I'd say Jeff G's comment certainly applies to Winchester Model 12s where the 16-, 20-, and 28-gauges were built on the same frame. May also apply to Model 21s where the 16- and the 20-gauge were on the same frame, but I've only ever owned one. In my Fox doubles the 16- and 20-gauges are built on the same frame one of my 16-gauges is lighter then my heaviest 20-gauge