Some folks don't quite get it.....THEY'RE THE SAME THING!!!!! The dimensions of 5.56 NATO and .223 Rem rounds are the same.
Military brass is superior as it is thicker, especially in the web area. This will give you more reloads. Quit making something so ridiculously simple so freakin' difficult. It's obvious you are a newb, but this is way too much and there is a lot of info on this thread that is dead wrong. Doesn't suprise me as folks give opinions when they should keep their mouths shut. The chamber is different between the two, while the dimensions are exactly the same.
Mil brass is easy to resize. It's a .223 Rem case, not 30.06 or .308 Win. A baby could resize this stuff. The only negative is the primer pocket crimp. Two turns of an RCBS chamfering tool and it's done and it only has to be done once.
READ THIS AND UNDERSTAND....
223 Remington versus 5.56 mm NATO
These 5.56x45mm NATO cartridges are identical in appearance to .223 Remington. They are, however, not completely interchangeable.While the 5.56mm NATO and .223 Remington cartridges and chamberings are very similar, they are not identical.
Military cases are generally made from thicker brass than commercial cases; this reduces the powder capacity (an important consideration for handloaders[9]), and the NATO specification allows a higher chamber pressure. NATO EPVAT test barrels made for 5.56mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 137.9 megapascals (20,000 psi) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 megapascals (62,000 psi) for 5.56mm NATO, is reduced by SAAMI to 379.21 megapascals (55,000 psi) for .223 Remington.[10] In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56mm NATO.
The 5.56mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[11] or the ArmaLite chamber, which are designed to handle both 5.56mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56mm NATO chamber specification.
Using commercial .223 Remington cartridges in a 5.56mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade.[12] Using 5.56mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and the SAAMI recommends against the practice.[13][14] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14, but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56mm NATO ammunition.[15]
