Lead bullet pressures are greater than jacket bullet pressures of the same weight

[swheeler]

I've learned patience is a virtue! Hey I've waited nearly 7 months for the empirical data, what's a few more months. It's all good, I have no doubt Larry will get around to it someday , carry on.

Maybe someday in the next few years?

[303Guy]

I pulled up this old thread while I was looking for jacketed loads using traditional cast boolit powders in rifles. So the issue of cast boolit pressure being higher or not than the same weight jacketed has still not been fully resolved or has it?

[Mal Paso]

Larry Gibson was on it and I think we got a partial result a couple months ago. Don't have a link.


If I remember correctly there was no consistent result and you could not depend on one being lower pressure than the other.

[JonB_in_Glencoe]

It's resolved as far as I'm concerned.
It is, unless it's not.

[midnight]

This is an older thread and I read most of it. After thirteen pages not much has been resolved. I occurred to me that powder coating has added another large group of variables to an already complex problem. I havn't seen any pressure tested data using powder coated bullets. I believe most of us treat powder coated bullets like traditionally lubed bullets, that is .001 to .002 over groove diameter. Is this necessary? It probably is since the coating is only .001 to .002 thick whereas a bullet's jacket is maybe .010 to .015 thick, sometimes even thicker. I jus thought I'd add a few more variables to the discussion.

Bob

[DougGuy]

Pressure occurs at a lot of places not just the initial curve. Magnum vs. standard primers, lot to lot variations in powder, PC as opposed to jacketed as opposed to cast, I would think boolit hardness would be one of the bigger factors, especially if cylinder throats are undresized, I don't think there is a common denominator in any of the pressure calculations.

You take each load and each gun, you figure out what to look for and you try some loads. Mostly they will all work if you are using published data like a loading manual, and you have signs you can look for if the load seems stiff in recoil, in almost any scenario, it will be the COMBINATION of things that cause over pressure signs.

I don't think there is much science in searching for a cast vs. PC vs. jacketed set of definitive answers since all that depends on so many other things.

[kreuzlover]

Western Powders are full of bovine excrement! All I got to say on the subject.

[fredj338]

Lead bullets can show higher pressures, just depends on the alloy & bullet design. A bullet with lube grooves will have less pressures than a solid bullet. this is easily proved over a chrono. There is a reason that substituting a lead bullet for a jacketed bullet raises vel, pressures a re going up. It would be nice if someone with a pressure trace would confirm all this.

[charlie b]

If you go back and read Gibson's posts on the subject. He has run pressure traces. Results are what was stated above. Sometimes jacketed are higher, sometimes cast.

Velocity does not always track pressure peak. You can have higher velocity at lower peak pressure if the pressure curve is 'flatter'.

[303Guy]

I was reading what someone wrote on the subject a few days ago and he was claiming that cast causes higher pressure. His reasoning was that less powder giving higher velocity with cast proved the point. I thought, "no it doesn't - it indicates less friction hence less powder and pressure to achieve the same velocity". But of course, that would be a wrong assumption too. It could mean that but it could also mean higher pressure. Only a chronograph used in conjunction with pressure trace equipment can say for sure. But it is an interesting topic. Thing is, at high load levels, strange things can happen like for example in a revolver, it is possible that the pressure as the boolit leaves crosses the forcing cone can bump the boolit up in the forcing cone causing a pressure spike.

What I found curious was the difference between a gas check boolit and a plain base bullet of the same design and weight.

[243winxb]

Photos of loading data comparing J & Lead. https://www.thehighroad.org/index.ph...d-bullets.265/

[Larry Gibson]

If you go back and read Gibson's posts on the subject. He has run pressure traces. Results are what was stated above. Sometimes jacketed are higher, sometimes cast.

Velocity does not always track pressure peak. You can have higher velocity at lower peak pressure if the pressure curve is 'flatter'.

This is correct and what I have found. Testing involved several handgun and rifle cartridges. Pressure in handgun cartridges (not rifle cartridges used in handguns) designed for use in handguns is more dependent on the seating depth of the bullet than on the material of the bullet. With rifle cartridges it appears (not stating that as a positive fact) the psi of a given load in a given cartridge is more dependent on the bullets actual bearing length than the material of the bullet.

Is pressure with a given load in a given cartridge in a comparison of equal weight cast vs jacketed bullets higher with one type or the other? "It is, unless it's not." Just one of those things in this game where there is no hard and fast "rule".

I have basically posted this conclusion on several threads. However, a complete "report" has not been posted because I still conduct further testing when I think of something that may give a conclusive answer. So far, there is no conclusive answer. And "old age" has nothing to do with it........

[KenH]

This is correct and what I have found. Testing involved several handgun and rifle cartridges. Pressure in handgun cartridges (not rifle cartridges used in handguns) designed for use in handguns is more dependent on the seating depth of the bullet than on the material of the bullet. With rifle cartridges it appears (not stating that as a positive fact) the psi of a given load in a given cartridge is more dependent on the bullets actual bearing length than the material of the bullet.

Is pressure with a given load in a given cartridge in a comparison of equal weight cast vs jacketed bullets higher with one type or the other? "It is, unless it's not." Just one of those things in this game where there is no hard and fast "rule".

I have basically posted this conclusion on several threads. However, a complete "report" has not been posted because I still conduct further testing when I think of something that may give a conclusive answer. So far, there is no conclusive answer. And "old age" has nothing to do with it........

Thank you for this post. I've came back to this thread a few times over the years hoping to see your results posted in a single post. I see (and understand why not) you've not made a single post yet. You have given use the info from your tests - so THANK YOU. It's sure surprising to me. I "knew" from years of casting & reloading lead bullets produced less pressure, after all, which do we use to slug a barrel? {g}

Thank you for your work.

