The .223 Remington cartridge containing the 55 grain full metal jacket (FMJ) projectile are by far the most widely used round for the AR-15 platform. This full metal jacket round is capable of being fired in barrels labeled as 5.56x45mm NATO, .223 Rem, and .223 Wylde. The 55 grain projectile (.224 diameter) is the ideal weight for a wide range of barrel twist rates to include the 1-in-7, 1-in-9, and 1-in-8.
MIXED HEADSTAMPS! Your ammunition may have a mix of 5.56 and .223 headstamps.