I would check the shells first. That being said, is that even being a shotgun, it will have its likes and dislikes of ammo. Put it on a solid rest, sandbags, heavy jacket/blanket etc.. and shoot at 40yds a paper target. Take a 4" circle and make that your aiming point. Shoot several loads, new sheet of paper each time. Look to see how it is performing. If the loads are consistently holding high, try another choke tube and see what happens. Are you keeping your head to the stock when you shoot? Some people lift their head to see what is happening. Have someone watch you or video yourself and see. I have had many young students for trapshooting lift their head and miss the bird or shoot the leading edge of the bird. I get them to keep their head down, broken bird.