Have a brand new 7600 in 308 it does basically the same thing. These rifles have rotary bolts and the recoil and the pressure of the round going off cause it to move rearward. I'm not saying that yours may not be worn some, but it seems to be the nature of the Rem. pump rifles, in my opinion. Mine is truly accurate and most pump Rem are. If your rifle locks up fine on a round, shoot it and have fun.