I've got a Colt AR-15A2 conversion with manufacturer's markings that are only visible when you remove the pistol grip. Also remove the magwell and look under there. Strip the gun and look in every conceivable place for manufacturer's markings. When it comes to NFA, I've learned to never say never. This doesn't mean there aren't variations out there. I've observed at least five different DLO marking locations on Sterling tubes ranging from bill board size to very tiny, but all have been on the left or right side of the tube. The Wilson 'Stenchester' I owned had the serial number in a conspicuous location on the tube as have other Wilson Arms, Brunswick, GA examples I've seen. So weird to me - I guess the magwell is the serial numbered, registered part? Nothing on the tube or what I would call the trigger housing / receiver. On the bottom is another series of numbers. There is a very faint series of number above 'STEN Mk II' on the top. Yes, 'top' or 'bottom' is a better way to describe it. M/78 is the manufacturer’s code for Elkinton & Co of Birmingham. You might have to strip the paint off to find it. It will be either on the top or bottom of the mag well.
