I just measured a 20 gauge single shot choke and it is around .040 constriction. I thought I might turkey hunt with it so I wanted to point of impact test it. I used 2&3/4 inch 1 ounce, 2.75 dram, and 7/8 ounce 2.5 dram 6s just to see where it hit. I was surprised to find either load put to 5 to 6 pellets in the kill zone at 30 yards!