A muzzle loading firearm has an elongated barrel defining an elongated bore, with a muzzle end and a breech end. A breech cap is removably connected the breech end of the barrel to enclose a chamber at the rear of the bore. A portion of the breech cap may be external to the barrel, which may be externally threaded. The breech cap may be entirely clear of the breech bore, and the bore may have a consistent profile from end to end. The barrel threads may be standard, multistart or interrupted. The breech cap may overlay the face of the rear end of the barrel.