Strange firing pin depth

[Fafhrd]

I have an MP10. other than furniture I have only changed the gas port in the barrel to .075 which made the firing ejection process stable and for the most part dependable. After firing two hundred fifty or so rounds today some rounds stopped firing. When I got the shell out it looked like the firing pin was not coming forward enough to cause the primer to fire. Only a small shallow dimple.

I cleaned the bolt firing pin, carrier etc and no change. Not all the time, intermittent. Could not find similarity with shells, brands, reloads or new. Just sometimes the pin doesn't come forward far enough.

Any suggestions as to what I can do?

 

[mtnwinds]

Your pin should protrude .060" plus or minus .005" from the bolt face. Someone may have a different suggestion but that's what I've always used for center fire rifle.

 

[Tbat]

Were you using the same brand of ammo or different brands? How do the primers look? Do they look like they are seated at the proper depth?

Although I haven't had any problems with my MP 10 firing anything that I have put in it, I did recently have a problem with some 7.62 x 39 in an AK that would not fire because the primer was seated too deep, two rounds out of the same box of ammo.