In my experience, any percussion or flint gun that is marked "London Twist," "London," "Stub Twist," or variations is going to probably be Belgium or maybe Birmingham made. I have never worked on a quality London gun that lacked the maker's name and address on the rib or barrels. The same goes for Birmingham guns.
Belgium seems a good bet. Not having previously looked at British sporting gun production pre/c.1800, I hadn't appreciated how much Liège dominated twist barrel production. Having now read this: "By 1700, Liege was producing Twist barrels, and Crolle Damascus by about 1750. After Gen. Napoleon Bonaparte’s expedition against the Mameluks in Egypt and Ottomans in Syria 1798-1799, production of Damascus barrels in St. Etienne and Liege was markedly expanded. [1798 - William Dupein obtains a British patent for a twist gun barrel of iron and steel.] J. Jones was granted a British patent in 1806 for a method of making barrels from scelps or strips coiled around a mandrel and by 1817 Rigby of Dublin was producing Damascus barrels. “Damascus iron” was manufactured in Birmingham by Wiswould and Adams by about 1820 and Charles Lancaster supplied Purdey (and others) c.1811-1826 before establishing his own gun making company. [https://sites.google.com/a/damascusknowledge.com/www/home] I am left feeling that, to equip a gun with "stubs twist" barrels c.1807-1811, Mr. Cutler of Birmingham would in all probability have had to obtain these from Liège.
The proof is in the proof marks.
And there's the rub: I'm not readily finding information on proof-mark rules/conventions pre/c.1800. Most of my books choose to start at 1850 (presumably for good reason!) A nice set of Liège, Birmingham or London stamps would make everything much clearer. Instead, all I have is the enigmatic "ISH".
