While outwardly they appear the same and they both use the same bullet, the 5.56 has thicker case walls and a smaller capacity for powder. The 5.56 is the standard NATO round and guns chambered in 5.56 will shoot .223 with no problem at all. The opposite is not always true because the 5.56 will produce higher chamber pressure and it's not always safe in all guns chambered in .223. Also, you cannot use .223 reloading dies for 5.56 brass. The brass will not cycle through the die at all.
Yes it does, unless your barrel is stamped .223 .
No. They have matching dimensions, but differ in other areas, such as neck angles. .223 ammunition can be safely fired in a 5.56x45mm chamber; 5.56x45 ammunition is not recommended to be used in a .223 Remington chamber.
556 - 223 = 333
Yes there is a difference. They are physically the same size casing, but the 556 military rounds' chamber pressure is ~10,000 psi higher then 223. Military rifles generally have chambers with a different throat configuration than normal sport 223 rifles. This being said, I would not recommend shooting 556 unless your rifle was designed for the higher pressures.
556
.223 Remington can be cycled in a 5.56x45 rifle; 5.56x45 should not be cycled in a .223 Remington firearm.
Yes the mags work with both ammos. You can not tell the difference in the two by looking at them.
556 is a dual version of 555 single timer.
if it is a 223 cal, then yes
The cartridges are similar, but not identical. Differences include:Slight variations in neck diameterSlight variations in base diameter (.378 inches for the 5.56 vs. .376 inches for the .223)Variations in the neck anglePressure rating (380 MPa for the .223 vs. 430 MPa for the 5.56)Case thicknessYou can safely fire .223 rounds in a 5.56 rifle, but it is not advisable to fire 5.56 rounds in a dedicated .223 rifle.
Dimensionally similar, but they are not exactly the same. A firearm with a 5.56x45 chamber can accommodate the .223 Remington cartridge, but a firearm with a .223 Remington chamber cannot accommodate the 5.56x45 cartridge.
lighter bullet and more ammo can be carried as opposed to the 30/06 or 308