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 Missouri you can own the following items that are regulated the the National Firearms Act
Short Barreled Shotguns (SBS)
Short Barreled Rifles (SBR)
Any Other Weapon (AOW)
In Missouri you cannot own the following NFA restricted items.
Destructive Devices (DD)
Follow this link to find out more about Missouri and NFA restrictions on Class 3 Firearms
NOTE: Starting 8/28/2011 you will be able to use a NFA trust to purchase NFA firearms in Missouri without the need of a C & R, FFL, or use of a Corporation or LLC.