Browsing one of the auction sites, I came across a strange (to me anyway) BSA barreled action. It looks like a No 1 but is only marked BSA Co on the right butt socket which I presume makes it a commercial unt. The S/N on the barrel matched a number on the top of the receiver that would be covered when the bolt is closed.

Anyway, the barrel is marked on the left side of the chamber with "8M/M Nitro Proved" as well as what looks like a proof mark over "BM".

Why "8M/M"? Is that just a matter of rounding .303/7.7MM to the next full number or is this rifle chambered in a caliber other than .303?

Thanks.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.