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 Delaware you can own the following items that are regulated the the National Firearms Act
Any Other Weapon (AOW)
Short Barreled Rifles (SBR)
In Delaware you cannot own the following NFA restricted items.
Machine Guns Silencers Destructive Devices (DD)
Short Barreled Shotguns (SBS)
Follow this link to find out more about Delaware and NFA restrictions on Class 3 Firearms