Cast vs Jacketed Load Data?

[Kosh75287]

Except for the explanations already offered, I don't know how to explain the difference between load data for jacketed vs. cast projectiles. However, there are a few assumptions I make, when comparing data for one bullet type, to arrive at data for the other:

1.) All other factors being equal, bullets cast from homogenous lead:tin:antimony alloy will tend to create less friction against the barrel than projectiles that are jacketed in gilding metal.
2.) Cast bullets that are polymer coated will tend to exhibit still less friction against the barrel than uncoated conventionally lubed cast bullets. Depending on the cartridge and pressures involved, I usually observe a 2% - 5% increase in velocity, all other load characteristics being equal.
3.) Given equal bullet weights/diameters/lengths, a given charge weight of propellant will tend to produce lowest velocities with the jacketed bullets, followed by the conventionally lubed cast bullets, followed by the PC'd bullets. Pressures tend to run in the opposite direction.
4.) Given identical bullet weights and configuration, jacketed bullets will tend to be longer than cast bullets, because the gilding metal jacket has lower density than the lead alloy. Longer bullets mean greater seating depth, which means less unoccupied space in the cartridge. This can translate to higher pressures. In larger capacity cases, this difference may turn out to be negligible. In smaller-capacity cases, a slightly greater seating depth can mean a radical increase in chamber pressure with attendant unfortunate results.

[hermans]

Except for the explanations already offered, I don't know how to explain the difference between load data for jacketed vs. cast projectiles. However, there are a few assumptions I make, when comparing data for one bullet type, to arrive at data for the other:

1.) All other factors being equal, bullets cast from homogenous lead:tin:antimony alloy will tend to create less friction against the barrel than projectiles that are jacketed in gilding metal.
2.) Cast bullets that are polymer coated will tend to exhibit still less friction against the barrel than uncoated conventionally lubed cast bullets.
3.) Given equal bullet weights/diameters/lengths, a given charge weight of propellant will tend to produce lowest velocities with the jacketed bullets, followed by the conventionally lubed cast bullets, followed by the PC'd bullets. Pressures should run in the opposite direction.
4.) Given identical bullet weights and configuration, jacketed bullets will tend to be longer than cast bullets, because the gilding metal jacket has lower density than the lead alloy. Longer bullets mean greater seating depth, which means less unoccupied space in the cartridge. This can translate to higher pressures. In larger capacity cases, this difference may turn out to be negligible. In smaller-capacity cases, a slightly greater seating depth can mean a radical increase in chamber pressure with attendant unfortunate results.

Excellent explantion

[Larry Gibson]

Except for the explanations already offered, I don't know how to explain the difference between load data for jacketed vs. cast projectiles. However, there are a few assumptions I make, when comparing data for one bullet type, to arrive at data for the other:

1.) All other factors being equal, bullets cast from homogenous lead:tin:antimony alloy will tend to create less friction against the barrel than projectiles that are jacketed in gilding metal.
2.) Cast bullets that are polymer coated will tend to exhibit still less friction against the barrel than uncoated conventionally lubed cast bullets.
3.) Given equal bullet weights/diameters/lengths, a given charge weight of propellant will tend to produce lowest velocities with the jacketed bullets, followed by the conventionally lubed cast bullets, followed by the PC'd bullets. Pressures should run in the opposite direction.
4.) Given identical bullet weights and configuration, jacketed bullets will tend to be longer than cast bullets, because the gilding metal jacket has lower density than the lead alloy. Longer bullets mean greater seating depth, which means less unoccupied space in the cartridge. This can translate to higher pressures. In larger capacity cases, this difference may turn out to be negligible. In smaller-capacity cases, a slightly greater seating depth can mean a radical increase in chamber pressure with attendant unfortunate results.

Yes, they "should". However, after many attempts to prove this assumption through actual pressure testing, I have been unable to prove that assumption correct one way or the other.

Sometimes, with all else equal as close as we can make it, the pressure and velocity are higher with the jacketed bullet and sometimes the pressure and velocity are higher with the cast bullet. Thus far in testing, I've not been able to determine any hard or fast "rule". As I've stated numerous times before on this topic; "it just depends" which will give higher velocity and pressure with no indication which way it will be.

[dondiego]

Yeah. Just don't shoot your eye out kid.

Very Christmas appropriate!

[Kosh75287]

Yes, they "should". However, after many attempts to prove this assumption through actual pressure testing, I have been unable to prove that assumption correct one way or the other.

Oh, I agree that the trends I describe are not "everytime things". But I see them more often than not.

Since you have access to equipment that can measure chamber pressures, I'll defer to your considerable experience in the matter, and your greater capability to quantify it. I nonetheless see the effect I describe when reloading rounds having an operating pressure north of about 28,000 p.s.i. MY "pressure indicators" are primer deformation compared to factory ammunition and (with auto pistols) slide velocity as measured indirectly by case ejection compared to factory rounds.

In 9mmP, .38 Super, and .357 Magnum, I can all but bet the rent that the effect I described in my previous post will show up. I SOMETIMES see it in .40 S&W, but not always. I NEVER use loads that give primer deformation signs in .45 ACP (perhaps .460 Rowland?), but case ejection distance vs. factory is still a fairly robust indicator.
I have seen SUGGESTIONS that the effect I describe was happening in Ruger/TC only loads in my .45 Colt Redhawk. The last time I saw significant primer flattening, observed velocities had such high SDs that the results were equivocal. In truth, I can usually obtain the upper performance level I desire from my .45 Colt RedHawk (250-260 gr. @ 1250 f/s) without deforming primers. With Alliant 2400 or one of the 4227s in a 7.5" barrel, it's not difficult.

I guess that if you and I were to run my loads for the cartridges mentioned through your pressure measuring equipment, we just MIGHT find that the pressure trend I describe is more apparent than real. I can only relate what I'M seeing, and how I interpret it. But I don't think that the way I am interpreting primer deformation and slide velocity (ejection distance) is without foundation.

Before posting my message previous to this one, I meant to add that one of the older SPEER manuals related an incident in which a 9mmP handload that developed ~29,000 p.s.i. at one o.a.l., but chamber pressures either approached or exceeded 60,000 p.s.i., when the o.a.l. was shortened by a small amount (0.015" or 0.020", if memory serves). I think this was part of the precautionary articles in SPEER #9, #10, or maybe #11.