HSM Ammunition Starline Rifle Brass Unprimed Cases 450 Bushmaster Caliber 50 Per Bag. As with most AR cartridge conversions it only requires swapping out the upper receiver. With the introduction of some new bolt action rifles in this caliber and many states changing game laws allowing straightwall cartridges for deer hunting the .450 Bushmaster is enjoying a surge in popularity. Ruger now offers their American Ranch and Gunsite Scout bolt action rifles chambered in the .450 Bushmaster caliber. This cartridge utilizes the common .452" diameter bullet reloaders can use bullet weights anywhere from 160-350+ grains. Specifications for Starline Brass Unprimed Cases Rifle 450 Bushmaster: Manufacturer: HSM Ammunition Gun Type: Rifle Caliber: .450 Bushmaster Primed: No Quantity: 50 Fabric/Material: Brass Package Contents: Starline Brass Unprimed Cases Rifle 450 Bushmaster