Ask Ian: .223 vs 5.56 and “Military Grade Ammo”

From Michal on Patreon:
“Can you talk about difference between .223 Remington and 5.56 NATO? Or in more general terms about possibility of using military grade ammo in civilian rifles. I heard everything from ‘it will explode’ to ‘it will work normally’.”

The short answer is that the difference between .223 Remington and 5.56mm NATO is immaterial to most people. It’s better the use .223 in .223 chambers in the long run, but really not a big deal. There is an excellent article on this written by Andrew Tuohy on the LuckyGunner blog.

As for military grade ammunition, it is really no different than civilian packaged ammunition. Some folks with minimal firearms experience have the notion that commercial ammunition is somehow derated in quality or capability compared to military ammunition, and this is simply not true.


  1. older .223 rifles might have the wrong twist rate for GI ammo. Newer rifles have a faster rate and can stabilize the longer bullets in military ammo. Of course, that only is important if you want to hit something. A great many shooters of 5.56/.223 seem only to want to make a lot of noise and produce a big pile of empty brass. present company excepted of course.

  2. Military grade ammunition is designed to fit military specifications for accuracy levels that are far larger than what civilians find acceptable for their rifles. Also, the military issue heavier for caliber bullets may not stabilize in early manufacture rifling twist rates which have changed over time. Original twist rate was specified as 1 turn in 12 inches, standard for military is now one in nine, which you can buy AR 15 uppers with the faster twist, but many older bolt actions/single shots/pump rifles cannot easily or cheaply be converted. There are very large numbers of these older twist rifles in use around the world.

    • Current US military twist rate from the M16A2 to today is 1:7″ twist for 5.56x45mm rifles & carbines. 1:7″ twist stabilizes the M856 tracer, companion to M855, the 62 grn green tip NATO round, which will stabilize in a 1:9″ twist bbl, the M856 tracer being longer. M855 will not stabilize in a 1:12″ twist bbl, unlike the 55 grn M193 ball round. I believe the Swiss use a 1:10″ twist for their 63 grn ball that doesn’t have the SS109 steel penetrator, and thus the bullet is shorter & stabilizes fine in the longer twist rate.

  3. Hi Ian and everybody, this seems to be an ongoing myth. The same for .308 Winchester and 7.62×51 NATO.
    In South Africa(which is no different to anywhere in the World!!! imagine, except for the corruption levels)we shoot all 4 “calibers” in all the relevant rifles,military and civilian, FN/R1/FAL/SLR whatever floats your boat and R4/Galil and they all shoot
    just fine. Thanks for your articles and videos Ian, you rock. Have an awesome December.

  4. According to Cartridges of the World, U.S. milspec 5.56 x 45mm ammunition (specifically M193, M855, and variants thereof) are spec’d for the U.S. and NATO standard chamber for that caliber. The dimensions are not the same as the SAAMI standard for commercial .223 Remington. SAAMI standards are in fact tighter than NATO/U.S.

    As such, rifles with SAAMI spec chambers may have problems with extraction. This is a familiar phenomenon to owners of Ruger Mini-14s. I know because I used to be one. Combined with (1) its uncomfortable stock (why the square-corned comb FGS?) and (2) the inability to safely fire it from the left shoulder (getting hit in the face with spent hot brass is not my idea of a wonderful time), I disposed of it to someone I knew was right-handed and only used commercial .223 Remington ammunition to get the varmints out of his vegetables.

    Ruger for years claimed there was no problem except in peoples’ imaginations. Then they came out with their own version of the AR-15, carefully telling everyone that it had a milspec chamber and bore with 1:9″ rifling.

    Finally, three years ago, they announced that the Ruger Mini-14 “now” had a chamber and bore congruent with milspec 5.56 x 45mm. A tacit admission that older Mini-14’s do not.

    COTW also defines milspec 5.56 x 45mm as essentially a “.223 Remington +P”. I would consider that a reasonable assessment.

    The bottom line is, use a rifle with a 5.56 x 45mm NATO chamber and bore spec for 5.56 x 45mm NATO ammunition, regardless of the “age” of same. Restrict rifles with SAAMI standard .223 Remington bores and chambers to commercial .223 Remington sporting ammunition.

    Or just get a rifle with the NATO bore/chamber spec’d barrel. It won’t care what you run through it as long as it’s nominally a 5.56 NATO or .223 round.



