NATO-north Atlantic treaty organisation
it's comparable to a 7.62 NATO round, just a little bit longer.
430 MPa (62,366 psi) for NATO standard 5.56 ammunition. This is what is required of all NATO test barrels, which are measured at the mouth of the casing.
5.56x45mm NATO or .223 Remington. They are dimensionally similar rounds, but they are not the same. Some AR-15 rifles have smaller throats than others. If it is too small, you'll only be able to fire .223 Remington ammunition in the firearm, as the area of the throat will be too small to accommodate the higher pressures generated by firing 5.56 NATO ammunition. If the throat is reamed properly, you should be able to fire both types of ammunition in the weapon. There's no way to tell just by looking. If you try to fire 5.56 NATO ammunition in your AR and the primer pops out of the spent casing (in a best case scenario), get a 5.56 reamer (they're around $240). The reamer will widen the throat to accommodate the hotter 5.56 NATO ammunition.
POSSIBLY- and this is a stab in the dark- 7.62 NATO- similar to the civilian .308 Winchester. RG is a headstamo used by the Radway Green ammunition plant in Britain. In 1950, the standard rifle used the 7.62 NATO cartridge. Again, just a guess.
None to really speak of. They are, for the most part, one and the same. The 9mm NATO is merely a variant of the 9mm Luger loaded for military specifications.
It's primarily intended to use the NATO standard 62 grain 5.56x45 cartridge.
Without question, the .22.
The AR-15 typically uses .223 Remington or 5.56x45mm NATO ammunition. These cartridges are similar but not identical; the 5.56 NATO is loaded to higher pressures. The choice of ammunition can affect the rifle's performance, accuracy, and recoil. Other calibers can also be used with the appropriate upper receiver conversions.
5.56x45 is the ammunition originally developed for the M16 rifle. Many people mistakenly claim it is the same as .223 Remington ammunition, although this is not true - while the dimensions are similar, neck angles and other measurements differ between the two cartridges. In the late 1970s, after the US had announced that troops stationed in Europe would be equipped with M16 rifles, NATO sought a cartridge to make standard amongst their forces, in order for there to be cross compatability between NATO military forces. The weight of the 5.56x45 projectile was increased from 55 to 62 grains.
From the Ruger website: What type of ammunition should I use in my Ruger 9mm pistol? The Ruger 9mm pistols are chambered for the 9x19mm NATO Parabellum (9mm Luger) cartridge, compatible with the U.S. and foreign military or commercial 9x19mm loads manufactured in accordance with NATO, U.S., SAAMI, or CIP standards, including high-velocity, subsonic, tracer, hollow point, ammunition loaded in aluminum, steel, or brass cartridge cases, +P and +P+ ammunition.
From the Ruger website: What type of ammunition should I use in my Ruger 9mm pistol? The Ruger 9mm pistols are chambered for the 9x19mm NATO Parabellum (9mm Luger) cartridge, compatible with the U.S. and foreign military or commercial 9x19mm loads manufactured in accordance with NATO, U.S., SAAMI, or CIP standards, including high-velocity, subsonic, tracer, hollow point, ammunition loaded in aluminum, steel, or brass cartridge cases, +P and +P+ ammunition.
When speaking of ammunition it is imperative to be precise with your numbers. The .308 Winchester is interchangable with the 7.62 NATO military round