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Just logged in for the first time. I posted a pic of my mis-stamped M77 Tanger on the Facebook page. Stamp says its a 30-40 Krag. Of course we all know Ruger didn't chamber the 77 in Krag but sure enough the stamp is right there where it is supposed to be.

Bolt face is .473"
Barrel is .257
Box says 257

Any value to a factory mistake?

Welcome aboard. Any mismarked Ruger is of interest to collectors. That is sure an interesting M77, marked with a No. 3 caliber. Maybe some M77 collectors will tune in and let you know how interested they might be.
FT44