You didn't mention what kind of gun, or if you are useing choke tubes and do they all shoot to the same POI.

Some guns have shimms in the stock which help a little, maybe. A shotgun bbl can be bent, so can the stock, sometimes the choke threads are not installed squarely with the bore and quite often, the gun simply does not fit you. If you are shooting it off the bench, try just standing and shouldering the gun, shotguns are not aimed, they should shoot where you are looking. Sitting and shooting off a bench often produces different results then when you are shooting off-handed. Sorry, I can't begin to describe what goes into fitting a scattergun to a shooter, go to a skeet/trap range and ask around for a good shotgun smith.

Doug