Tom:
Recoil "rotation" may be influenced mostly at the butt, but I am talking about is lateral rotation or rotating around the center of mass which runs right down the middle of the side by side double between the barrels. When you fire the right barrel, the gun recoils upward but also trys to rotate counter-clockwise when viewed from the butt end. The reverse is true for the left barrel, it will try and rotate clockwise. The fact that the gun is against your shoulder can not compensate or stop the rotating completely.
Early on when I started making rifle conversions, I got the bright idea of machining two laser pointers to just go down each barrel at the muzzle and superimpose them on an object across the street from my shop. When I had that accomplished, I made up the correct spacers and soldered them in, thinking that I had achieved the ultilmate in rifle regulation. But when I shot the gun, they were nowhere close to right because of the lateral rotation or twisting of the double.
Because the bores of an over and under rifle are stacked one above the other and in line with recoil., you don't have the twisting rotation to deal with. I had suspected this but had not confirmed it till I actually got to doing a double stacked barreled gun. What think will affect the point of impact is weight added to any place other than the center of mass such as a heavy scope and mounts. How much this affects it, I don't know yet, but I will soon. I will tell all of you this though, the heavier the bullets and bigger the bore, it seems like to me, the less the point of impact is affected. The big heavy bullet rifles tend to be much easier to regulate than the smaller lighter bullet rifles. Also the bigger bores are more forgiving of bullet weight and speed changes in loadings. Bob H.
