Is the bbl stamped .649 or 17; or both?. .649" is the nominal dia of a 17ga bore, but if it has the .649 mark stamped in the bbl, then I believe it would have been proofed, or re-proofed, after 1954. I could be wrong, but I thought .008" (2mm) enlargment was considered the limit before a gun was out of proof. Originally it was when it would accept the next up plug gage size(17/1-.656") to the depth of 9"s.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra