Hate to rain on your parade but there were not so many things that REALLY worked doing what you wanted. Choke boring was the only real answer. Now as to the use of plastic shotcups.... They will work but you want to use one that you can custom cut the slits with..like some of the steel shot wads. Yes you can use them with lead and slit them only about half way. Try different cuts to see how much you really need. There are also some teflon wraps (house wrap stuff) you can use. I tried paper cups and foil cups and combined them with a little fine cornmeal..helped a bit. Aluminum foil cups w/cornmeal helped more than anything that I tried. Finally quit using that ol smokepole...Just too much trouble. I could get better killing patterns out of a 410...and about the same yardage. Steel shot shotcups worked better than anything....cut a bit more than halfway. Sometimes ya just gotta go in a direction you really didn't intend to. The best way just ain't gonna be traditional
