That firearm definition was recently updated to say that only guns firing a projectile with a muzzle energy of over 1 joule need to be licensed - so pea shooters and some airsoft guns are not required to be licensed. Pneumatic guns would obviously have a much higher muzzle energy than 1 joule and would need a license.
I don't think anybody is 100% black-and-white clear on the subject of band guns - mechanically speaking they aren't much different from bows, which will fire a projectile with a muzzle energy of greater than 1 joule but which require no license.
It's a bit of a tricky spot though as it's basically open to the interpretation of whatever Gardai you're dealing with on a particular day and unfortunately if you get one on a bad day you could wind up having to surrender your gear until things can be cleared up (which would most likely take a looooonnnnnnng time!)
