AR15 lock back ammo sensitive?

[greg1147]

I built a clonish RECCE 15.1 FN barrel BCM upper receiver Colt BCG Gisselle wire wound spring H2 buffer. Runs as it should with a AEM suppressor
but I didn't take the suppressor last range trip and was just shooting 55 gr FMJBT normally 77 gr. The issue was no lock back after last round. Could this be
a result of running unsuppressed with a lighter bullet or just not suppressed. I need to get back with all my shit for a test run.
TIA

 

[Dev L]

Your very heavy spring and buffer combo combined with your gas port appears to be ideal for suppressed and undergassed for non suppressed... or over sprung and buffered for your gas port size unsuppressed... depending which way you want to look at it. I tune my rifles for light buffer, light carrier, and standard spring while unsuppressed. This offers very low reciprocating mass and very low recoil with a faster recoil impulse. The downside is slightly overgassed suppressed, but not bad. The low mass route is less reliable in adverse conditions unsuppressed. I can accept no lock back in adverse conditions unsuppressed and just keep my precision rifle clean and also accept the insignificant extra gas suppressed. Your set up is ideal for your set up if you eschew adjustable gas blocks. The high mass route is also more reliable and has less of a cyclic difference suppressed vs unsuppressed in full auto.

The 55 grain vs 77 grain won't amount to a hill of beans in difference, it is mostly theoretical. 5.56 vs .223 pressure has more effect. I have almost never had bullet weight result in a different gas block setting on my SLR or Superlative gas block builds, but comparing .223 vs 5.56 brass cased ammo of the same weight it frequently has 1 click difference.

 

[greg1147]

Your very heavy spring and buffer combo combined with your gas port appears to be ideal for suppressed and undergassed for non suppressed... or over sprung and buffered for your gas port size unsuppressed... depending which way you want to look at it. I tune my rifles for light buffer, light carrier, and standard spring while unsuppressed. This offers very low reciprocating mass and very low recoil with a faster recoil impulse. The downside is slightly overgassed suppressed, but not bad. The low mass route is less reliable in adverse conditions unsuppressed. I can accept no lock back in adverse conditions unsuppressed and just keep my precision rifle clean and also accept the insignificant extra gas suppressed. Your set up is ideal for your set up if you eschew adjustable gas blocks. The high mass route is also more reliable and has less of a cyclic difference suppressed vs unsuppressed in full auto.

The 55 grain vs 77 grain won't amount to a hill of beans in difference, it is mostly theoretical. 5.56 vs .223 pressure has more effect. I have almost never had bullet weight result in a different gas block setting on my SLR or Superlative gas block builds, but comparing .223 vs 5.56 brass cased ammo of the same weight it frequently has 1 click difference.

Guess that answers my question, more detail and tech that I expected. Back to the range. Thanks

 

[rmfield]

Guess that answers my question, more detail and tech that I expected. Back to the range. Thanks

The detail is important. Suppressed or not, gas port size and location, barrel length (dwell time), BCG weight, condition of gas rings, buffer weight, buffer spring strength, and finally just how dirty the rifle is, all play a role.

 

[greg1147]

The detail is important. Suppressed or not, gas port size and location, barrel length (dwell time), BCG weight, condition of gas rings, buffer weight, buffer spring strength, and finally just how dirty the rifle is, all play a role.

It's dirty, lot of rounds down the barrel since last cleaning and the OPS Inc AEM5 is a gassy suppressor.