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

[Marlin Junky]

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

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.