The National Firearms (NFA) Act of 1934 required the registration and taxation of  weapons such as machineguns, silencers, short barrel rifles and shotguns, destructive devices and AOW.

Find more information here direct from BATFE site:

http://www.cs.cmu.edu/afs/cs.cmu.edu/user/wbardwel/public/nfalist/nfa_faq.txt

Valuable information can be found also here:

https://www.atf.gov/firearms/statelaws/26thedition/index.htm

http://www.cs.cmu.edu/afs/cs.cmu.edu/user/wbardwel/public/nfalist/semi_auto_faq.txt

http://www.nraila.org/GunLaws/Default.aspx

http://www.gunowners.org/

https://www.atf.gov/firearms/ffrrg/index.htm

https://www.atf.gov/pub/threat/secure2.htm