I have a 20” Bartlein +1 6 Creedmoor, a 22” JP rifle length gas 6 Creedmoor, and a 22” Seekins 243 with standard rifle gas and run them all on the same lower. I use JP FMOS and an Armalite 7 3/4 buffer tube with rifle spring and H3 carbine buffer. I’ve run a LMOS carrier with lighter projectiles...