There seems to much confusion between various terms dealing with the National Firearms Act. There are Title 1 weapons and Title II weapons. Title II weapons are those covered by the NFA and which transfer ownership and possession must be approved the the ATF (Alcohol Tobacco Firearms) or more accurately the BATFE (Bureau of Alcohol Tobacco Firearms and Explosives).
Often people talk about Class 3 Firearms or Class 3 weapons. There is no such thing as a class 3 firearm or weapon. There is a class 3 term but it deals with an occupational tax that is paid in relation to an approved transfer of weapons.
Often people use Class 3 Firearms when they mean Title II firearms or those weapons restricted by the NFA.