I'm thinking primarily pumps here. I've read elsewhere that a shotgun built with a frame specific to the gauge fired is much handier.
For example, when asked why use a 16ga when a 12 is so common and close, 16ga fans explain that the real benefits are gained with a 16ga on a 16ga frame.
Well that led me to wonder which shotguns out there really were sized for the gauge of shell they fired. From my engineering perspective, making a different frame for a 12 and 16ga, as close as they are, doesn't make a whole lot of sense, though I can understand the advantages, however small they may be.
20ga, on the other hand, well it seems pretty dang cheap to make a 20ga with the exact same frame as a 12ga. When looking at the array of shotguns lately, it seemed as though Winchester does that with the model 1300. Is that the case? And are there other shotguns that have the 12 and 20ga built on the same frame?