hand stamped bnz 4 on bsw receiver find at pawn shop

[FNG]

Greetings!

I just found this at a pawn shop but I coulnd't bring it home since the Firearm system here in the states is back logged!

I have never seen a hand stamped bnz on a bsw receiver. I bought it since it was only 200 bucks. I 'll put it in a stock and bring it back to somewhat what it was. A good thing the barrel was not not cut. Anyone tell me anything else about it, When I first looked at it I looked at the bnz and thought someone added it, Was it added by slave labour?

Any information would be nice, thank you