Oh crap.. I think the Kentucky Rifle was War of 1812..er.. actually, that's when the term came into use. The Kentucky/Pennsylvania rifled musket prototype appeared in 1725, so it would have been deployed by rangers on the American side, but you mean British..
I do recall the unit you are mentioning, one of the sharpshooters had George Washington in his sights once, and didn't kill him because it wasn't a sporting shot.