Have you patterned the guns? I sometime shoot my pigeon guns and they shoot high. So I know to adjust where I shoot the target at.
I patterned the Greener single barrel trap gun and at about 15 yards the main charge of bird shot was 4"-5" was low at 4:30. If I'm visualizing it properly I would have to hold 4"-5" at 10:30, pretty much obscuring the bird.
I think there are 2 problems to be discussed here. Whenever I've gotten a new shotgun, I have always started by shooting it off sandbags just like a rifle to see if POI matches up with POA. Most of the guns I've acquired in recent years were for turkey hunting, so it's essential for the gun to shoot straight. Most SxS shotguns are regulated for field loads, and they will not center the heavier turkey loads. A SxS is usually going to have L/R issues, while an O/U will often have Up/Down issues. The Dremel tool solution already mentioned can correct this, though I have just used a round file to center the pattern of several guns. It's much better to attempt this with a gun with removable chokes. You can always just replace the chokes if it doesn't work to suit you.
I have also found that some guns with just one barrel can have the Up/Down problems. I can live with a 60/40 pattern, but I had Benelli SBE that threw a 90/10 pattern with field loads, and I had to correct that. I think a shotgun oughta shoot true according to the front bead, and it is a flaw in the gun if it won't. A gun with one barrel that has L/R issues is seriously flawed, imo.
A gun that doesn't shoot straight is one problem; one that doesn't fit the shooter for wing shooting is a very different issue. I suspect that most of the advice you will get will be about this second problem. That one isn't a flaw in the gun; it just doesn't fit a particular shooter. Good luck with it, whichever problem it is.
