I am a firm believer in what they call "wad lock" choke tubes. This design slows the wad down thru friction, so that it separates the wad from the pellets and shortens your shot string. Don't forget that whatever patterns you shoot on a stationary target is only a 2 dimensional representation of a 3D event. Bottom line, shorter shot string means birds are hit harder due to more pellet strikes. Granted, you don't want a pattern with holes in it, but even an evenly spaced pattern on paper could mean big holes in the shot string. Try shooting over water some time, or pay attention when you water swat a cripple. It can be amazing to see how far the string stretches. A wad lock choke throws a much shorter string of shot, and gives you a better chance of either a solid hit or clean miss. I prefer Wad Wizard tubes, but Patternmaster and probably some others provide the same effect.