Jeffery (almost my namesake as my surname is Jeffreys) was a famous gun retailer around the turn of the 19th/20th century. All the authorities say he sourced his guns from makers in Birmingham for the most part and therefore never built in his own workshops/factory any of the guns sold with his name on. You should be able to get a repro catalogue from www.cornellpubs.com. The name survives as a gunshop to this day, albeit in the town of Guildford, south west of London. You could try Dig Hadoke at www.vintageguns.co.uk for a view on value.