Pierced Primers with an M-14...

[Tyler]

I went out today and shot about 40 rounds of South African surlpus 7.62x51 with my Norc M-14.

There were a few issues that popped up afterwards that weren't apparent during firing, everything on the rifle functioned fine:

1. 3 cases had pierced primers, the firing pin left a perfect firing pin sized hole in the primer. The rest of the brass/primers seemed quite normal with some exceptions...

2. On 2 casings there were some marks on the primer that worried me. It appeared as if the primer was double struck in two different places at first glance, but that's impossible. Upon closer inspection, the primer looks as if the firing pin was dragged across the surface of the primer, leaving a deep valley leading from the edge of the primer to the centre of the primer.

I'm guessing for now that the firing pin was stuck forward during chambering, causing the 'valley' across the surface of the primer as the round came up from the mag. The firing pin floats freely, and the back portion of it is intact. Any marks I should look for on the bolt/reciever?

3. I can clearly see the date stamp of one of the cartridges on the face of my bolt. It is etched in brass and won't come out with normal cleaning... could one of the rounds have been over-charged?

 

[Proutfoo]

I am no expert but this sounds very much like pressure problems.

headspace?

 

[Tyler]

Funny you mention that... I tried a rough guesstimation with my vernier calipers on some fired brass, and it did seem a little borderline on the tight side, but I could be way off.

That said, I have no problems with commercial .308... but after this episode I'm not too sure.

My bolt does move back and forth ever so slightly when it is in battery... is that normal?

EDIT: Tried my best measuring with some brass from today, it seems to be between 1.637 and 1.640. Wide margin of error... but that SEEMS to be OK.

 

[sunray]

"...is that normal?.." No. If it moves with a round in the chamber there won't be a proper seal. It's not likely that there's a headspace issue, but it wouldn't hurt to check it. Give the bolt a bath too.
I'd suspect the ammo first. Especially as you're not having problems with all ammo. SA ammo is usually good stuff, but you have no idea where or how it has been stored.

 

[Plinker]

Okay - I've covered this issue a few times, as it has happened to me. The problem is very likely that the gap between the firing pin protrusion and the hole in the bolt face is too large.

Remove your bolt, and carefully strip it. You will probably find funny pieces of metal in the firing-pin channel. This metal is from the "pierced" primers, and is actually primer metal that has extruded (under pressure) into the gap between the bolt face and the firing pin.

This extruded metal will eventually jam the firing pin forward, which might explain the funny markings you are seeing on the casings in the primer area. Eventually, the jammed pin can/will cause an out-of-battery firing, which is pretty dangerous (to put it mildly).

Please strip your bolt, and comment here on what you find. The presence of primer metal in the firing pin channel is proof that you are having this problem. If there is no metal, you can look for another cause.

If you are having this particular problem, the easiest solution is usually to replace your firing pin with a USGI pin, which will be a better fit.

 

[Tyler]

If you are having this particular problem, the easiest solution is usually to replace your firing pin with a USGI pin, which will be a better fit.

Phew.

Sure is cheaper than replacing the whole bolt!

Thanks for the advice!

 

[Tyler]

"...is that normal?.." No. If it moves with a round in the chamber there won't be a proper seal.

Sorry, I forgot to mention that it only does this with with an empty chamber.

 

[Tyler]

You will probably find funny pieces of metal in the firing-pin channel.

I stripped the bolt.... that was fun.... and I didn't find any bits of metal in the firing pin channel or on the firing pin at all. Just a good deal of very dry carbon. Maybe I should lube the firing pin channel better next time?

Here's a pic of the ammo:

The middle and right casings have the 'drag marks', which actually look wider in diameter than the firing pin mark itself.

Not the case on the left with the pierced primer, it too has a dent, only this time it is on the base of the case rim (circled), two casings surfaced like this. Maybe the brass was too soft for the ejector?

Maybe this is a feeding problem? Or is it just the ammo and I should stop worrying about my rifle.....

 

[sunray]

"...is it just the ammo..." Likely. Especially if you're not seeing this with all ammo. You're not likely to be easily finding much surplus SA ammo anyway. It has nothing to do with feeding though.

 

[carbonrod]

I am not sure about some of the other symptoms that you mention -- date stamp etched in bolt, but pierced primers with South African out of an M14 is normal. When I first saw it on mine I was also freaked out. I asked a bunch of people a bunch of questions. Ultimately, when I shoot this ammo out of my M305, I get many pierced primers. When I shoot it out of my LTR, I get no problems(other then bad groups). When I shoot any other ammo(factory, or hand load) that I have tried out of my M305, no problems.

Also, if I look at the brass after anyone else has been shooting this stuff, they will also have many primer punches, and backed out primers.

I have to think that it is just that this ammo sucks.

 

[Fire]

Yeah I have the same problem with SA more than half of the primers come out peirced but it doesn't do it with any other ammo. My solution is not to shoot anymore SA.

I have never had the problem with the other marks on the primer though. Not sure what that is other than the possibility the peice of brass that gets fired out when the primer is peirced is getting stuck between the bolt face and the next round. I know I had found several small round peices of primer after I shot it.

 

[tiriaq]

...I have never had the problem with the other marks on the primer though. Not sure what that is other than the possibility the peice of brass that gets fired out when the primer is peirced is getting stuck between the bolt face and the next round. I know I had found several small round peices of primer after I shot it.

I was wondering the same thing. When a primer is perforated like these, there is a piece missing; often the pieces will be back inside the bolt - which can create a very dangerous situation - but they weren't in the bolt in this instance. If they got trapped between the boltface and the cartridge, the primer could be marked in this way.

I have no experience with this ammunition; if the primer failures are occurring only with this one make, the obvious solution is to not use it in this rifle.

 

[44Bore]

The drag marks are from the fireing pin being forward as the case starts to eject--this was an issue on some of the earlier .40 S & W pistols and was caused by the slide unlocking too soon--lighter loads or stronger recoil spring was the cure in the pistols. The pierced primers may be a dimensional issue with the ammo--as in the shoulder is slightly too far back on the case--this was an issue with some of the norc .223 ammo that I used a while back--showed up in some rifles but not all that I used the ammo in.

The drag mark is the one I wopuld be concerned with as it will eventually cause the tip of the firing pin to fail.

44Bore

 

[Tyler]

The drag marks are from the fireing pin being forward as the case starts to eject--this was an issue on some of the earlier .40 S & W pistols and was caused by the slide unlocking too soon--lighter loads or stronger recoil spring was the cure in the pistols.

AH HA!

That seems to be the issue... I tried the 'spent .30-06 casing' method for stripping the bolt down. When I went to re-assemble the bolt, the mainspring could not over power the ejector spring, so I had to hold the bolt forward while I re-assembled it.

What do USGI springs go for?

 

[tiriaq]

The situation with a rotating bolt rifle is not the same as with a tipping barrel pistol. In your M305, as the bolt rotates to unlock, the tail of the firing pin, at the rear of the bolt, should be in contact with the cam surface of the receiver, and should be retracted by the camming action. Field strip your rifle and slowly cycle the action. You should be able to see the firing pin being retracted. Once the bolt has rotated to unlocked position, the firing pin should be out of contact with the primer. It is not unusual to see firing pin drag marks on cases fired in some tipping barrel autoloading pistol, but this is a mechanically different situation.
You could also check to see if there is any way that the ejector could contact the primer, but I doubt that the ejector could make contace with any portion of the casehead theat close to centre.