I just measured my Star Dot ported 12ga Remington choke and it is .670 It will average 240+ in the 10"er at 40yds with the LB #6's. that's in a 21" 870 with 3" chamber. Funny thing is....it'll do about the same with the LB #5's. Killed a LOT of birds with the SD choke and #5 Federal Heavy Weight 2oz loads.