War trophy paperwork from the US govt is considered 'registration'. The ATF has been known to update the registry with WW2 bringbacks that had documentation but was never formally added to the registry. A mint FG42 would sell at auction for more than $150000. So I'd look around for war trophy paperwork if you dont see any normal ATF forms for the weapon. Anything on paper from the Dept of War, Treasury, or even commanding officer might make it legal to own and worth huge bucks.
Don't do anything stupid like cut it up or surrender it to LE until you know for sure it is contraband
Next time anyone thinks they found a machinegun in their attic, definitely talk to a lawyer if you think it's worth something or not.
Possession of an unregistered or improperly registered machinegun isn't going to be a slap on the wrist charge, it's a Federal Felony with a decade in prison and $10,000 fine.
Easiest way to tell if it is a genuine FG42 is to simply work the action. The selective fire lever is on the left side of the receiver right above the trigger. If the bolt stays open in the auto fire mode it is genuine. The FG42 fired from a closed bolt when in semi-auto mode and from an open bolt when in FA. Selector is shown in the image below. If the bolt does not stay in the open position, it may be a BD42 which was the FG42 semi-auto version.
An original Nazi FG42.....a vet bring back at that. God only knows what it took to capture one .......one of the finest machine guns ever made. Our own M60 is based off it.
I wouldnt care what it'd be worth. Id hang it above the fire place. And hope for SHTF.
If Peter doesn't tell Paul, then Paul will never know. Sometimes you just gotta tell the government to kiss your ass.