Firing pin protrusion?

[OldSoldier]

I am having a failure to fire problem with some ammo in my 6.8SPC, while other ammo from the same manufacturer fires perfectly. I have been communicating with the manufacturer and they are looking for the problem, however the problem seems to be related to primer depth (surface of the primer is below the base) and firing pin protrusion. I have not been able to find the specs for pin protrusion. I have measured protrusion from my 4 ARs and all 4 measure .030 +or- .001, however when I switch firing pins between rifles I am able to get another .00035 protrusion from one pin in the rifle in question. This helped reduce the FTFs but did not eliminate them altogether. The ammo that fires 100% has primers that are flush with the base, so one thing I am looking at is the firing pin, but I can't find the specifications and tolerance which are acceptable for ARs. If anyone has the figures or can point me to a source it would be very helpful. Thanks in advance.

Ron

[SOTIC1993]

what fire control system are you using?
I have seen many FTF from hammer strikes to soft?

if you have a complete lower from another AR swap them leave the firing pin alone and see what happens?

[stmcelroy]

Are you having any problems with pierced primers? I had an issue with my last 6.8spc.

[OldSoldier]

I have tried 3 different lowers, all have Wilson Combat TTUs. All three lowers fire 5.56 and 50 Beowulf without a hitch. The only ammo that gives problems is the stuff with primers seated below the level of the base. SSA is working with me on this and will work it out one way or the other.

No pierced primers at all, my problem is just the opposite.

Thanks for the input.

[SOTIC1993]

I will ask the obvious but is the head space correct?

[stmcelroy]

Who's upper is it?

Like I said previously, I had issues with a 6.8 upper and the ammo manufacture(SSA) was supposed to be the problem.

I met up with SSA and went to the range with them, shot their ammo through my gun and figured out it was a manufacturing error by guy who made the bolt.

If SSA isn't having widespread issues with their ammo, then it's probably the upper.

[OldSoldier]

The more I look into it the more I tend to agree that it is the upper that is causing the problem, however the first thing I noticed was the primers being seated below the base level of the ammo that was misfiring, but the ammo with primers seated flush fired 100% (SSA bulk ammo) so I thought it might be a firing pin protrusion problem. SSA is looking into it, but I really don't think that is where the problem lies. (They are great to deal with). I could send the upper back to Spikes, but where is the fun in that? If I can find the problem myself that would be more satisfactory, if not then I will send it back. (their CS is also great). I did find the protrusion specks so when I get time I will play with that.