Ya got 2 different things going on brother 1 has nothing to do with the other.
I have an M5 setup 16" mid-gas upper has Nickel boron BCG and an Aero receiver, spring, and buffer.
I had some FTE/FTF issues and went to a complete Armalite set up. That seems to be the fix. I have RRA 20" rifle gas with a carbine setup without issue.
.308AR's unless it's a pistol is either mid-gas or rifle.