It should not be hard to find historical examples of American individuals making their own firearms even back to the founding.
Thousands of examples as a matter of fact. However most guns, pistols, smooth-bores and rifles were made by private gunsmiths who had the skills to hand forge locks, stocks and barrels. There were what you could call gun factories back in the 1700s, in Europe called armories where they mainly produced military muskets and trade guns for use by fur traders in contact with North American Indians.
“It should not be hard to find historical examples of American individuals making their own firearms even back to the founding.”
That is true. Even just a couple decades ago, making “potato guns” out of PVC pipe was a big thing around my neck of the woods. We’d..... argh... I mean... I’ve heard that people would take them to the large lake nearby and shoot potatoes out over the water. The method and physics of it works the same with any projectile.