  5. A note about bullet (not cartridge, bullet) lengths:

    Commonly available 55 grains bullets have a length of around 0.740″ (see PMC Bronze .223 Remington and PMC X-TAC 5.56 NATO:

    The 55 grain bullet is what most “.223 Remington” chambered firearms are designed for – and they will almost always have a rifling twist of 1:12″ (one turn n 12 inches.) This twist rate was also true of military 5.56 NATO rifles designed for 55 grain bullet in the M193 cartridge.

    The longer a bullet is the faster is must spin to be stabilized.

    When you see that a .223 or 5.56 cartridge has a heavier bullet, for example a 62 grain bullet (such as the M855 military cartridge) that bullet is longer than a 55 grain bullet (around 0.923″, see and requires a higher twist rate to stabilize it.

    Firearms designed for 62 grain 5.56 ammunition typically have a twist rate of 1:9″

    You will also see heavier – and more importantly LONGER – bullets such as 77 grain, for example this PMC X-TAC Match cartridge in .223 Remington ( has a 77 grain bullet that is 0.983″ long: even longer than a 62 grain bullet and for these buckets people look for a barrel with a 1:7″ twist rate.

    For more on twist rate and bullet stability see:

  6. I think part of the confusion regarding 223/5,56 come from their pressure specifications. SAAMI and NATO use different pressure measurement methods that can not be directly compared.
    Regarding milspec, do not forget some 5,56 loadings are not strictly NATO compliant. Some ammo types are quite hotter, for instance US M855A1.

    • Also, there are very small dimensional differences in leade/freebore in military rifles to allow the longer, heavier bullets to not jam into the rifling before firing. This can boost pressures in sporting make rifles beyond safe limits. Then the history of development of the 5.56mm is worthy of a short book of its own. Multiple types of powder created to meet specific user requirements, different service branches conflicting standards etc. a fascinating development story.

    • Looking at the Wikipedia pages for both, it seems (but might not be) that .222 Rem Mag was developed after .223 Rem had already been developed up from .222 Rem to meet CONARC military specs and the ArmaLite AR-15 was in testing, it would seem to just be an accident of history. Their development seemed to have only been roughly a year apart, or maybe slightly less.

      • .223 was originally called the .222 Remington Special. Another name for it was .224 Winchester. It did indeed predate the .222 Remington Magnum, and rather quickly rendered the latter an also-ran. As Warren Page said in The Accurate Rifle, when you see a bolt-action varmint or benchrest rifle in .223, you’re seeing what otherwise would have been a .222 Remington Magnum.



  7. Thanks Ian,

    Bullshit STILL baffles brains, it seems.

    A long time ago I owned a wonderful fully-stocked short military Mauser carbine, made in Spain. It was a cavalry carbine and still had the 3″ (?) ring for a leather strap. And, the rider could drop the weapon without losing it.

    It was in many ways the best feral-pig (wild-boar) rifle I ever had. Australia has a lot of these pests.

    They can get big enough to be glad you have back-up shots, when they don’t go down as quickly as one expects.

    It was a very handy gun in our thick mountain forests, and being light was easy to manipulate in such scrubby, thorny country. (Blackberry bush is endemic down here – introduced species).

    It did kick a bit if you didn’t hold it fairly tightly.

    But that became natural quite quickly.

  8. One thing that needs to be pointed out, sadly, is that not all “MILSPEC” ammo in a given caliber is necessarily equivalent to similar ammo loaded by a different country.

    I can attest from harsh personal experience that the 5.56mm NATO load that Radway Green used to produce for British Army use in the SA80 series of weapons is emphatically not an ammunition that you’d want to try doing a one-for-one exchange with for your AR-15. The Brits were issuing stuff for the SA80 that was positively filthy, and which rapidly clogged the ever-loving snot out of the M16A2s I fired it out of. Likewise, the US Army-issue M855 that we tried out of the SA-80 produced notably higher velocities and much more bolt thrust out of the SA-80. You could stand there and tell, from ten yards away, that the ammo was notably producing much different results in the different weapons. What is optimized for one weapon ain’t necessarily so for another…

    Then, too, note the issues we had with M855 out of the M4 carbine. That load was never really validated thoroughly, because when the M4 was adopted, it was an afterthought that was supposed to go to support troops that weren’t going to be likely to go into direct combat. Unfortunately, the Infantry followed their desire path forward, and glommed onto every M4 they could get, and it wasn’t until 2007 and a shed-load of apocryphal reports that we got the ammo optimized for the M4, the M855A1.

    All things being equal, even MILSPEC ain’t necessarily what you’d think it would be. That little cross-in-circle on the headstamp doesn’t always mean as much as you would think…

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