It's a style of print that is typically used to give the impression of any typical "wild west" ad. I doubt that ads from the 1960's were used as inspiration, but anything is possible.
Will freely admit I'm pretty ignorant around gun culture, there are some shooting clubs in the UK but it's not a common pastime here. Though I did go to a range last time I visited USA, it was a blast (heh). Shot a .22, a glock, and an absolute beast dirty Harry magnum thing. Heck of a kick. "Group your shots", fucker I'm not grouping shit with this kickback!