A couple I've been singing for a long time which feature plenty of gunplay are "Me and My Uncle" (written by John Phillips and covered by The Grateful Dead and John Denver and many others) and Marty Robbin's "Big Iron".

Also "I am Going to the West" (excellent versions by Jody Stecher and Kate Brislin and by Connie Dover).

"A Cowboy's Hard Times" by Bill Staines (Connie Dover did a nice cover).

"Hills of Mexico" (aka "Mexican Cowboy") my favorite version by The Renegades. Willie Watson also does it well.

My all-time favorite is probably "Sweet Betsy From Pike".

"Jack o' Diamonds", Connie Dover does a version in which she seems to have grafted "Rye Whiskey" onto "Wagoners Lad" or perhaps she found it like that.