A rapid-fire automatic gun is provided with a first maga- tine (6a, 6b) for a lesser number of rounds, and a second magazine (7) for a greater number of rounds. These magazines include first and second round advancement members (15, 16, 17; 21, 25, 26), respectively. The first of these round advancement means are controlled by the automatic gun proper, such that a round advancement speed depending upon the firing rate of the gun prevails in the first magazine. The second round advancement means (21, 25, 26) are drivable by drive means which realize a maximum round advancement speed in the second magazine which is considerably less, for example of the order of magnitude of 100 rounds per minute, than the maximum round advancement speed in the first magazine. Transfer means transferring rounds from the second magazine to the first magazine realize gap formation in the row of rounds in the first magazine when there is a difference in the advancement speeds of the first and the second magazines, these being successively filled during and after firing.