It's mildly ironic this subject should come up. My "magnum opus" is (tentatively) titled "The Ketland Family & the Anglo-American Gun Trade, 1790-1830." It is a project I've been working on sporadically for years but in the past six or eight have gathered a very large amount of heretofore unknown material. The basic premise is that we have a very distorted notion of American gunmaking prior to the Civil War. Not that guns weren't made here - of course they were but, in general, the vast majority of the guns used here were imported whole and of those that can be considered "American made"... virtually all have some imported components, mainly the locks but also the cast brass mounts.
Could a black smith make gun fittings? Certainly, but aside from a few places in the South, this almost never happened. Americans did make gun locks - but only in the national armories and under contract to the federal government. The entire contract system of arms procurement, starting in the 1790s, was a government subsidized attempt to secure the supply of arms exclusive of the need to import them. It succeeded to some extent, albeit bankrupting all but two of the contractors in the process. At the same time, a special act of Congress exempted all small arms from paying duty because the militia - which had to supply it's own arms under Militia Acts of 1799 and 1808, could not be armed from domestic sources.
To supply the civilian market, the making of gun locks was economically impossible. To begin with, the skilled labor simply didn't exist. And, by skilled labor, I don't mean that anyone, anywhere actually made an entire gun lock. The huge majority of them were made in three Black Country towns on the outskirts of Birmingham by a variety of specialists... cock founders, lock plate forgers, fitters, spring makers, pin makers etc. NONE were the product of a single hand. Americans had to import the most critical raw materials. There was no American steel to be had.
All of the contractors, and the national armories, bought all of their steel (and steel tools, like files) overseas - mostly in England but some German steel was used. This was true right up through the Civil War. I have copies of actual orders, from Springfield in the early days of the war, addressed to a famous Birmingham iron monger that not only specifies the materials but what it was to be used for.... Ramrods, Bayonets, lock parts etc...
This was also true for the early saber contractor, Nathan Starr. He bought most of his steel in England but also purchased German steel in New York. When faced with the government's demand that he provide iron scabbards for his sabers, he had his son recruit a scabbard maker in England and offer him a good job and free passage to America. This isn't to denigrate American manufactures, but they were slow in developing. When they did develop, beginning in the 1830s, progress was so astronomically fast that by the 1850s Britain were buying gunmaking machinery in America.
Which brings us to the really important American contribution to both arms making and manufacturing in general. Because we lacked the huge pool of skilled workmen, we were compelled to develop specialized machine tools. This, of course, aided us in perfecting true interchangeable parts. By 1842, the Springfield Armory was probably the most advanced manufacturing facility in the world.