.223/4 Cal
.223 Remington and 5.56×45 mm
.223 Remington (.223) and 5.56x45mm (5.56 NATO) calibers are very similar in size. 5.56 NATO rounds have more pressure than .223, so it is dangerous to fire 5.56 NATO ammo in a .223 rifle. In some cases, you may be able to fire .223 ammo in a 5.56 NATO gun, although you should always check the specific recommendations in your firearm’s owner’s manual. This caliber is common for AR-15-style-rifles and its smaller size results in a light recoil.