I'm experiencing POI shifts with a 338 RUM going from bench rest, to bi-pod, to shooting off my pack. I believe the main cause is recoil effecting POI before the bullet exits. My theory is that shooting off my pack allows the rifle to kick straight back, but on a bi-pod it "rocks" back allowing the butt to move down and the barrel to point up, and off the bench rest its causing muzzle rise as the gun has no where else to really go. All 3 positions are printing sub MOA groups, but each position is shifting the "zero'. Bench POI is highest, followed by bi-pod, and shooting off my pack is the lowest POI. (All shots taken with front hand holding the forearm. POI change is about 6 MOA from Pack to bench. Some people on here claim to have experienced similar issues, while others say that its impossible for recoil to occur before the bullet exits, so it must be parallax, flinch, body positioning or something else. The rifle did this with the factory synthetic stock and also with a wood stock that is piller bedded, glassed and floated. I don't experience this with lesser recoiling rifles. I'm not an elite marksman and this rifle is a challenge to shoot (with over 50lb's of recoil). I did qualify expert marksman in basic training on my first attempt, my Grandfather was on the army shooting team and taught me well, but that was long ago and I'm just getting back into shooting a lot, so I won't rule out shooter error, but I think I've got the fundamentals down since this isn't happening with my little guns. Anyone have any insight as to whether or not recoil occurs before the bullet exits?