In the ending scenes where Krader is shown shooting his rifle, even though we hear the blast of the rifle and see him pull the trigger, yet there is no recoil(kick) from the rifle at all. It is very obvious that the actor is not shooting the rifle.
He was plinking bottles with it earlier in the movie. That leads me to believe that it was a .22 caliber rifle (which has very minimal recoil). Not many people would plink bottles with i.e. a .30/.06 deer rifle.