http://www.atf.gov/firearms/faq/faq2.htm#c1
M. FIREARMS - NATIONAL FIREARMS ACT (NFA)
(M1) The types of firearms that must be registered in the National Firearm Registration and Transfer Record are defined in the NFA and in 27 CFR Part 179. What are some examples? [Back]
Some examples of the types of firearms that must be registered are:
bullet Machineguns;
bullet The frames or receivers of machineguns;
bullet Any combination of parts designed and intended for use in converting weapons into machineguns;
bullet Any part designed and intended solely and exclusively for converting a weapon into a machinegun;
bullet Any combination of parts from which a machinegun can be assembled if the parts are in the possession or under the control of a person;
bullet Silencers and any part designed and intended for fabricating a silencer;
bullet Short-barreled rifles;
bullet Short-barreled shotguns;
bullet Destructive devices; and,
bullet "Any other weapons."
A few examples of destructive devices are:
bullet Molotov cocktails;
bullet Anti-tank guns (over caliber .50);
bullet Bazookas; and,
bullet Mortars.
A few examples of "any other weapon" are:
bullet H& R Handyguns;
bullet Ithaca Auto-Burglar guns;
bullet Cane guns; and,
bullet Gadget-type firearms and "pen" guns which fire fixed ammunition.
(M2) How can an individual legally acquire NFA firearms? [Back]
Basically, there are 2 ways that an individual (who is not prohibited by Federal, state, or local law from receiving or possessing firearms) may legally acquire NFA firearms:
(1) By lawful transfer of a registered weapon from its lawful owner residing in the same state as the transferee. Obtain any forms needed from the Bureau of ATF, NFA Branch, Washington, DC 20226.
(2) By obtaining prior approvals to make NFA firearms. [27 CFR 179.84-179.87 and 179.62-179.67]
(M3) What is the tax on making an NFA firearm? [Back]
The tax is $200 for making any NFA firearm, including "any other weapon."
(M4) How is this tax paid? [Back]
A money order or check made payable to the Bureau of ATF together with the application forms are to be mailed to the Bureau of ATF, NFA Branch, Washington, DC 20226.
BUY IT, HAVE IT TRANSFERED TO YOUR CLASS III DEALER, SUBMIT FORM 4 with $200 TO ATF, WAIT FOR APPROVAL, DEALER GIVES IT TO YOU
and unlike machine guns that had to be made before around 1984, new silencers are made everyday for you to buy as a civilian