Obviously, condition and price are key to value. So advice to have the gun inspected by a competent gunsmith is important. If that is not allowed, pass.
Re Joseph Lang, he was an important innovator in the 1800's, in fact the first London gunmaker to build and sell breachloading guns. They were also the makers of the Vena Contracta, which may well be one of the worst ideas in game gun design, ever.
I can't find any reference to suggest Lang made anything but best guns, but as y'all know, the records are not complete for any of the old firms, so who knows?
If you want to see a good example, take a look here:
http://www.gunsinternational.com/JOSEPH-LANG-SXS-SLE-12-GA.cfm?gun_id=100514342http://www.gunsinternational.com/JOSEPH-LANG-SXS-SLE-12-GA.cfm?gun_id=100514342
It was built in 1906 and shoots beautifully. I know because it was my gun.....
