Magazines for New Bushmaster .450 Caliber. While the new Bushmaster .450 utilizes a standard 20 Round AR Type Magazine Box the similarity ends there. A blue single stack follower (same as used in high power competition to load extra long bullets single shot) is installed above the anti-tilt type follower to facilitate feeding the large diameter .450 Bushmaster. A special magazine spring is utilized and cartridges are single stacked to yield a full capacity of 4 or 9 rounds. As this .450 cartridge is too wide to fit through the feedlips in the conventional .223 manner this magazine must be loaded by sliding the cartridge under the feedlips.