Army Inspectors

US Army officers served as inspectors, stationed at the Colt factory. They were equipped with sets of gauges, plugs and measuring instruments. Somewhere during manufacture, revolvers intended for the government got a “US” stamped on the frame’s left side under the cylinder. That did not automatically mean the Colt was accepted. When one was deemed good enough the inspectors stamped a “cartouche” containing their initials into the left side of the walnut grip.

There exist early Colt .45’s with the “US” stamp but with nickel-plated finish and ivory grips (one piece also). The story there is inspectors were very finicky about what they stamped their initials into and Colt considered some of their rejections as viable sales items. Thus they were finished and fitted with grips and then sold on the civilian market.