I haven't seen a production rifle shoot 5" groups off a bench in many many years. Let alone two (or one that was returned and checked at the factory). I wouldn't be surprised if it is the shooting technique. Placing the barrel of a light sporting rifle on the bags at different locations and using different cheek pressure etc all can effect accuracy. Inconsistency is the best way to ruin accuracy. Could even be a flinch by the shooter. One way to find that out is have someone else load (or not load) the rifle, put it on safe and hand it to the shooter. See if he flinches when the firing pin drops on an empty chamber.