An open ignition breech plug for a muzzle-loading firearm. The open ignition breech plug includes an internal body portion for removable installation into the breech end of a barrel of the muzzle-loader, and an external body portion comprising a gripping surface, a nipple for receiving an ignition source such as a percussion cap, and at least one open portion of the external body portion for external visibility of the nipple and a percussion cap mounted thereon. The nipple can be integrally formed with the external body portion or removably mounted thereto.