Military crimp

GI ammo has crimped primers to keep them from falling or blowing out in a machine-gun or full-auto rifle.

The crimp has to be removed before you can reload them, either by reaming or swaging.

They have nothing to do with accuracy.

You can see a ring depression around the primer on American GI brass.
European ammo may use three or more stab crimps around the primer cup.

rc

If you shoot NATO rounds (5.56 or 7.62 designated) you will see a circle in the brass around the primer pocket. You will not be able to seat a standard primer unless you swage to rmeove the crimp, or use a primer pocket former and grind it out.

There will be no question if you need to, you can't seat a primer if you don't.

found this out with white box 5.56 winchester rounds in .223 from midway. They had crimped primers, and I ended up needing the primer pocket swagger from RCBS to swage these cases so I could reprime.

If I recall, in addition to the circular ring around the primer, I think the NATO rounds have a little cross shape on the headstamp. Not sure if all crimped rounds have this or just NATO, but I am sure some of the expienced guys here will know.

and rc beat me to the post speaking of guys that would know.

Military ammunition will often have a crimp ring around the primer. Its there to prevent a primer from comming out and jamming up a weapon which can happen with non crimped ammo in machine guns and other open bolt weapons that are partuculary hard on ammo.

The crimp is usually visible or you find out when trying to insert a new primer and it either will not go without a lot of pressure the usually crushes the primer or mashes it flat without getting it in the pocket.

The crimp offers not other advantage and once the primer is removed the crimp needs to be removed in order to reprime the brass as it makes the pocket opening smaller preventing proper insertion.

The crimp ring is a thin amount of brrass and can be removed with a chamfer tool, old pocket knife, specialized pocket uniforming tool, press mounted primer pocket swaging tool, etc. The more expensive tools make the job easier and faster. For the occational piece of military brass the chamber tools are fine, for large quantities of military brass the press mounted swagging tools are better and less tiresome.

Besides the most common crimp... that around the primer as has been discussed above, there is another...

Some military rounds also crimp the bullet into the case. When reloading Lake City 223, you may find a ragged edge on the cartridge mouth due to military bullet crimp at the cannelure. This ragged edge is easily removed by standard case trimming, and, due to pressure issues, should not be duplicated on your reloads. The bullet is held more than adequately enough by the standard civilian neck sizing.

L-R = Not crimped, U.S. type Ring crimp, European type Stab crimp.
The lacquer sealer on the primer is often a sign the primer is also crimped in place.




rc

The Dillon swagger at about $90 is generally considered the best tool, with the RCBS coming in second, from what I'm reading here and elsewhere. These 2 tools actually move the brass around and reshape the whole pocket.

Most of the rest simply cut away the swagged area from around the pocket, leaving a beveled entry for the primer. You can do the same thing with a standard countersink cutter and a drill press.

I've the Dillon Super Swager. I've no regrets. I reload thousands of 223/yr and many, if not most has a military crimp. The Dillon does a great job removing the crimp on 95%. There are a few, however, even the Dillon can't remove. Those I toss.

I am a little cheap so I just use a drill and countersink, it works just fine for me.