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 Alabama you can own the following items that are regulated the the National Firearms Act
Machine Guns Silencers Short Barreled Shotguns (SBS) (After 7/5/10)
Short Barreled Rifles (SBR) (After 7/5/10)
Any Other Weapon (AOW)
Destructive Devices (DD)
In Alabama you cannot own the following NFA restricted items.
Short Barreled Shotguns (SBS) (Before 7/5/10)
Short Barreled Rifles (SBR) (Before 7/5/10)
Follow this link to find out more about Alabama and NFA restrictions on Class 3 Firearms
Updated 4/22/2010 SBR/SBR made legal in Alabama under act 2010-496 effective (After 7/5/10)