Here is an article on the gun with more technical details:
https://www.thefield.co.uk/reviews/gun-reviews/percy-stanburys-webley-scottexcerpt:
The Stanbury side-by-side has a special aura accentuated by the silver ovals on the butt which record his championship wins. The serial number is 95188, which suggests it was made in 1921. It weighs 7lb 71/2oz but feels lighter. It has very tightly choked (full and super-full), 30in barrels. These are unusual not just in constriction but because they have a wide, flat and tapered, file-cut rib (and are equipped with a tiny mid bead 10in from the breech). The rib is 7/16in wide to the rear, 1/4in at the muzzles.
Most unusually, the gun is equipped with a single selective trigger (the special work of Roland Bloomer), and bears Birmingham proofmarks for 1 1/4oz loads. It now shows London 70mm marks for 2006 (and has bores, somewhat enlarged from their original dimension, with proof diameters of 18.6mm and 18.7mm). With an imperial micrometer they measure .732 and .735. The semi-pistol stock is elegantly proportioned (and not the original). The measurements are 14 5/8in for length, with drop of 1 1/2in and 2 1/8in, with about 1/4in of cast at heel.
