to the groves even though the 5/16 rod is not the perfect fit to groove diameter.
Friction and boolit setback do exist and will raise pressure. But also so will the lead material that begings to be displaced and wrap itself around the under groove sized rod that is battering the base.

There's a whole lot of difference between battering a boolit through a bore with an undersized rod and launching it with rapid gas expansion. You're taking my little illustration too literally. I was just trying to contrast the difference in energy required to move a checked and unchecked bullet forward under the same conditions. The fact is, cast bullets will obturate at the base given enough pressure; therefore, increasing friction and in turn increasing the force required to drive them forward.

MJ

[Boerrancher]

Bottom line, if you don't understand how pressure works, and understand the signs of pressure, it is best to learn them before doing to much work at the loading bench. Also understand that each gun is its own world, and what is a low pressure load in one 357 mag, might be a high pressure load in another that is the same make and model.

I am shooting an IAB Sharps rifle in a 45-70. I have to shoot well above max loads listed for the Marlins and Winchesters in order for it to shoot well. It took me a lot of nerve wracking hours to work up to my loads that shoot well, but it was worth it. I do not recommend anyone do this. I probably shouldn't have, but there is still no signs of pressure, and it shoots well.

Best wishes from the Boer Ranch,

Joe

[Hipshot]

Felix,
How can a cast bullet obturate too much? It would have to bulge the barrel to do so. I don't understand.

Hipshot

[fourarmed]

It is a simple thing to test. Load cast and jacketed bullets of the same weight with the same load and fire them in the same gun. The one with the greatest velocity gives the highest pressure.

[44man]

It is a simple thing to test. Load cast and jacketed bullets of the same weight with the same load and fire them in the same gun. The one with the greatest velocity gives the highest pressure.
Not so, pressure has nothing to do with velocity! Have you not worked loads to find as they get hotter, velocity starts to DECREASE?
As you work loads, didn't you notice that the velocity increase was not keeping pace and was going up in smaller increments?
A perfect cast boolit can go FASTER with the same load with a jacketed bullet and actually have a lot LESS pressure.
Do NOT use a chronograph to guess pressure! :coffee:

[fourarmed]

44Man, I'm sure there will be others who agree with you. We'll just have to disagree on that! Velocity comes from doing work on the bullet. Work is Pressure times change in Volume. If you think you are getting greater velocity with less pressure, you are either mismeasuring the pressure or confusing peak pressure and average pressure. There is probably some wiggle room because of differences in frictional force, but not enough to change the principle, because greater friction is also going to produce greater pressure, and vice versa.

I also believe that a chronograph is actually the BEST way for a handloader to judge pressure - by comparison with pressure-tested data from the manuals. There are just too many variables for the folklore methods to be trustworthy.

[Black Jaque Janaviac]

Work is Pressure times change in Volume.

Right, but your statement about the faster bullet yields more pressure is correct only if it takes the same amount of work to push the bullet through a bore.

I'm not convinced that copper is easier to push through a bore than lead. And I'm not entirely convinced that obturation necessarily means greater resistance compared to hardness. Having slugged a bore and played with muzzle loaders - my experience tells me softer lead pushes through easier. And copper jacketed is even harder yet.

Why do they now make all-copper bullets with grooves in them? My understanding is because solid coppers generate more resistance (and thus pressure) specifically because they don't upset as easily as lead-core bullets. So they put grooves in them to allow the displaced copper a place to go.

[Marlin Junky]

Felix,
How can a cast bullet obturate too much? It would have to bulge the barrel to do so. I don't understand.

Hipshot

As the force of obturation increases, so does pressure and friction against the barrel walls. The higher the pressure behind the bullet, the farther up the bullet shank obturation will occur and the more pressure/friction will be created between the bullet and the barrel's interior. Look at it like this: When you strike a billet of lead on its end with a hammer, it not only shortens, it also increases in diameter, greater near the end that received the blow than father away from the blow. Force vectors from the expanding gases are not just shoving the bullet down the barrel, they are also trying to expand it normal (perpendicular) to the bullet's axis... or blow it apart, even (given enough pressure). The force of obturation is always greater at the bullet base and this is why gas checks are used to help keep the base from distorting. An irregularly distorted base leaving the muzzle can only mean one thing... an imprecise shot. It's doubtful we ever experience perfectly uniform distortion.

MJ

P.S. I don't want it to sound like I believe gas checks are useful for the single function described above. There's also the scraping and all important gas-checking functions; without the latter, the lube's effectiveness is diminished.

[kooz]

I breezed through this kind of quick, so forgive me if I have misinterpreted something, but it looks like there is way to much thinking going on here. bottom line is that obturation is a GOOD thing and is the key to top accuracy and minimal leading in most handguns ( I will not add my 2 cents on cast rifle bullets as I have liitle experience with them).

[Edubya]

For every action there is an equal and opposite reaction. Pressure will find the weakest resistance, thusly creating momentum.
A hand grenade will demonstrate how the pressures work, so will a piston motor. A motor cylinder will lose power/pressure if the rings are bad and blow-by will cause destruction of the lubrication. Pistons do not obturate but the piston rings do. Hard cast bullets at lower velocities don't either. The blow-by in a bullet is much hotter than the ignition behind the bullet due to the venturi. This extreme heat will melt barrels, much less lead or copper.

[Larry Gibson]

Well, I do measure pressures. While I've not done a direct comparison so far of jacketed vs cast bullets in my tests so far the cast bullets seem to generate less pressure for any given load. That is not a definitive answer by any means as it is just an observation thus far. A direct test would have to be done to answer the question. I do have some hard cast (Lazer Cast) 240 gr .44 bullets. I might size them to equal some .240 gr Speer .44s that I have and load both over 22 gr 2400 and see what happens. Hell, with the weather I haven't got to the Blue Dot pressure test yet. You guys come up with too many interesting "testing" ideas!

Larry Gibson