Joseph Asbury was working in the Birmingham gun trade fron around 1890 up until the 1930's, possibly as late as the beginning of the last war circa 1939. I have a Tolley 2" chamber 12 bore made by Skimmin & Wood who owned the Tolley name and also a Jeffery 16 bore with the JA stamp on the barrels.
Raimy, I can help with the decimal (which should really be centimal) currency conversion from pounds shillings and pence as I was born pre the currency change. 12 pence to the shilling and 20 shillings to the pound therefore there are 240 pennies to the pound. A shilling is the equivalent to 5 new pence. Then to complicate things you may fine some old guns priced in Guineas; a guinea is £1 and 1 shilling or £1.05p. A florin is 2 shillings (10p) a crown five shillings (25p) and half a crown 2 shillings and six pence (12 1/2p) half pence pieces have now been dropped.
Most measurments are the same but I was also taught to work in rods, poles, perches and furlongs. Weights are the same except when weighing pigs which which are weighed in scores which are units of 20 pounds. The kids today have it easy but still can't do it without pocket calculators. Any conversions and I will happily oblige. Lagopus.....