It's only doing it with PMC. With Wolf Gold, Freedom Munitions reloads, and IMI M855, it functions fine, but with PMC, the bolt won't stay open on the last round, although it does fire every round. Am I correct in assuming it's due to PMC being weak ammo? Still annoyed that it does this, even with PMC.

PMC is weak-ish ammo, it is not unusual to not lock back if you are running a "full power" springs and buffers

PMC is weak-ish ammo, it is not unusual to not lock back if you are running a "full power" springs and buffers

 

+1 on what Vlad said.  Do you have a Full Auto bolt? Is your gas tube clean? Where are your ejected cases landing?

Need more info on your ejection pattern. Is the brass flying a few feet away or just dribbling out? My guess would be PMC being underpowered but generating enough pressure to cycle but not enough to push the BCG back far enough on the last round. In essence, short stroking. You could address this by running a lighter buffer or action spring. Or avoiding PMC

+1 on what Vlad said.  Do you have a Full Auto bolt? Is your gas tube clean? Where are your ejected cases landing?

+1 on what Vlad said.  Do you have a Full Auto bolt? Is your gas tube clean? Where are your ejected cases landing?

  

Need more info on your ejection pattern. Is the brass flying a few feet away or just dribbling out? My guess would be PMC being underpowered but generating enough pressure to cycle but not enough to push the BCG back far enough on the last round. In essence, short stroking. You could address this by running a lighter buffer or action spring. Or avoiding PMC

Yes, full auto bcg and cleanish gas tube. Brass is landing at 4 to 5 o clock consistently. It's definitely not dribbling out, even with pmc.

4-5 o'clock and you're wandering a little into short stroking territory. Take one weight out of your buffer and see what happens.

4-5 o'clock and you're wandering a little into short stroking territory. Take one weight out of your buffer and see what happens.

Will do. It's more 4 than 5 o'clock. Where should they be landing?

Will do. It's more 4 than 5 o'clock. Where should they be landing?

Actually, I think it was more 3 to 4 o'clock now that I think of it. I'll pay more attention next time out.

Actually, I think it was more 3 to 4 o'clock now that I think of it. I'll pay more attention next time out.