As the PM73 RAK is an open bolt submachine gun, it requires the bolt to be open and the chamber to be empty when a cartridge is being fed in, so that you do not result in a double feed that would jam the gun. Whilst you would be able to single chamber the gun by physically seating a round in the chamber, pulling the bolt back, and then dropping the bolt on the round through pulling the trigger, you cannot have a round seated in the chamber when you fire with the magazine, as the bolt would strip a cartridge from the magazine and try and push it into the already full chamber, jamming the gun. Therefore, the PM73 RAK should NOT be able to hold one extra in the chamber with a full magazine behind it as the gun would jam. You should have to eject any single rounds form the chamber to be able to attach a magazine to the RAK, and the RAK will not be chambered when the magazine is removed.