I recently purchased a new Mossberg 930SPX and had the barrel threaded for a choke tube. Before I had it threaded it shot right on with the rear ghost ring site centered, Now that it has a choke tube its shooting way to the right @ 50 yards with slugs. maybe 20'' or so. Im able to zero it but the rear site has to be screwed all of the way to the left and I have to shoulder the gun in an unatural position to line up the sites. I have tried two different choke tubes and it doesnt correct the problem or change the POI at all. What might be my next option to get this thing to shoot a little straighter? Thanks, Jon