You did not mention what type of shotgun. If it is something you can not live with, then take it to a competant smith, and have it bent to the right spot, if it is a single barrel. Bending a barrel is an art, but there arepeople out there that can do it. Double's are much harder.

Changing or putting on a back sight is a band aid. If the barrel is bent, where ever you sight dead on, it will be different at another distance. Most people live with the handicap and learn how to aim their shotgun at different distances.

Just the fact that you are patterning your gun shows you are a serious shooter. Most people go into the woods never shooting their shotgun. Good luck. Tom.