Don’t want to assume anything so here goes. These little guns while are functional they really aren’t made to be fired. They are made of a soft metal and no liner, within a few shots any rifling is gone.
Single shot spur trigger derringer chambered in .22 short, manufactured circa 1960's-1970's. Butler produced these derringers for Colt between 1959-1963. When Colt dropped the line Butler continued production and stamped their own name on the guns.