I’m looking for a short story which involved an astronaut who was on the moon and fired a gun which caused the bullet to orbit and hit him on its return. I read this in the earlyish 50s.
I just read a story in the March 1928 issue of Amazing Stories in which that happens. It's called "Sub-Satellite," by Charles Cloukey (available to read online here).
In the hour of his triumph, Duseau had been killed. Consider the tremendous power of the Marvite gun. Long ago men calculated that a bullet shot from a gun with a muzzle velocity of 6,500 feet a second would, if there were no obstacles in its path, completely encircle the moon! And that is what happened! One of the bullets Duseau shot from the summit of "Mount Olympus" traveled all the way around the moon, and hit him in the back! And that, Kornfield, is what I was thinking about when I spoke of a sub-satellite.
Of course, it immediately reminded me of Bova's story, "Men of "Good Will," but this was probably forty years before Bova.