The barrel has an attached underlug with a radius machined in the underlug. This radius matches up to a hinge pin that is .375 diameter. The forend attaches to the barrel and prevents the barrel from falling off when the barrel is tipped forward to access the round in the barrel chamber. On the breech end of the barrel their is a latch on the receiver, and each barrel has a latch shelf that holds the barrel to the breech face when in the "closed" position.