HSM Ammunition Starline Rifle Brass Unprimed Cases 223 Rem Caliber 100 Per Bag. 223 Remington is one of the most widely used centerfire cartridges today. Tracing its roots back to the .222 Remington the .223 was designed to achieve certain ballistics for military use. The .223 Remington when in its military form is known as the 5.56x45mm NATO. The differences between the two being the pressures that they are loaded at and the chamber in the firearm itself. When loaded at .223 Remington pressures Starline's brass is safe to use in any firearm chambered for .223 or 5.56x45mm. If loaded to 5.56 pressures you need to use firearms labeled for use with 5.56mm. It can be unsafe to fire 5.56mm ammunition in firearms with a .223 Remington chamber. Specifications for Starline Brass Unprimed Cases 223 Rem Rifle Brass: Manufacturer: HSM Ammunition Gun Type: Rifle Caliber: 5.56x45mm NATO Primed: No Quantity: 100 Per Bag Fabric/Material: Brass Package Contents: Starline Brass Unprimed Cases 223 Rem Rifle Brass