The Chitauri Laser Rifle is a special MythicAssault Rifle that can only be found in the Avengers: Endgame LTM. The weapon is similar to the Minigun where it overheats after a certain time period. It uses Energy Cells for the ammo, but is infinite. It was exclusive to the Chitauri team.
Since the ammo capacity is infinite, it is supposed to have a reload speed of 0 seconds, however that is somehow blocked.