Thanks for the latest photo 'Marksc'.

It looks to me like Springfield Armory workers missed some machine operations on your receiver, before it was heat-treated and Proofed. This could not be corrected after heat-treat.

I've never seen an unfinished receiver before. Cool!

That probably explains the absence of a serial number. It was probably 'scrapped', but, someone later made a "carbine" out of parts.

Attached - Contrasting photos of Mark's receiver and a model 1899 receiver, showing considerable difference in 'trigger pivot' area. The receivers should look identical.

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