Ken H>

[gumbo333]

Mr Gibson, I have followed your posts and comments/ testing for years with much interest. Your comment "old age" I assume is referring to you and not the lead boolit, but........

[DougGuy]

Pressure in handgun cartridges is more dependent on the seating depth of the bullet than on the material of the bullet.

Well, if one was just narrowing the comparison to only the cartridge in question, fired only in a test barrel, this would certainly be true. While not taking anything away from this factual statement, allow me to add that there are other factors that directly affect pressure in a revolver. Basically, anything that offers resistance, increases pressure. Cylinder throats being undersized is one of the main contributors of resistance, and *IF* there is more resistance offered by a hard cast alloy as compared to the exact same boolit cast in a soft alloy, then in this scenario, boolit material has a direct effect on pressure.

Is pressure with a given load in a given cartridge in a comparison of equal weight cast vs jacketed bullets higher with one type or the other? "It is, unless it's not." Just one of those things in this game where there is no hard and fast "rule".

Pressure occurs at a lot of places not just the initial curve. I don't think there is much science in searching for a cast vs. PC vs. jacketed set of definitive answers since all that depends on so many other things.

Same conclusion?

[303Guy]

A harder alloy might be expected to produce lower pressure all else being equal because it resists obturation better. But does it? Well actually sometimes it does. If a softer alloy is producing higher pressure then one should be looking for the cause because it might indicate something being wrong.

In using my 'test tube' that can catch a boolit fairly undamaged and 'reading' primer pressure signs, what I have found is that a softer alloy boolit can swage into the clearance between case neck and leade. This shows up as higher pressure on the primer (no pressure values are possible, only differences in pressure) and the obvious appearance of the recovered boolit. The pressure itself is not a problem - these are low pressure cast loads in a rifle. It's the boolit distortion and likely inconsistent pressure that might ruin accuracy.

[charlie b]

.......And "old age" has nothing to do with it........

Are you sure? LOL

[Cosmic_Charlie]

I recently loaded some warmer 44 mag loads. 20 gr. 2400 under a 240 XTP and was surprised how manageable it was. Also tried 17.4 gr. under a 250K boolit. That load really kicked. The alloy was softer than I had intended, less than 10 bhn according to the 3B pencil. I had been mixing what I thought was wheel weights 50/50 with pure. Lee tester inbound. Won't do that again.

[Larry Gibson]

DougGuy

"Basically, anything that offers resistance, increases pressure. Cylinder throats being undersized is one of the main contributors of resistance, and *IF* there is more resistance offered by a hard cast alloy as compared to the exact same boolit cast in a soft alloy, then in this scenario, boolit material has a direct effect on pressure."

That is an assumption I would have, and did, believe until I started actually pressure testing. With cast bullets in the 44 Magnum I haver tested the same bullet sized .429, .430. .432. and .434. In the 45 Colt the same cast bullet at .451, .452 and .454 was tested. Also in 357 magnum the same bullet was tested sized .356, .357, .358 and .360. In the 308W and the 30-06 I have tested the same cast bullet sized at .308, .309, .311, .312 and .314. All were the same alloy, same lube, same GCs (where used) and the same load. In all of those tests only the psi of largest sized bullet fell slightly above slightly above the test to test variation ES of the test. Then, even that slight raise was measurably inconsequential. The bullets were sized down within one bearing length of travel when the psi was still rising. Given it doesn't really require that much pressure to size the cast bullet what variation apparently falls within the shot to shot psi variation. Interestingly the chronographed velocities also did not increase beyond what would be normal test to test fps variation.

What about jacketed bullets? Well I've not run such an extensive test but in the 308W using 123/125 gr bullets of .307, .31, .311 diameter and 150 gr bullets of .307, .308, .311 and .312 diameter cup and core bullets all loaded over the same charge of the same powder I found no measurable increase in the psi as the bullet diameter increased. This test was done to test the safety of "mexican matching" milsurp ammunition. However, I did find that substituting a steel jacketed milsurp bullet with a steel core does increase the psi, sometimes dramatically.

I did an extensive test of the 45 ACP and 45 Colt cartridges in several handguns and a couple rifles loaded with the same cast 230 gr TC bullet with 4 different PCs vs the same bullet naked and lubed. The results of that extensive test has been posted on this forum. In that test I found no difference in velocity or pressure. I found the accuracy of the PC bullets to be on par not as good as the naked lubed bullet because of PC fouling in some of the firearms bores.

As to the psi of a given load with a given sized bullet in tight throated revolvers we should remember that the psi most often peaks after the bullet is completely in the barrel bore with a lot of the psi being vented out through the barrel cylinder gap. My conversations and comparison of measured psi data with another M43 owner/user who has put a strain gauge on a revolver cylinder (357 magnum) indicate that, with the same loads, the psi is a bit less in revolver. That would probably be due to the long cylinder throats (essentially "freebore") and the venting out through the barrel/cylinder gap vs the psi measurements taken is a closed breach system such as I use (Contender for pistol cartridges).

They say that "perception is reality" but in reality, it many times is not. As I've previously stated I have disproven many of my own concepts based on what I, and others, have perceived to be. It has been a real learning curve with the ability to actually measure most of the internal ballistics and much of the external ballistics. I continue to learn.

[Petander]

FWIW I've been playing with a 629 for some weeks now while waiting for tools from Brownells...

I have loaded a lot for it. Last week I reamed the ~ .4285" throats to .431". I just confirmed my heavy 335 grain (.4305") loads today, still the same velocity as before reaming. Same batch of ammo,same box.

Just my little unscientific observation. I was kind of waiting for a little velocity drop but no. Accuracy got much better right away,almost any bullet hits my 75 meter trap all the time now. I think fired brass comes out a little easier now...