Those patterns look promising, but, at the risk of belaboring the obvious, I think some of the usual recommendations to improve patterns are worth trying your next time out with shot. I presume you're already familiar with them, but I really think that with those short barrels, the effects will likely be significant.
The first is to lighten the wads between powder and shot, both individually and collectively. If you prefer the cushion wads rather than some other method for lube, split them and use just a 1/4" cushion - that has really made a difference in my 16ga. If you can lube with a patch or a schpritz down the bore, try just the over-powder card, or a few overshot cards. Even with the cushion, you might try substituting the multiple O/S cards for the O/P one. These collectively are less to tighten pattern than to reduce the chance of something disrupting it.
The other is to cut the powder charge back to 2/3 - 3/4 of the shot volume, or even to 1/2 if you try #5 shot. The reduction in gas pressure at the muzzle should have a noticeable affect on tightening the pattern, and the reduction in recoil should let you use more shot comfortably, adding to the pattern improvement. Obviously, you'll have to make sure the penetration is adequate for what you'll be shooting at the maximum range your pattern is usable, but I don't expect it to be a major problem at pistol distances.
I'm really interested in seeing what works for you.
Joel
