Chamber Differences For The .223

Howa Mini in .223 Remington

Q: I’ve been given some military ammunition for the 5.6x45mm NATO which I’ve been told is safe for use in my Ruger .223 Remington. But an article in an American magazine warns against doing this. Who is right? Can I safely shoot this ammo in my gun? Ken Galvin

M4 in 5.56 NATO

M4 in 5.56 NATO

A: I would be wary about using shooting military 5.56x45mm ammo in a standard sporter. There are significant differences in the chamber throat area; military arms usually have very long throats which allows a lot more room for expanding gases to occupy and reduce breech pressures. Sporting rifles have a shorter throat because they generally use lighter (shorter) bullets which have less distance to travel before they engage the rifling. The NATO chamber stemmed from a need to handle different ammo from different manufacturers of mil-spec cartridges which are normally loaded to pressures, up to 15,000 psi higher than sporting .223 ammo.

However, .223 rifles used for big-bore shooting usually have a faster rifling twist and long-throated (NATO- spec chambers) to handle longer, heavier .224 bullets like the Sierra 80gn HPBT MatchKing commonly used in “big-bore” competition. The long NATO throating allows this bullet to driven at up to 2900 fps! This is why NATO-spec ammo is not safe for use in a standard .223 rifle. Some commercial sporters are available which have a fast twist and long throat to handle longer bullets, but they usually have 5.56/.223 stamped on the barrel.

5.56x45 NATO vs .223 Rem.
5.56×45 NATO vs .223 Rem.




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Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.