Difference between .223 and 556 Nato - The HuntingPA.com Outdoor Community
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post #1 of 4 (permalink) Old 09-17-2012, 05:08 PM Thread Starter
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Difference between .223 and 556 Nato

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Whats the difference between a .223 and a 556 NATO round ?

whats the difference between a .223 and a 556 NATO round?
I see them grouped differently when i buy ammo, so whats the difference?
4 years ago
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Alice RN

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The shoulder of the 5.56 is slightly longer and the NATO round is usually loaded to slightly higher pressures than .223 rounds. Honestly, I have shot .223 and NATO in guns that were chambered for .223 and never had a problem. But "they" say that you could possibly damage your gun shooting the 5.56 out .223 rifles.
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5.56 Nato is a bit hotter than the commercial .223 Remington version.

There are a couple of minor dimension changes in the cases also. 5.56 tends to be a bit longer than .223.

the pressures and dimensional difference.... if your gun is marked for .223 stay away from the 5.56x45NATO ..but a gun marked 5.56 would be ok with either round.

That being said.. Mini 14's are marked .223 but seem to do well with mil spec ammo...
4 years ago
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5.56 runs hotter, loaded to higher pressures, and has thicker brass. It is advised not to fire 5.56 in .223 chmabered guns. Plenty of people do it but it runs the risk of damaging the gun and/or catastrophic failure. But you can fire .233 in 5.56 chambered guns. There will be a slight loss in accuracy due to the lower tolerances when using .233 but unless your a competition shooter or care about that .2 inches at 150 yards then it's not a big deal.


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5.56 NATO is loaded to a higher pressure but all the bullets are hardball.

223 is the civilian designation and can be had w/ numerous bullet styles, weights, etc.
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The .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56x45mm NATO military cartridge. It is loaded with a 0.224-inch (5.7 mm) diameter, jacketed bullet, with weights ranging from 40 up to 90 grains (5.8 g), though the most common loading by far is 55 grains (3.6 g).

While the external case dimensions are very similar, the .223 Remington and 5.56x45mm differ in both maximum pressure and chamber shape. The maximum and mean pressures for some varieties of the 5.56 mm (different cartridge designations have different standards) exceed the SAAMI maximums for the .223 Remington, and the methods for measuring pressures differ between NATO and SAAMI.[2] The 5.56 mm chamber specification has also changed over time since its adoption, as the current military loading (NATO SS-109 or US M855) uses longer, heavier bullets than the original loading did. This has resulted in a lengthening of the throat in the 5.56 mm chamber. Thus, while .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, firing 5.56 mm ammunition in a .223 Remington chamber may produce pressures in excess of even the 5.56 mm specifications due to the shorter throat.[3]


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post #2 of 4 (permalink) Old 09-17-2012, 07:06 PM
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Re: Difference between .223 and 556 Nato

Yep. Basically, if you have a rifle chambered for .223 ONLY shoot .223 ammo out of it. If it is chambered for 5.56, you can shoot either.

Mine is chambered for 5.56 and I have only ever shot .223 out of it.
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post #3 of 4 (permalink) Old 09-17-2012, 09:53 PM
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Re: Difference between .223 and 556 Nato

from 6mmbr.com.....223 Remington vs. 5.56x45--Chambering and Throat Considerations
Is the .223 Remington the same as the 5.56x45? The answer is yes and no. There ARE differences between the .223 Remington as shot in civilian rifles and the 5.56x45 in military use. While the external cartridge dimensions are essentially the same, the .223 Remington is built to SAAMI specs, rated to 50,000 CUP max pressure, and normally has a shorter throat. The 5.56x45 is built to NATO specs, rated to 60,000 CUP max pressure, and has a longer throat, optimized to shoot long bullets. That said, there are various .223 Remington match chambers, including the Wylde chamber, that feature longer throats. Military 5.56x45 brass often, but not always, has thicker internal construction, and slightly less capacity than commercial .223 Rem brass.Should you be worried about shooting 5.56x45 milspec ammo in a .223 Remington? The answer really depends on your chamber. 5.56 x45 ammo is intended for chambers with longer throats. If you shoot hot 5.56x45 ammo in short-throated SAAMI-spec chambers you can encounter pressure issues. The new long-throated 'Wylde' chamber allows safe use of military ammo. Wylde chambers are quite common in Rock River guns. Other manufacturers, such as Fulton Armory, offer modified "match chambers" with extended throats that allow safe use of 5.56x45 ammo in .223 Remington rifles. Without belaboring the point, we'll repeat the official SAAMI position: "Chambers for military rifles have a different throat configuration than chambers for sporting firearms which, together with the full metal jacket of the military projectile, may account for the higher pressures which result when military ammunition is fired in a sporting chamber. SAAMI recommends that a firearm be fired only with the cartridge for which it is specifically chambered by the manufacturer."

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post #4 of 4 (permalink) Old 09-18-2012, 02:26 PM
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Re: Difference between .223 and 556 Nato

i think number of grains(gun powder) thats why some 556 ammo is so cheap
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