The '.223 Remington caliber, and its military equivalent 5.56x45mm NATO, is a small, light low power round used primarily for military assault rifles like the M16 and M4, civilian personal defense weapons such as the AR-15, varmint hunting and medium game shooting. It is the standard cartridge used in the AR-15 and many other semi-automatic rifles.
The .223 has a wide range of bullet weights and designs, from the 40 gr. NT which has a muzzle velocity of 3500 fps. to the 77 gr. BTM which has a muzzle velocity of 2750 fps. There is even a 90 gr. VLD (very low drag) bullet for this caliber. The most common military ammunition loads are the M885 SS109 62 gr. FMJ with a penetrator and the older M193 55 gr. FMJ's. Unfortunately these loads depend on different twist rates in the rifle barrel for optimal stabilization. Older M16's used a 1:14" twist rate which suffered in accuracy below freezing. M16A1's, like most varmint hunting rifles, were switched to a 1:12" twist rate which is optimal for light bullets such as the 55 gr. M193. When the SS109 bullet was adopted a faster twist rate, 1:7" twist rate was required to stabilize the longer 62 grain bullet with its penetrator at the base of the bullet. Custom barrels also exist in twist rates of 1:10, 1:8, 1:6.5 and even 1.6 inches for use with the long heavy bullets. Gun owners are advised to check the twist rate of their firearm and match up appropriate bullet loads for optimal performance out of their weapon.
Appeal for Home Security
The 223 Remington's appeal for home security is due primarily to its use in the civilian semi-automatic AR-15 personal defense rifle and in military fully automatic assault rifles such as the M16 and M4, which in turn is due to its lighter weight and subsequent increased carrying capacity per soldier. With it long history of use by the United States Military, police and civilians; .223 ammunition supplies can be inexpensively acquired in large quantities.