A firearm includes a breech or firing chamber 101 where the cartridge is made to explode, and a mouth portion 102 adapted to cause the cartridge to pass from the magazine to the breech. The magazine is engaged to the breech and includes a plurality of chambers 21 sequentially mobile with respect to breech 101 so as to present one after another in the loading position in which a charging mechanism 7 inserts the cartridge into breech 101. Each single chamber 21 can slide independently on at least one track 22 placed on the magazine longitudinally with respect to the axis X of breech 101.