More precisely, at least as I understand it, a pistol is a type of handgun (handelsavtal, handeldvapen), revolver being another. A gun, in English, is any type of firearm, including assault rifles, cannon, etc. Since we're on the subject, could we sort this terminology out a little better?
Likely, because Sweden has very stringent gun laws which require a license (I know of 2: a license for sport shooting and one for hunting) to own/use, and require highly specific storage/transport requirements (Even if you are just a collector!) The Swedish government considers it a privilege to own a firearm; not a right. As this is not the rule of law in all countries, it seems fitting (at least to me) that this is in the Politics section.
Everybody seems to think this is something specific for the Swedish tree (there was a comment about it in another thread very recently) but actually weapon was in the Politics skill in the template tree we got from Duo when we started creating the course (along with war and army) so it isn't our idea :D