To show the language problems you can get with descriptive terms for guns, take the direct spring propelled guns (i.e. those not using air compression) for example.
One of those fiendish anti-poacher spring guns (apologies to whoever gave me this pic - I didn't note who it was).
Vintage Airguns Gallery
..Above link posted with permission from Gareth W-B In British slang an anorak is a person who has a very strong interest in niche subjects.