One thing I’ve noticed on all my new builds is the standard milspec buffer springs these days are total crap and very raspy. I replaced all the buffer springs in all of my ARs with JP polished flattened springs, making sure to have carbine size springs and carbine buffers on my carbine length gas systems and rifle length springs and rifle spring buffers on my mid length and rifle length gas systems. This has improved my actions on my rifles immensely. I’ve also been running my bolts wetter using
either Teflon spray lube or “Duralube”. And I’ve gone back through every rifle to be sure the hammer face is stoned&honed to a mirror finish to reduce drag on the BCG. Also, I’ve double checked the bumpers on the back of the buffers themselves to see if the stock screw is kissing the buffers. If they are, I dremel off the excess. (My AR 450 Bushmaster had this issue with an excessively long screw causing the buffer to stop just shy of lock-up on the last round. These little nit-picky tuneups seem to have helped eliminate the questions of whether it’s a receiver issue or not. Now I can focus more on the loads themselves.