This how to video shows you how to get the optimal shotgun choke. This refers to the last 2 to 4 inches at the end of the barrel. Cylinder chokes are the most open choke with the least amount of constriction. This good up to 20 yards. This is good because the target is about 12 yards away. A skeet choke is good for about 25 yards. An improved cylinder is useful for about 30 yards. A modified choke is good for Dove hunters, which is useful for about 35 yards. A full choke is useful for about 40 yards. Remember, these are guides and not set in stone. A cylinder choke has a nice pattern at a closer range, but at a farther range the pattern is much more spread out. A full choke at 30 yards has a good pattern, but at a closer range you have little room for error. This video offers great information and examples about these chokes.