"Firearm" means any device, by whatever name known, which is designed to expel a projectile or projectiles by the action of an explosion, expansion of gas or escape of gas; excluding, however: (1) any pneumatic gun, spring gun, paint ball gun, or |
| B-B gun which expels a single globular projectile not exceeding .18 inch in diameter or which has a maximum muzzle velocity of less than 700 feet per second | |
This is from the IL compiled statues available on the IL site.
Sadly, even more weirdness comes with the use of LESS THAN 700. So if its advertised as a max velocity of 700 that may break the law by 1fps. If advertised as UP TO 700fps this is likely safe by implying it cannot actually break above 700. Stupid stuff. Sorry to waste your time