firearm nerd

1. Someone who knows a lot about firearms and likes to study them. This could apply to either historical firearms (like the Lee Enfield and the tommygun), or modern firearms (i.e. Glock, USP, MP5, the M16 family), or a combination thereof

Steve is a firearm nerd. He could name you thirty different automatic firearms in his sleep in addition to their clip size, fire rate, and ammunition type