223 case splitting... what causes this?


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stubbicatt
February 4, 2008, 09:00 AM
Hey guys. I've had this happen to me twice in 20 years of shooting. The round in the chamber fires, and then splits circumferentially about midpoint on the case body. Not a case head separation, but halfway to the shoulder from the case head. Rifle ejects the rearmost 1/2, and forces a fresh round into the remains of the first, still stuck in the chamber. Rifle quits running.

http://i80.photobucket.com/albums/j187/stubbicatt/IMG_0406.jpg
http://i80.photobucket.com/albums/j187/stubbicatt/IMG_0404.jpg
http://i80.photobucket.com/albums/j187/stubbicatt/IMG_0403.jpg
http://i80.photobucket.com/albums/j187/stubbicatt/IMG_0402.jpg

Any ideas? These photos are from my present HK 223 clone. I didn't take any photos from the exact same thing in my AR15, 15 years ago.

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taliv
February 4, 2008, 10:43 AM
i had that happen with one batch of ammo i made. frequency was about 2-3 occurrences per 100, and it happened in 3 different guns. batch was about 2000 rnds.

however, none of those split at the neck, and none of them show the weird pattern of lines and carbon that yours show. they were all otherwise normal.

i never figured out what caused it.

edit: while my rifle stopped, obviously, the case wasn't stuck, and the standard malfunction drill cleared it every time.

snuffy
February 4, 2008, 01:10 PM
however, none of those split at the neck, and none of them show the weird pattern of lines and carbon that yours show. they were all otherwise normal.

Those weird lines are from the HK FLUTED chamber.

Stubbi, that's probably caused by bumping the shoulder back too far. It IS case head separation, I've seen this several times before like that, but only on .223. They actually separate about half way up the side of the case wall.

stubbicatt
February 4, 2008, 06:50 PM
OK then.

I know that one can measure headspace of a conventional chamber using proper tooling, taking some cases fired in that chamber, and getting a reading. By conventional, I mean like a bolt action or even a gas operated, locking, action.

Can one measure headspace using as fired cases from one of these HK chambers? Thing is, that the fired cases fit right into one of the Dillon chamber gizmos that you can buy. I would have to compare it again to sized brass, but my *memory* says that the fired cases didn't grow.

So, what gives? A round from a machinegun, already stretched out and such, and then full length resized to fit the Dillon chamber, and then this? Why part at that point on the cartridge brass? The incipient case head separations I've seen before occurred at the web of the case.

I wonder...

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