Pierced Primer Problem

[AR-10]

Out shooting my AR-10 today.

Hirtenberger 7.62X51 Ball ammo. Manufactured 1979. Picking up the brass, I found two casings that had pierced primers. The circle where the firing pin struck the primer was cut half way around the edge, and pushed back out far enough to stick out. When I glanced at the first one I picked up, I thought the firing pin had broken off in the end of the casing.

Upon examining all the brass I fired today, it appears that most, but not all, of them are being hit too hard. Many of the primers look like they are being hit with a flat nosed pin rather than the round nose that is still on the firing pin. Some of them are being punched almost clear through, and have a very distinct sharp look to the edge of the divot. Others look normal.

I keep the firing pin generously lubed with Break Free CLP. However, I have had it out shooting three times, for a total of about 150 rounds since it was last cleaned and lubed, so I doubt that it is dripping with lube today.

Am I over-lubing, or is there some other problem going on here?

 

[Pampers]

You're not "overlubing."

Does this problem occur with any other "name brand" of ammo? If not, you've found your problem.

The first thing that I would suspect is excessive headspace. Is the shoulder of the fired case noticably forward of where it is on an unfired case. There are several headspace gauges available.

Second suspect is a soft primer which is being extruded into the firingpin hole. I'm not familiar with your ammo. I haven't shot anything except handloades in decades.

The last thing thaqt I'd look at would be an oversized firingpin hole in the bolt face. If it is oversized, it could be fixed with a bushing by any competent gunsmith.

Finally, this is not a great safety hazzard. The gas system of an AR-10, or AR-15/M16 for that matter, do quite a good job of handling the gas from a pierced primer.

But, once again, the first thing that I'd suspect is the ammo.


Yr. Obt. Svnt.

 

[AR-10]

Thanks for the quick reply, Pampers.

I don't have a caliper to measure with, but the fired brass is very nearly the same size as an unfired cartridge. the mouth is slightly larger, and the overall length has increased by one or two hundredths, I would guess.

I save most of my brass, so I dug out a couple different brands and looked at them.

The Hirtenberger is German, and has a siver colored primer. I have some Winchester and some Portugese (FNM) that both have brass colored primers. The indents on the brass (?) primers is not quite as deep, so it could be soft primers.

I looked through all the Hirtenberger brass I have shot, and found a third pieced casing, out of 180 rounds. Maybe I should go back to buying the Portugese. Three rounds out of 180 may or may not be a problem.

If, say, one of every hundred rounds gets pierced, will it erode the tip of my firing pin? It is a factory steel pin, not titanium.

Thanks

 

[Nukem]

Check the firing pin protrusion (with the bolt rotated closed in the carrier).