the backboreof a barrel has as much to do with the size of the shot pattern as the choke. most 21in barrel guns have a larger back bore so that they shoot the same size pattern as a 30in they are shorter in length to make them easier to manouver around in the brush that is why most bird hunters shoot spreeder wads to get a bigger pattern the size of the pattern might be 1/2in bigger from a shorter barrel but not enough to make a noticable difference. most short barreled turkey guns will shoot tighter than 30 in barrel gun because of there back bore.