Who built 10 gauge shotguns?
Many companies built them in both black and smokeless powder variants. Remington, Ithaca, H&H, Greener, Wadsworth, etc..
Conventional shotguns run from 10 gauge (very big) to a .410 (smallest). The most common are 12 and 20 gauges, a little less common are the 16 gauge and .410 (.410 = 67 gauge). Some of the less common gauges are 32, 28, 24, and 10 gauge. There are also monster 'punt' guns usually 6 or 8 gauge mounted to a boat. The smaller the gauge number, the bigger the gun.