Justin - thanks for that suggestion.

jOe - I think I see two sets of marks:

1. BV/BP/NP Diamond with a 20/C, 21/2" Nitro Proof 7/8 [original post-1925 marks?]

2. Crown/R [for re-proof], BNP, 20-70-950 Bar, 15.9/15/7 [post-1989 reproof marks?]

Do you see something else?

This would suggest that the barrels were honed to 15.9mm (0.625") at the same time the chambers were lengthened?

Isn't it odd that an underlever would have original proof marks post 1925 - were they still making underlevers that late?

Such a long, long time to be gone, and a short time to be there.