I wouldn't call the Radom "less well known" as there were hundreds of thousands made and they were widely used by the German military and security forces. Likewise the G.43, which was widely issued; the G.41 (M) and G.41 (W) would probably fit the less well known category.
The FP-45 (it was called a "flare pistol" as a cover name), or "Liberator", was an idea that went nowhere, as only a very few were ever even sent to a combat area and even fewer (probably none) were ever used on an enemy. It was a great idea in fiction, though, and while "well known" in one sense, was unknown at the time, so it would qualify.
The Gyrojet and Dardick are odd, but don't fit the OP's category of military hardware.