Purpose of Crimped Primer Pockets?


PDA






grant1265
October 6, 2011, 10:42 PM
May sound like a dumb question, but what is the purpose of crimping a primer pocket during manufacturing? Is it just to keep the primer in the pocket under battlefield conditions or what? BTW I found around 2,000 rounds of LC .223 at my local range, so I bought a Dillon SS 600. It'll be here tomorrow.:D

If you enjoyed reading about "Purpose of Crimped Primer Pockets?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
crkr
October 6, 2011, 11:35 PM
As someone else once said - to piss off reloaders.

But really it is to prevent popped primers during cycling of the weapon. Particularly AR based guns.

Walkalong
October 6, 2011, 11:36 PM
Is it just to keep the primer in the pocket under battlefield conditions or what?
Yep. It's to stop a primer from backing out and jamming a full auto gun.

amlevin
October 7, 2011, 12:22 PM
Take a look at NATO pressures in .223 and 9mm. The crimp is to keep the primer in place to prevent jamming of ALL firearms under combat conditions.

As for "POing" reloaders, I am always happy to take the crimped primer brass off anyone's hands that doesn't want it. I usually pick up a couple hundred rounds per week at the range. My Dillon 600 Super Swage has MORE than paid for itself.

rcmodel
October 7, 2011, 12:39 PM
It originally had nothing to do with NATO pressure, or the M-16.
Crimped primers were first used in military ammo for machine-guns 100+ years ago.

It carried over to all ammo then used in military bolt-action rifles of the time so the ammo could be used interchangeably in machine-guns and rifles.

Who did it first is probably lost in history.
But I imagine Dr. Richard Gatling, Hiram Maxim, or John Browning had a hand in it.

rc

USSR
October 7, 2011, 01:08 PM
It originally had nothing to do with NATO pressure, or the M-16.


+1. An interesting aside. I have once-fired .30 Carbine brass from many USGI manufacturers, dating from the early 40's to the mid-50's. In every case, only the Winchester made brass has a primer crimp, and even the Winchester brass manufactured several years before the advent of the M2 has a crimp. And the other manufacturer's brass remains crimp free even after the M2 came along. So, I have come to the conclusion that a primer crimp was never required for the .30 Carbine, and that Winchester did it only because, well, that's the way they did things.

Don

MtnCreek
October 7, 2011, 01:18 PM
An automatic rifle produces a lot of vibration on the firearm and ammo that a semi-auto does not. Primers can back out, pins can back out. A loose primer in an AR mag will jam it up tight!

bigedp51
October 7, 2011, 01:26 PM
grant1265

Military firearms have longer headspace than commercial firearms, "uncrimped" primers can rupture where the firing pin strikes the primer because the firing pin can act like a cookie cutter and punch the dent out of the primer.

Also note that military ammunition has crimped and sealed primers and projectiles to protect the cartridges from rough handing and the elements.

Below is an animated gif image showing a commercial "uncrimped" .303 British cartridge fired in a military Enfield chamber. Please note that military cases are thicker in the web area and as less prone to having case head separations. Also please note the words "headspace" and "head clearance" and note that "head clearance" is the "air space" between the rear of the case and the bolt face. "Head clearance" is how far a primer can back out of the primer pocket on a bolt action rifle and how far the case can stretch in the base web area leading to case head separations.

Watch the "uncrimped" primer move.

http://i122.photobucket.com/albums/o254/bigedp51/headspacestretch-1.gif

http://i122.photobucket.com/albums/o254/bigedp51/primers-a.jpg

SlamFire1
October 7, 2011, 05:22 PM
I thought I knew all the reasons for crimping primers, but in a recent Handloader magazine I found a new one.


These new lead free primers produce higher ignition pressures than the older lead primers. They apparently back out faster peening the action, the article was referring to pistol ammunition, so apparently they peen recoil shield faces and maybe auto pistol breech faces.


So manufacturers are crimping primer pockets to reduce peening.


What I am supposed to do when lead free primers are the only primer on the market, has not been determined. Guess we will all have to shoot factory ammunition.

More profits for ATK.

Walkalong
October 7, 2011, 07:20 PM
Same reason they have enlarged the flash hole in brass. To help keep the lead free primer put.

Michael R.
October 7, 2011, 07:34 PM
they were used to keep the primer sealed from weather and/or full auto fire

If you enjoyed reading about "Purpose of Crimped Primer Pockets?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!