My solution was a 0.100" gas port, a standard carbine buffer, and a JP polished standard carbine recoil spring, combined with a Superlative Arms gas block tuned in restrictive mode to barely lock the bolt back with unsuppressed supersonic and suppressed subsonic (was basically the same value for 100% reliable lock back with all magazines). Won't lock back on the last round with most unsuppressed subs, but will cycle them 100%.
I figure if I am shooting unsuppressed and get down to my magazine of subs, it is my last magazine anyway. Who cares if the bolt locks back on your last mag?