A muzzle loading conversion system for a rifle having an upper and lower receiver. A barrel is slidingly secured to the upper receiver. A stationary bolt member is positioned within the upper receiver with a firing pin slidably received within a bolt opening. A breech plug mechanism is threadedly secured to the barrel within a barrel end section and the breech plug mechanism is adapted to receive a primer within a breech plug mechanism chamber which is in fluid communication with the bolt through opening. The breech plug mechanism is engaged with the bolt member within a breech plug member receiving chamber.