That one's easy: an air weapon fires a projectile that isn't a 6mm plastic BB using an air pressure not greater than 12ft/lbs for rifles or 6ft/lbs for pistols; a Firearms Certificated air weapon fires same using air pressure greater than 12ft/lbs for rifles (air pistols over 6ft/lbs are Section 5 and therefore entirely illegal FAC or no FAC); airsoft guns fire exclusively 6mm plastic BBs (yes, yes, I've seen the 6mm glass BBs on AliExpress - technically it'll fire any sphere 6mm in diameter) at a power of less than one joule. 4.5mm Dan Wesson revolver? Air weapon, ergo Actual Firearm. 6mm Dan Wesson revolver? Airsoft gun, ergo Realistic Imitation Firearm. Simple as that. EDIT: Andy, if you're looking for your post, I moved it 'ere because you were asking about air weapons rather than airsoft RIFs.