Boresighting a shotgun is not the same as boresighting a rifle. It only gets you close. The pattern your gun throws will be different with different loads and even brands of shells, after boresightng experiment with which shell/manufacturer gives you the best pattern in your gun, then sight that pattern in with your red dot scope. Shoot only that brand/load shell, another brand/load will probably shoot differently. At least this is true out of my cheap old Mossberg 500.