I went shooting with a friend yesterday and he brought his M1. Rifle did what I would say "short-stroking" as it chambered and fired but the op-rod did not go back far enough to pick up the next round and chamber it although it did cock the hammer. We checked to see if the gas plug was tight (it was), we checked to see if the plug was free of carbon (it was) and we checked to see if the hole was plugged up by carbon (it was not). Ammo was military and some reloads which he said worked fine in two other M1's that he owned. Any idea what could be causing the problem and any suggestions on how to correct it? Has this ever happened to you or anyone else who shoots the M1's? Any help by all would be greatly applauded. Thanks in advance.