After cleaning it up with Hoppes No 9. (Bore and Gas Tube) I apply Super Lube synthetic grease to the bolt and carrier, just to the parts that slide on the receiver, don't lube the bolt itself (firing pin). It should rattle if it is not the spring loaded one when you shake it back and forth. You can use oil as well but I find the Grease does the trick and when cleaning up after it wipes off easy. Don't oil the piston or gas tube inside. I just wipe them down with a bit of oil to clean them up.