Flea Market find is this rare?

[PBI]

No it was a receiver made for Underwood by Singer Sewing Machine Company (subcontractor). When it was not used by Underwood because their contract to make the M1 Carbine ran out or finished, they sent the spares or leftovers to Winchester for use. Winchester either ground off the name Underwood or lined it out like this one and applied the serial number.
The B had already been applied by Singer to show it was one of the ones they made and the A stands for Accepted by Winchester. This is a very late rifle with very late features like L-479 slide, type 5 trigger housing, E W rotary safety and type five magazine catch marked W. It is in MINT condition and is now at home in the safe waiting for the next display. In the spirit of halloween and collecting TRICK OR TREAT! PBI