The general rule is that shorter, lighter barrels are quicker to get on target and are better for quick short range shooting such as bobwhite, woodcock and forest grouse.

Longer heavier barrels provide a little more precise pointing and help smooth your swing. They tend to be better for waterfowl, dove, pheasants, prairie grouse and sporting clays.

Most people compromise and go with 26 or 28' in a 20ga O/U. Those will work for both, just see what feels best to you.