If you need more choke, powder the gun then seat a O/P wad, then seat a fiber wad with a hole punched through the center, then a O/P wad, then shot, and a thin Over shot wad. The bigger the hole in the wad the tighter the choke effect, to a point. For a more open choke, use an X card, which divides the shot charge into four vertical sections. Do not use a thicker O/S wad than necessary, as this will cause a 'hole' in your pattern.