The cylinder choke might perform better than the modified choke at 20 yards. Tighter chokes deform buckshot coming out of the barrel, causing a few of the shot to go off the target. I would say you will get 6 of the 9, #00 buckshot in a pizza box at 20 yards with 2 3/4" shell. There are 15, #00 pellets in a 3" Winchester Super shell. You really need to find your own pizza box and try it on your own.