Guys,

I had a friend who had 3 cartridges misfire, out of a batch of 50-60. That was a bit much... He said the primers of the cartridges which misfired were hardly or not dented by the firing pin at all. I have yet to see a batch of both fired, misfired and loaded rounds.

Now, I'm aware there does not have to be ONE reason for problems like this. It could be any one or a combination of at least:
- too deep a primer pocket
- an out of spec primer (primers in question were CCI 250 Mag)
- too hard a primer cup
- too weak a main spring
- too short firing pin protrusion

At this very moment, without having seen the rounds which misfired, I'm sort of suspecting the primer pockets - simply based on the missing indent of the firing pin. Should that be the case, is there a spec for the dimensions of a primer pocket for large rifle primers - in particular depth??

Likewise, is there a spec for the dimensions of a large rifle primer??

- mike

Have you ruled-out crud around the firing pin?

Ninety-nine chances out of 100 it is a problem with the gun. One of the possiblities you failed to mention would be excessive headspace (short base-to-shoulder dimension) of the misfiring cartridges.

I highly doubt either "short" primers or an overly "deep" primer pocket. In 40+ years of reloading I have never run across either.

Thanks for the suggestions guys. It seems like you are both suspect gun as opposed to problems of the primer pocket dimensions. I shall certainly keep this in mind when I try to debug the problem further. I'll also compare the heads-shoulder dimension of the misfiring rounds with both fired and loaded cases, one more option. AR is an amazing place to tap into a bunch of experience

- mike

Excess oil around the firing pin can cause weak strikes. The oil acts as a buffer around the taper where the body of the pin begins to reduce.
Good luck!

A large pistol primer is shorter than a large rifle primer - usually.