We've seen the "1A", "1B" "F" & "I" stamps, but the "B"?
 

Josh Loewensteiner has listed on GI an A-1 Special 2-bbl. set with a "B" stamped between the barrel lugs on both sets of barrels. This area or on the forend lug is usually reserved for 1 or 2 to indicate the set of barrels. The forend lug is not shown to see if it's stamped.

I wonder what the "B" indicates? This qualifies as a never-have-been-seen-before, at least to myself, have you?

That is a real low SN and may be from a prototype?

This seems like an odd ball. Meriden conn, Vulcan Steel barrel marking on PR barrel? Non A1 grade case. Angelo Bee engraving? Doesn't look like his style. I'd have to see the paper work. Looks like an A1 in the white upgrade.

https://www.gunsinternational.com/gu...n_id=102674101

What's the B?
 

Why not just ask Josh?

Vulcan Steel marking? If you mean the pw mark that's a Winchester proof mark. I looked at the GI pictures and I see what you mean, it's on the rib. Very strange.

Ad mentions two different engravers. Might be a composed 2 barrel set with a reworke seconc set of barrels from a V?

Both barrels are PR barrels according to the pictures of the barrel flats. It seems like the ribs were replaced with Meriden ribs. Lots of work.

Another possibility is that the barrels were sent to Japan to be fitted to an A1 receiver, marked in the Reproduction fashion and returned. Since the top rib view is only of one of the barrels, it's only speculation.

I did, but he doesn't know.

In regards to the barrel legend . . . the gun is custom engraved, why couldn't the gun's original rib legend have been struck off and either re-roll stamped or hand engraved? Why the "Vulcan Steel" -- only the owner that commissioned the work knows for sure. (Again, another scenario of speculation, mystery and intrigue).

Circling back to my original question . . . what does that "B" indicate?

Edgar's explanation is a very real possibility. Sorry, can't offer anything on the "B".