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 Iowa you can own the following items that are regulated the the National Firearms Act
Any Other Weapon (AOW)
Destructive Devices (DD)
Short Barreled Shotguns (SBS)
Short Barreled Rifles (SBR)
In Iowa you cannot own the following NFA restricted items.
Although Title II firearms are permitted in the state their ownership is severely limited to the following circumstances.
1. Any peace officer.
2. Any member of the armed forces of the United States or of the national guard.
3. Any person in the service of the United States.
4. A correctional officer, serving in an institution under the authority of the Iowa department of corrections.
5. Any person who under the laws of this state
and the United States, is lawfully engaged in the business of supplying those authorized to possess such devices.
6. Any person, firm or corporation who under the laws of this state and the United States is lawfully engaged in the improvement, invention or manufacture of firearms.
7. Any museum or similar place which possesses, solely as relics, offensive weapons which are rendered permanently unfit for use.
8. A resident of this state who possesses an offensive weapon which is a curio or relic firearm under the federal Firearms Act, 18 U.S.C. ch. 44,solely for use in the official functions of a historical reenactment organization of which the person is a member, if the offensive weapon has been permanently rendered unfit for the firing of live ammunition. The offensive weapon may, however, be adapted for the firing of blank ammunition.
9. A nonresident who possesses an offensive weapon which is a curio or relic firearm under the federal Firearms Act, 18 U.S.C. ch. 44, solely for use in official functions in this state of a historical reenactment organization of which the person is a member, if the offensive weapon is legally possessed by the person in the person's state of residence and the offensive weapon is at all times while in this state rendered incapable of firing live ammunition. A nonresident who possesses an offensive weapon under this subsection while in this state shall not have in the person's possession live ammunition. The offensive weapon may, however, be adapted for the firing of blank ammunition.
Follow this link to find out more about Iowa and NFA restrictions on Class 3 Firearms