Read a short story back in maybe the seventies or eighties where a time traveler served as inspiration for the legend of Thor. Seems that he shot someone with his gun and since it never left his hand the natives thought that he struck someone at a distance and it returned to him. He had, upon his return, the word "Mjolnir" inscribed on the gun. That is literally the only detail about the story that I remember.
This has been asked and answered here before. The story is called "Frost and Thunder" and was indeed written by Randall Garrett.
I think I know what happened. I remember hearing Hrotokar in the background saying: "His hammer smashed them! Killed them! And then came back to his hand!"
I can see how that illusion could come about. I hold the hammer in my hand and there is a thunderbolt and the foe falls dead—his head smashed in. And then the hammer is back in my hand. Sure.
Those folk had already shortened my name from "Teydor" to "Tey'or"; why not one syllable further?
My weapon has a name now, as Sten suggested. I looked up a man who knows Norse runes, and I had another man engrave those runes on my pistol, on the right, just above the trigger.
The engraving says: Mjolnir.