The .50 BMG is one of the largest rifle cartridges in common use—designed for anti-materiel work. A derringer is a small, concealable handgun. Combining them is absurdist engineering—creating a weapon that's simultaneously designed for penetrating heavy armor and fitting in a palm. It's logistically impossible and therefore perfect apocrypha.

Weapons designer Marcus Thompson, teaching military history at a university in 2008, found this fact referenced among students: "April 2008, someone asked if such a thing could theoretically exist. We discussed the engineering impossibilities. But the fact had captured people's imagination because it conflates scale—the idea that Chuck could miniaturize extreme power."

The humor works because it's technically nonsensical yet poetically appealing. A .50 BMG derringer would be impossibly powerful and completely unusable. The fact has become a way to discuss the fantasy of having maximum capability in minimum space. In engineering and military communities, it resurfaces when discussing hypothetical impossible weapons.