What is a class three firearm?

Class 3 is a designation that is applied to firearms dealers under the National Firearms Act. It covers the sale of weapons that are designated as "Title II" for individual possession.

Title II weapons include fully automatic machine guns, short-barreled or sawed-off shotguns, short-barreled rifles, explosive ordnance (such as rockets and grenades), large-bore firearms (greater than .50 caliber) and various accessories, such as silencers and pistol vertical grips. The exact rules of ownership vary by weapon type, but eligible Title II weapons require a Title 7 or Title 10 Federal Firearms License for possession and a Class 3 Special Occupation Tax for the right to sell them.