That gun dates to the time when machineguns could be manufactured or converted from semi-autos for sale to individuals. It looks like it was converted to selective fire in Germany (Dauer = full auto, Einzel = semi-auto, Sicher = safe) then imported by Action Arms. It should have been sold on a Form 4 as a registered machinegun. If it is now semi-auto only, someone may have messed with it believing that it would be legal if it were converted to semi. If my surmise is correct, BATFE should have a record of the gun, and it may in fact be registered and legal.