You should probably add MAN OR GUN (1958) with Macdonald Carey, Audrey Totter, James Craig, and (Boris Karloff's good buddy) James Gleason.  It's pretty standard stuff, except for the strong inference that there's something magical about the gun Carey wears.  With it, he seems able to handle just about anybody, which surprises even him.  Soon other folks want to get their hands on that mystical 6-shooter.  The source of the 'magic' is never made clear, but it's pretty evident that either the gun really does have special powers, or else Carey is the luckiest gunslinger in history.