Protruding primers

[hobberdobber]

Hi all. I had an M1 Carbine re barreled with a new Criterion barrel. I've shot it 6 times with 3 different ammo. The primer on the LC72 protrudes by .017-.019 thousands after firing it. I fired two rounds of LC72 - 3 rounds of RA52 and 1 round of VE S 7.62 2-63. Only the LC72 had a problem. It seems to me its the ammo. Has anyone had this problem and is the ammo safe to fire or should I take it apart and re-primer. I don't think the ammo is a reload. The ammo is "Lot LC=50-211

Information

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[Patrick Chadwick]

The speed at which a primer detonates means that the primer will move back before the base of the case. With a load in the normal range, the primer will move back on detonation, and a fraction of a millisecond later the main charge will ignite, the case expands to grip the walls, the case streches, and the base moves back to press against the bolt face, thus pushing the primer back into the pocket. An excessive charge will cause the primer to be moved back and expand around the chamfer on the primer pocket, but when the base is forced back, the primer, which is now oversized on the "corner" will nevertheless be forced into the pocket, thus creating the flattened primer look that indicates an excessive charge.

But if the primer is not forced back into the pocket, then the base did not move back fully to press against the bolt face. I.e. the case did not stretch sufficiently. However, the neck must have expanded enough to grip the chamber, otherwise the entire case would have moved back, and you might see a lot of soot around the case neck but no protruding primer. Not a simple yes/no answer - there will probably be cases with more or less primer protrusion and more or less soot.

Possible causes: the charge is on the low side and/or the case is too short and/or the chamber is too long! Check the case length before firing for the type of cartridge that has this problem AND the case length after firing of cartridges that performed satisfactorily, where we may assume that, after firing, the case stretched to the maximum length for that chamber. If there is a significant difference (here we need a carbine expert to say how much would be significant - my guess is more than 0.020") then the cases are too short for that chamber. Of course, if you are shooting old surplus ammo, then the powder may have lost a bit of "OOMPH". More than one factor may be involved here.

My experience up to now has been that old surplus ammo can cost more in wasted range time than it is worth. Measure, judge, and act accordingly.

[browningautorifle]

It seems to me its the ammo.

Sometimes ammo that's not stored correctly can have issues. Patrick gives you a blow by blow that you maybe don't want to get so involved in, maybe just segregate the ammo and find out if your right. Then it's not so much the primers, as it maybe the charge that's to blame. I'd just chuck the powder and primers and keep the bullet and cases.

[hobberdobber]

Thanks for the info. I went thru all the ammo & found that I have 2 unmarked boxes of assorted head stamps. My remaining ammo is head stamped LC 72 an all boxes are LC imprinted. I fired 2 rounds from this ammo & it showed no problems I could see or had knowledge of. I was told the VE headstamp is French an may be corrosive. I am taking the carbine down for a complete cleaning. The 2 boxes of assorted ammo will be demilled.

Thank You

Pete

[browningautorifle]

Assorted headstamps...maybe reloads? These could certainly be the problem. The major components are good value. The powder load and primers are small potatoes in this case...

[Patrick Chadwick]

Patrick gives you a blow by blow that you maybe don't want to get so involved in,

OK, I'll put it as succintly as I can:

IMHO tatty old ammo is ACWOTAM.