Hay people that is the gas screw, not a plug. It is not necessary for any loads factory or military below 180 grains! The M1 rifle was developed in the mid 30's for M1 ball ammo that is 173 grain bullet. M2 ball didn't appear until late 1939. Op-rods were made from 4140 steel and don't bend as alleged in the online forums. All commercial hunting ammo either 150, 165. or 180 are safe even Superformance. After market gas screws are not needed.
