Drew, thankyou for those extracts (and for the references to their sources), as well as for the images of the French twisted barrels - another thing I never knew of before.
A source you may already know, but which I came across today, and that others may be interested to know of, is John Holland's, A treatise on the progressive improvement & present state of the manufactures in metal
(London: Longman, Rees, Orme, Brown, and Green, 1831-34), 3 vols. [specifically] Vol 2, Ch.V "Firearms", pp.85-123. In this chapter we find the following comment on the 1813 legislation:
"In 1813, a bill was introduced into the House of Commons, the object of which was to oblige every manufacturer of firearms to mark them with his real name and place of abode. The Birmingham gun-makers took the alarm, petitioned the house against the bill, and thirty-two gun-makers instantly subscribed £100 to defray the expense of opposing it. They represented that they made the component parts of the London guns, which, in fact, were only put together and marked in the metropolis. The petitioners were successful, and soon afterwards, government authorized the gun-makers of Birmingham to erect a proof-house of their own, with wardens and a proof-master, and allowed them to stamp on their guns the ensigns of royalty. All firearms at present manufactured in Birmingham and its vicinity are subjected to the proof required by the Board of Ordnance; the expense not to exceed £1 each piece, and the neglect of proving is attended by a penalty not exceeding £20."
The same chapter contains quite detailed descriptions of barrel-making processes. I've made a PDF, which is available here
(if my link works!)
"The Birmingham workmen, in preparing the material for stub barrels, usually cut up strips of iron and steel with large shears into bits like two-inch nails. These bits are then arranged and annealed in a variety of forms by filling them compactly into a hoop or ring, in a manner similar to that which is common among the blacksmiths for using up old horseshoe nails. The hoop is then formed into a bloom in the furnace, after which it is welded and drawn out under the rollers or hammer into the strips already described. The metals, when properly mixed, exhibit a beautiful appearance when treated with an acidulated liquor, after which the barrel is finally finished.
Being finished at the welding shop, the barrel is carried to a workman whose duty is carefully to examine it, and, without heating it again, to set it perfectly straight by means of a few strokes with his hammer upon an anvil. He likewise tests its soundness by placing one end in a bucket of water and sucking with his mouth at the other end until the water fills the barrel. By this means, if there is any crack or flaw, however produced, which extends through the substance of the barrel, it is presently detected by the appearance of moisture on the outside. When this happens to be the case, the article is returned to the forger, and the fracture is closed by re-welding."