95% of double design was worked out and perfected by our British cousins. The contributions by American gun designers could all be fit into a hat. Once you become a mature design field you change over into just duplicating what you did before. Doubles are durable goods and without new features there is little demand for new versions of guns you already own. And our forefathers were practical men who were content with one shotgun for everything and perhaps a .22 rifle and one larger deer type rifle. Perhaps just one shotgun.
In many ways the pump gun was the American shotgun that we created and then perfected. To an extent the semi auto was just an off shoot of this same line. Both of them lasted after they replaced doubles and some are still being made.
