Oftentimes photographers pursuaded unwilling subjects by offering suitable props for the sitting. Of course a revolver and a clean service jacket and hat would be nice.
Investing in such items made good sense for a man in this businesss.

Thought of a different way, men on leave in a large town generally weren't allowed to take weapons out of camp. It spared a lot of trouble for all parties concerned, especially if soldiers intended on visiting a bar or two in the city.