ATF rule 2004-5
" ATF and its predecessor agency, the Internal Revenue Service (IRS), have historically held that the original, crank-operated Gatling Gun, and replicas thereof, are not automatic firearms or machineguns as defined. See Rev. Rul. 55-528, 1955-2 C.B. 482. The original Gatling Gun is a rapid-firing, hand-operated weapon. The rate of fire is regulated by the rapidity of the hand cranking movement, manually controlled by the operator. It is not a "machinegun" as that term is defined in 26 U.S.C. 5845(b) because it is not a weapon that fires automatically."
No hand crank, instant felon. This is why that funky little crank that clamps on your trigger guard is ok with the ATF, although many states such as Iowa have banned that even.