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.223 Rem vs 5.56x45 NATO

hdrulz99
I'm confused - I thought that .223 Rem and 5.56x45 NATO were the same round. However, when looking in catalogs, these types are separated even under the same brand. The only difference that I can see is that the .223 Rem is a 55 grain bullet while the NATO rounds are 62 grain.

Can someone please explain this to me?
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Comments

6 comments

Date Votes
  • Colt Super
    NATO changed the bullet weight for better range and stability, as I understand it. The 5.56 NATO rounds stabilize better with the rifling twist in NATO rifles, and carry more energy downrange. This round is called the SS109, and there may be other nomenclatures of which I'm not aware.

    Most civilian rifles chambered for the .223/5.56 have a twist more suited to the lighter bullets. This includes the Mini-14, some AR-15s, and many others.

    Each weight will function with either twist rate... it's just a matter of which works best in your particular rifle.

    HEY GUYS!!... am I learning anything here, or what??

    Also, did I get it right?

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  • TED GAR
    My bushmaster Hbar 1/9 twist, does not like the 62 grain nato round. It prefers the 55 and 45 grain. As for your question..Yes the 223 is an American measurement. And the 5.56x45 is the metric measurement for the same caliber.
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  • fourdees
    The .223 vs 5.56 is indeed a confusing issue. My advise is to visit the AR15 web site and click on AR15 Community then click on Ammunition forum. Check out the AR15 AMMO FAQ. More info than you will ever need or want!

    Fourdees
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  • Chris78
    I'm no expert by far but I did read in a Bushmaster book that their rifles were suited for the 5.56, or the .223. To my understanding they are the same diameter, but the 5.56 is loader to higher pressures as stated in the above reply. This being said, I assume that shooting a .223 in a chamber suited for 5.56 should be fine, but not vice versa. Just my thoughts?
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  • Boomerang
    OK - straight from the experts mouth: Remington and SAAMI

    .223 Rem VS 5.56mm
    There are a lot of questions about these two cartridges. Many people think they are identical - merely different designations for commercial and military. The truth is that, although somewhat similar, they are not the same and you should know the differences before buying either cartridge.


    The cartridge casings for both calibers have basically the same length and exterior dimensions.
    The 5.56 round, loaded to Military Specification, typically has higher velocity and chamber pressure than the .223 Rem.
    The 5.56 cartridge case may have thicker walls, and a thicker head, for extra strength. This better contains the higher chamber pressure. However, a thicker case reduces powder capacity, which is of concern to the reloader.
    The 5.56mm and .223 Rem chambers are nearly identical. The difference is in the "Leade". Leade is defined as the portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. It is also more commonly known as the throat. Leade in a .223 Rem chamber is usually .085". In a 5.56mm chamber the leade is typically .162", or almost twice as much as in the 223 Rem chamber.
    You can fire .223 Rem cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity over firing the .223 round in the chamber with the shorter leade it was designed for.
    Problems may occur when firing the higher-pressure 5.56mm cartridge in a .223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads and gun functioning issues.
    The 5.56mm military cartridge fired in a .223 Rem chamber is considered by SAAMI (Small Arm and Ammunition Manufacturers Institute) to be an unsafe ammunition combination.
    Before buying either of these two types of ammunition, always check your gun to find what caliber it is chambered for, then buy the appropriate ammunition. Most 5.56mm rounds made have full metal jacket bullets. Performance bullets - soft points, hollow points, Ballistic Silvertips, etc. - are loaded in .223 Rem cartridges. Firing a .223 Rem cartridge in a 5.56mm-chambered gun is safe and merely gives you slightly reduced velocity and accuracy. However we do not recommend, nor does SAAMI recommend, firing a 5.56mm cartridge in a gun chambered for the .223 Rem as the shorter leade can cause pressure-related problems.



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  • hdrulz99
    Thanks for the clarification. I checked my Colt - it says 5.56 NATO, so I should be safe shooting these rounds, and maybe I'll pick up a little accuracy as well.
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