This is another example of a late turn-off barrel pistol, which some people mistakenly call a Queen Ann. Much like your previous
post, just using a percussion cap. There can be little doubt that it is a breech loader.
Unscrewing (turning off) the barrel reveals a chamber at the breech that is easily filled with a precise amount of gunpowder. The lead ball fits in a cup on top of the powder. When screwed back on the ball fits tightly in the barrel making the wadding used in a muzzleloader unnecessary. When fired the increased pressure made possible by the tight fit added to both range and accuracy. The tight fit also made it easier to carry loaded for long periods of time than a muzzleloader.
FYI: my avatar is a rifled turn-off barrel pistol c1690.