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 Puerto Rico you can own the following items that are regulated the the National Firearms Act
Machine Guns- Manufacturing only Silencers – Police only Short Barreled Shotguns (SBS)- Police only Short Barreled Rifles (SBR)- Police only
In Puerto Rico you cannot own the following NFA restricted items.