Bullet Crimp

 Cast Bullet Crimping

Crimping of Handgun Cartridges

I have loaded thousands of handgun cartridges since 1955. Mostly .38 spec, .357 Mag, .41 Mag, .44 Mag, .40S&W, .45ACP, 9mm. 99% were cast bullet loads. 99.99% of those loads had the case mouth crimped tightly on the bullet.

There are many reasons for crimping:

Improves consistency of ignition
Increases velocity
Decreases velocity variations
Improves accuracy
Holds the bullet in its proper place in the cartridge case
Prevents the bullet from being forced into the case during the feed cycle.
Prevents the bullet from being pulled out of the case mouth by recoil

I have crimped and not crimped. I have tested for accuracy and for velocity consistency with and without crimping.

I believe crimping of cast bullets to be necessary for consistent performance. I have never crimped jacketed bullets in either handguns or rifles.

Lightly crimped cases can last 40 years or more with untold numbers of reloads. They will eventually split lengthwise on one side ( about a half inch ). Using 40 year old cases loaded to .38 special pressures, I get about one split case per 500 rounds. You will not know the case split until you eject it. The split round will hit where you were aiming and there will be no noticeable gas leakage.

The only cartridge I have found that MUST have a heavy roll crimp is the .44 magnum used in a revolver. This is not just for ignition but to prevent the bullets in the unfired cartridges from moving forward under recoil and locking up the cylinder.  I have no experience with anything larger than the .44 Magnum but this same crimping requirement would apply to all of them.

Heavy roll crimps, unlike light rolled crimps, really ruin cases quickly.

In some handguns, with cast bullets a thousandth or two oversize, or with thick case mouths, or with a small chamber, failure to crimp can result in a failure to be able to seat the cartridge fully in the chamber. As well, these same issues can prevent chambering even with a proper crimp.

In my own loading, I apply a very slight roll crimp, (barely visible), to revolver cartridges and a slight taper crimp, (not visible), on autoloader cartridges like .45ACP or 9mm. To check the crimp, try the first ten or twelve cartridges in the chamber they must seat fully and easily with no pressure. I field strip autos and use the barrel as a gauge to check the crimp and overall length. ( I don't feel comfortable cycling live ammo through an autoloader at home.) I don't have this problem with revolvers since I don't have to close the cylinder. If you don't have the gun to check them, you can use a dial caliper to check the case diameter at the mouth and immediately behind the crimp to the case diameter measurements published in the loading manual.

When checking revolver cartridges, also check to be sure the bullet does not extend
beyond the front of the cylinder.




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