DEFINITION OF FIREARM

The relevant statute may be seen at 430 ILCS 65/1:1

http://ilga.gov/legislation/ilcs/documents/043000650K1.1.htm

A firearm refers to any device or machine designed to expel a projectile from the action of an explosion, or by the expansion of gas or the escape of gas. 

The following devices are excluded from this definition: 

• any pneumatic gun such as an air rifle, a spring gun, a paint ball gun, 
• or a B-B gun which expels a single globular projectile of .18 inch or less in diameter, or
• with a muzzle velocity of less than 700 feet per second, or
• any device used only for signaling or for safety (such as a flare gun) and which is required by either the US Coast Guard or by the Interstate Commerce Commission, or
• anything firing stud cartridges (a nail gun), explosive rivets or similar industrial ammunition; or an antique firearm (unless it is a machine-gun), or 
• something originally intended as a weapon that the Illinois Department of State Police decides that because of the date of its manufacture, its value, its design, and other features is considered as a collector's item rather than a threatening weapon.