Funny thing was that most of these rifles were made in small town and rural outbuildings with less sophisticated equipment than today's average garage.
They had their Ferguson rifles they brought in during the Revolutionary War as a counter to the American weapons. They were, in fact, military-grade weapons to the American ‘sporter’ version: they were heavier, threw a heavier round, and far sturdier and easy to repair. All of which was laudable, and they thought that they had the superior rifle.
The problem was that while their rifle didn’t break as much and was more rugged, it required a base of skill they basically didn’t have in England (for a long time after 1815, too) and the more delicate American rifles generally outranged it by quite a large margin. Which some would argue is rather the whole point of rifles... especially ones that were employed in this role.