Class III NFA weapons ownership can be very complicated. There are not only federal laws to contend with, but state and local laws as well. That said, it is not impossible to legally own an NFA weapon.
A good place to obtain information on owning, using, maintaining and just about everything else concerning these weapons is The Small Arms Review (
http://www.smallarmsreview.com/) published by Moose Lake Publishing (Dan Shea). They also publish an ATF/NFA Handbook, which may answer many of your questions.
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