The ANCSL advertisement translated to English and converted from Metric to Imperial:
This imposing "Big Bore" double express was made by WESTLEY RICHARDS & C° Ltd in 1908 for ARMY & NAVY CS Ltd (Army & Navy Store Co-Operative Society Limited)[1] in London.
It uses the original system of Sirs William Anson & John Deeley as patented in April 1884.
The strong rocker implements a Purdey double lock closure backed by a third key lock at the headstock.
The 28” barrels, chambered for the formidable .500NE 3", tilt on a large diameter pin and retain, despite their age and the use of cordite, a very good condition and a very clean soul with well marked scratches.
Their convergence, set at 60 yards for the 570-grain bullet, is ensured by a one-piece wedge at the muzzle.
The interrupted band carries an express rise with five leaves lined with a gold thread set on a front sight combined with a moon sight under a sliding protection.
The stock, redone in a superb highly veined walnut, is 15” long and ends with a Silver's butt plate in red rubber.
The abbreviated front is locked by a Purdey pusher under a scalloped hood.
The weapon was completely restored by Alfred SCHILLING who kept the original engraving before applying his famous jaspage to the box.
The net weight of this "Big Game Double Rifle" is 11.9lbs.
Postscript: Everything looks pretty legit to me. The advert references good barrels with some scratches. Because of its age, it needs a standard load of IMR3031 to the Kynoch pressures using a traditional Woodleigh soft or Woodleigh traditional solid. Plenty enough for Elephant, Hippo, and Buffalo.