well to me it looks like a hunk of metal. i was told this is a receiver? or at least a part of the receiver? i dont know much about it. unless you do and could help me figure it out. lol
you have part of a receiver. A stub.
Its worth about $10.
If you had a whole receiver, it'd be worth a lot. $15k with an approved form 1 or form 4, 10 years and $250k without.
That is a nice nose piece for a Thompson, figure $100-150, possibly more on the GB.
1928 front nose section. No way you'll ever get $900.00 for it, let alone $600.00
$100.00 on GB.
It's a piece of a receiver. It's a paperweight right now.
You don't have a receiver, and if you did, it would be illegal contraband.
What you have is the front 10-15% or so of a Thompson receiver, right where the barrel screws in. It was cut off of the rest of the receiver when the gun was "de-milled". It's worthless to anyone except someone with an SOT who is doing a reweld job who can't use the chunk that came with the parts kit they bought. Good luck with that.

The Sportsmans Guide was selling three cut 1928 Thompson receivers (including the piece you have) for about $100.00 a couple of years ago.