In an era where muzzleloading was the general rule, our GOTD was one of the few exceptions. The .67 caliber Pendrill flintlock had a flanged port cover on the top of its barrel that could be twisted to provide access. The loading hole was big enough to drop a round ball into, followed by blackpowder. A further benefit of the port cover was that the flanged top could also serve as a large rear sight.
Circa 1740, gunmaker J. Pendrill is known to have produced both conventional muzzleloading and breechloading arms.