Abstract: An apparatus and system for loading a firearm magazine by loading all cartridges at once. According to embodiments of the present disclosure, a firearm magazine has a cartridge guide that can be locked such that the loading spring is locked in a compressed position. A loading strip that is preloaded with cartridges may be loaded into a magazine and slidably removed to load all cartridges at once. Upon loading the cartridges, the cartridge guide may be unlocked such that the spring may enable the cartridge guide to feed the cartridges into a chamber when engaged with a firearm.