Gunshot Western Library #1 was published by Page Publications c. December 1971.
This issue was recycled as Six Gun Western Library #3, presumably late 1972 (Six Gun Western Library #2 has a confirmed date c.July 1972):
Page Publications recycled the issue at least one more time, as Fighting Western Stories #33:
All three covers are illustrated by Keith Chatto.
I like how the cover images become progressively more violent. I suppose subsequent reprintings will feature brain-splattered corpses. One can only hope. His horror issues certainly knew the drill, even if the westerns lagged behind in this regard - consider the cover to Nightmare Suspense Library #3, a $0.20 cover-priced issue: