From an etymology dictionary, the meaning/origin of the word "pistol" is:
"small hand-held firearm," c.1570, from M.Fr. pistole "short firearm" (1566), of uncertain origin, sometimes said to be from Ger. Pistole, from Czech pis'tala "firearm," lit. "tube, pipe," from pisteti "to whistle," of imitative origin, related to Rus. pischal "shepherd's pipe." But earlier form pistolet (1550) is from M.Fr. pistolet "a small firearm," also "a small dagger," which may be the literal sense; though some connect this word with It. pistolese, in reference to Pistoia, town in Tuscany noted for gunsmithing.
Uncertain if that helps.
I'm always grateful to see and learn the roots of words because it's important to know where things of all sorts come from, especially words. But, in modern usage, I've heard many a knowledgeable firearms guy distinguish "pistols" from "wheel guns" in this way, so I'm still not clear whether that's correct or not, so I guess my question is, by today's common usage, is this distinction correct?