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

[kreuzlover]

I read some comments by Elmer Keith, in an old article long ago, and he stated that the reason he liked plain base bullets was because gas checks RAISED pressure. I don't know if he had H.P. White labs run comparison tests or not, but he used them a lot back then. He certainly did NOT like gas check bullets! Just thought I would throw that little tid-bit into the mix.

[fredj338]

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.

The less friction thing gets tossed out often but think about it, less friction means less pressures. At least with moly coated, less friction bullets, you have top add powder to get more vel. Lead bullets are more malleable though, easier to push down a bore, but also seal the bore better. So no free lunch on pressures vs vel.

[mehavey]

Hodgdon data for 45 ACP.
"Intellesting...." No ?

[Larry Gibson]

Hodgdon data for 45 ACP.
"Intellesting...." No ?

Any attempt comparing psi to CUP pressure measure is a futile exercise....apples to oranges...

[DougGuy]

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.

So these tests used the same alloy, but progressively larger boolit diameters. My comment was pointed at me thinking that a harder alloy would provide more resistance to swaging into the cylinder throats, thus raising pressure, as compared to the same boolit and same boolit diameter, cast in a softer alloy.

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.

Ok, logical, which would seem to reaffirm what I said in the comment above this paragraph comparing two different alloy cast boolits swaging into the same tight throats, and now you are saying that there was a very noticeable variation in pressure between two jacketed bullets, one with gilding metal jacket and lead core, and one with steel jacket and steel core.

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.

Since this thread was about comparing pressures of j words and cast boolits of the same weight, my opinion was/is that as alloy is harder, pressure would show a measurable variation attributable to the BHN of the alloy itself, not necessarily the same alloy with different coatings.