The invention provides an ammunition storage box that stores and loads multiple successive rows of ammunition cartridges into firearms magazines. The box includes an interior channel and multiple openings that lead into the channel. The channel is configured to host and dispense cartridges into a firearms magazine interfaced with the box via a proximal opening, which leads into the channel. The box also includes cartridge slots, recessed into the box and convergent with the channel, configured to host cartridges. The box also includes an obstruction block configured to selectively engage within the channel and obstruct cartridges hosted within the cartridge slots from moving into the channel. The box also includes a rod, configured to slideably engage within the channel and displace obstruction blocks or cartridges within the channel out from the channel. The rod is also configured to encapsulate the cartridge slots when expanded into the chamber.