Its all about the recoil plate. There is some fitting to be done on the M1A1icon stock. Very few carbines these days are actually set up correctly in this respect, with the plate holding the action too high or letting it flop into the barrel channel - yours is a flopper in the M1A1 stock. You'll have to read up on fitting the action in that stock as the recoil plate is different than the regular stock. The fix will probably involve a hammer. . You're somewhat hampered because you don't want to mess up the regular stock fit so you can't do anything to the tang on the back of the receiver. On any carbine you should be able to grab the barrel with one hand and the stock with the other, try to push and pull the barrel and get no movement.