Crimps. There are two types of crimp. Taper crimp and Roll crimp (which turns the mouth of the cartridge case into the sides of the bullet, usually into a crimping groove put there for that purpose. Your bullets (Hornady XTP) does not have such a groove. Roll crimps are generally used with revolvers and certainly only with cartridges with a rim diameter larger than the diameter of the case body.
45 ACP should NOT HAVE A ROLL CRIMP if they are intended to be fired in a semi-automatic gun.
Cartridges that headspace on the case mouth should NOT HAVE A ROLL CRIMP. They should have a Taper crimp Cartridges that headspace on the rim are indifferent to having a roll crimp or taper crimp as far as fitting in the chamber is concerned.
Your 45 ACP cartridges do not have a rim, per se. What looks like a rim is actually the result of a groove in the base of the cartridge so the extractor can pull the cartridge case out of the chamber.
If you did put a roll crimp on your 45 ACP cartridges, you may find that they go into the chamber too deeply for safety.
To test, take your barrel out of your gun and drop the cartridges into the chamber. They should fall in with a pleasing thunk and fall out with the pull of gravity. They should, if pressed in with your finger, not go in any further than they fell under gravity alone. (Probably flush with the barrel shroud, but this can vary with different models of gun). If there is any uncertainty, put one of your uncrimped (presumably taper crimped) rounds or a factory loaded round in the chamber and compare.
A light roll crimp might not give you any trouble with too-deep chambering, but it is best not to tempt fate.
A taper crimp is generally enough to grip the bullet strongly and since the taper tightly grips the bullet with the case mouth, prevents the bullet from being shoved deeper into the case when it hits the feed ramp during chambering in the normal course of firing.
If a round does have too much of a roll crimp to safely headspace, it may still fire because the extractor holds the round against the breechface, but it is best not to depend on that. Tempting fate again. If the round goes too deep and the extractor does not engage the extractor groove, you have a jammed gun, as the firing pin will probably not reach the primer.
If your roll-crimped round goes sort of too deep into the chamber and the firing pin does hit the primer, the case head may separate from the case body because it is not supported by the breechface. You have an explosion in your hand and face. Hopefully, most of it goes down the magazine well and you don't get too many splinters (if you have wooden grips) in your gun hand.
I think all your loads are lower than dangerous levels, but the 3.4 grains may not be enough to drive the bullet all the way out of the barrel. THIS IS VERY DANGEROUS if you fire another round. A barrel obstruction (like a stuck bullet) can stop the next bullet in its tracks, leading to a bulged barrel and maybe a burst barrel and perhaps a handgun that spontaneously and spectacularly disassembles in your hand. Can take fingers with it, too.
I suggest you disassemble those rounds. If you choose to shoot them, shoot them one at a time and check the barrel after each one unless you actually SEE a hole appear in the target. Or see the rounds go downrange, which at the speeds I expect with 3.4 grains might be slow enough to see, probably around 500-600 fps.
Cartridge length depends on two things. You don't want them so long that they don't fit in your magazine or cycle through your action They should not be so short that the volume under the bullet (where the powder sits awaiting ignition) is so small that the pressure when the powder does ignite goes up too high. A small decrease in that volume makes a BIG increase in pressure.
Generally, changing brass is OK with the 45 ACP, but if you are near either extreme, it is best to go carefully when making the switch. The 45 ACP is a forgiving cartridge, as it was designed over 100 years ago and runs around 20,000 psi. Modern guns, modern steel. Don't push the envelope, but don't shy away from a little experimentation either.
If you can, post pictures of the crimps on your rounds, please.
Last edited by Lost Sheep; January 30, 2012 at 12:50 AM.