Slug guns must be zeroed (sighted-in) at a distance where the slug will impact the target while still in the supersonic phase of its flight. Most slugs become subsonic, travelling less than 1220 feet per second, slightly beyond a muzzle distance of 50 yards, thus making 50 yards the ideal zeroing distance. Zeroing at 50 yards also cuts down, by approximately 60%, the chance of adjusting Windage error into your scope setting.