NFA
The National Firearms Act of 1934 — regulates suppressors, short-barreled rifles and shotguns, machine guns, and other items.
The NFA (1934) imposes federal registration, a $200 tax stamp, and a multi-month ATF approval process on certain items: suppressors, short-barreled rifles (SBRs), short-barreled shotguns (SBSs), machine guns, and “any other weapons” (AOWs). NFA items are legal to own in most states; the process and paperwork are the friction.