When patterning your shotgun, find out its maximum lethal range — the distance at which the gun puts at least 100 pellets in a 10-inch circle. If your gun puts 110 pellets in the circle at 40 steps but only 90 at 50, consider 40 your maximum range.
Don’t push it when you’re in the field, either. If a bird hangs up at 50, let him walk away, and hunt him another day.