From Halopedia, the Halo wiki
An ammo printer or munitions printer is an ammo-producing machine used by the Banished.
During the Installation 07 conflict, the Banished established a munitions depot on Zeta Halo called the Armory of Reckoning. By May 28, 2560, the Armory of Reckoning had only three functioning ammo printers left. When Master Chief Petty Officer John-117 stormed the Armory, he destroyed the three remaining ammo printers, effectively crippling the Armory.