User blog comment:Menara/The Mark of Athena Character Art Revealed!/@comment-4430596-20120904003141/@comment-3146930-20120904030655

Simple, guns need to be reloaded and Celestial Bronze/Imperial Gold isn't unlimited. Meaning you would eventually run out of the material to make bullets with while the sword in the corner of the room is ready to go. I mean even the Apollo cabin and Hunter will retrieve their arrows after a battle, but finding a bullet would be much harder. However, gods like Ares tend to have guns and there was a shotgun in the weapons shed at Camp Half-Blood.