I haven't gotten a chance to do all the measurements, but it's a Henry Atkin 12 gauge boxlock ejector, with 28 1/2" barrels IM/Full chokes, and 2 1/2" chambers.
According to the maker's ledger, it was built around 1892 or 1893 for a Mr William LS O'Brien (whom I have decided, mostly without good evidence, is the William O'Brien MP who's imprisonment sparked the first Bloody Sunday of the Irish Home Rule movement). The serial number is 630.
As a point of personal interest, my 4th great grandfather was a tailor a few doors down, at 66 Jermyn Street, from the Atkin shop location (2 Jermyn St) where the gun was built.
The current barrels were built by Atkin, Grant & Lang in 1973 and were nitro proofed for 1 1/8 ounce loads. The gun originally had 28" barrels and later a 25" set, according to the ledger.
The stock has 14 1/2 inch LOP, with a small amount of cast-on. Not perfect for me, but I have at least two left eye dominant children in my brood, so I plan to leave the stock as is and learn to shoot it well until one of them is old enough to start hunting with it, which is still some years away.
