Common misconception furthered by Doom's naming of it's weapons (and I think a couple of other games). The Doom's "chaingun" was a Gatling gun (of unknown model). Technically, the term "minigun" comes from what the M134 was nicknamed. People have just applied it to all Gatling guns for some reason.
" This seems weird to me. Let me see if I got this right: Call of Duty 4 includes a Desert Eagle, which means Gun, Pistol and Desert Eagle should be attached? Why not add some more categories while we're at it? Weapon -> Gun -> One-handed Gun -> Pistol -> Desert Eagle -> Golden Desert Eagle. "
Well, that's not what it was originally for I think but its sort of evolved into that I guess. Its got other uses. For instance, for games that have no particular gun but do in fact have one, like Asteroids. the ships have guns but there is no name for them.... unless there is a pea-shooter concept page (I'm actually not sure)
In any case, weapon would not be a object. It's vague enough where I'd consider it a concept maybe. As for "one-handed gun" I'd say that it is a bit of a stretch to say that there a point to that one. That is like saying "yellow fruit" (unless there is a specifically named object in a game that goes by "Yellow Fruit") should be an object. "Adjective + Noun" does not make a object page.
So Maybe: Weapon(concept) > Gun > Pistol > Desert Eagle > Golden Desert Eagle
Oh and for your first question, IMHO, I'd say yes, they probably should if they are not.
It essentially works as a category for the guns. I just went through the entirety of the objects database checking the guns I found and was making sure they were connected to this page. Yay for OCPD! So if you went to the objects page of the guns page you should find most if not all the guns in GB.