Bushmaster Firearms M4 Patrolman's AR-Style Semi-Auto Tactical Rifle .223 Remington 16" Barrel (1)-10Rd Mag Right Hand A2 Front, Flip Up Rear Sights 6 Position Collapsible Synthetic Stock Black Polymer Finish

Introduced in 1964, the 223 Remington is the civilian version of the 5.56x45mm NATO cartridge. Although very similar to the 222 Remington it has a slightly longer case and a shorter neck, giving it greater powder capacity and thus higher velocity--which was necessary to meet military penetration requirements at longer range. NOTE: 223 Remington ammunition may be safely fired in any 5.56x45mm chamber, but 5.56x45mm ammunition SHOULD NOT BE USED in a 223 chamber! Standard is a 55-grain bullet at 3240 feet per second, with lighter bullets somewhat faster and heavier bullets a bit slower. The 223 is the most popular 22 centerfire today, and possiby the most popular centerfire cartridge. Ammunition choices are legion, as are choices in firearms. The 223 is an accurate cartridge ideally suited for varmint hunting out to beyond 300 yards, and with heavy-bullet loads designed for the purpose is used effectively by many deer hunters. — Craig Boddington