doublegunshop.com - home Forums Thread Like Summary - new toy and a ? on British proofs 10 Gauge

Hi All,
I just bought a neat 10 Gauge Hammer Gun from one of our members here and at my club. Its a Tipping & Lawdon hammer gun that is old enough to have a forend that comes off with a key rather than a latch. Its Damascus and super clean, nice engraving, nice wood with heel and toe plates and a checkered butt.
The question is the barrel flats are marked 763 with a punch BNP under a crown, a 10 in a triangle 3 1/2" 4 Tons per square inch (the square is a shape not a word and inch is ". There is also a circle with JB over an 8. The action flats have an oval with Patent No. 234 1870 above what I assume is a use or license number 1421.
I know this isn't 3 1/2 10 gauge magnum and is probably early 1870's.
I don't know how to load pics but have them....
The question is on the 3 1/2" chambers and the 4 Tons per sq in, were those normal? I have some British 2 7/8" 10's of around the same era but not marked that way?
Thanks

A few of the images of the 10 bore. Really nice: