There are several type of Class 3 items that are restricted by the National Firearms Act.
Each state can impose additional restrictions on the sale, purchase, and transfer of class 3 firearms in addition to the compliance that is required with the national Firearms Act.
In Wisconsin you can own the following items that are regulated the the National Firearms Act
Machine Guns *In Wisconsin you cannot own the following NFA restricted items.except for scientific purpose, or the possession of a machine gun other than one adapted to use pistol cartridges for a purpose manifestly not aggressive or offensive (see 941.27(2) Exceptions to 941.25 and 941.26)
Any Other Weapon (AOW)
Destructive Devices (DD)
Short Barreled Shotguns (SBS)
Short Barreled Rifles (SBR)
Follow this link to find out more about Wisconsin and NFA restrictions on Class 3 Firearms