Wow, that is a hard one. Um, did you check to see if the choke was tight in the barrel after the first shot? Or did your sights move? That is very strange with a shot gun. I have no idea. Maybe you were shooting some messed up shells? Get you some low powers or another kind of shell and try it just to see if its your gun or the ammo.

If you want to keep that choke and find the "best" pattern with that certain choke and load. I would try the Win. XX and the Win. HV to see which does better. Maybe then if you still aren't happy, try the Xtended range, (if you can shoot that stuff out of your choke). Then, if you still aren't happy, go with Federal the same way.

I have a friend who has a 500 and bought a STAR DOT from wal-mart for $19 and it was pretty awesome with Winchester HV loads. I like 6''s myself, not sure if he uses 5's or 4's.