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.223 vs 5.56
It takes a number of steps to craft rifle brass. When it comes to .223 vs. 5.56, the 5.56 gets two stamps onto the head, to harden it more.


Editor’s Note: This article on .223 vs 5.56 comparisons is an excerpt from Gun Digest 2013, the world’s greatest gun book.

.223 vs 5.56: A History

To a whole lot of shooters, ammo is ammo—if it fits, it shoots. These shooters tend to be the guys with seriously tired, worn, or even busted firearms. They also tend to focus on the wrong thing; you know, the guy who scrubs the brass marks off his ejector lump, at least until one day his rifle stops working or breaks into many pieces.

Ammo is not ammo. And when doing a .223 vs 5.56 comparison, while the loads are almost identical, they are not the same. To know why, we have to go back to the beginning.

.223 vs 5.56 barrel
While it is comforting to read what is marked on the barrel, you can’t always believe the chamber designation. You have to do as Reagan advised—trust, but verify. An important thing to remember when testing .223 vs 5.56.

The early 1960s were an interesting time. The returning GIs from WWII and Korea had a decade to get things the way they liked. Two tastes they acquired during that time were varmint shooting and benchrest. Varmint shooting was simple. Various members of the rodentia clan, going about their usual business in a field or pasture, served as animate targets. They were prolific breeders, there was no limit, no season, no quitting. You could shoot all day if you wished. Well, as much as shooters then and now like to shoot, shooting varmints with a .30-06 was just silly. The recoil would beat you up, the noise was alarming, barrels got really hot really fast, and the cost of ammo, even back then, was just off the charts.

So they went down in caliber until they found that various rifle cartridges using .224-inch bullets did the job nicely.

Benchrest shooting was a refinement and variant of target shooting. Instead of trying to coax all the shots into a 10-ring, the group was the score. The smaller the group, the better the score. Again, smaller was better, and the common .224-inch diameter bullet served well.

The premier cartridge in the early 1950s, when varminting and benchrest got started and began revving up, was the .222 Remington. Introduced, in 1950, in the Remington 722, it was superbly accurate, and the rifle was also a brilliant out-of-the-box shooter. The mild recoil would not cause a benchrest shooter to have aiming problems, and the mild report, efficient powder charges and low bore erosion made it a useful varmint cartridge.

For those who needed more reach in the varmint fields, Remington came out with the .222 Magnum in 1958, offering 2-300 fps more velocity than the little .222.

Now we shift gears from varminting to the on-going soap opera of the U.S. Army rifle situation. Having spent a decade and millions of taxpayers dollars, the U.S. Army Ordnance bureau has brought forth … an improved M1 Garand. And so screwed up is the process that they can’t even produce rifles quickly enough to arm the U.S. Army in any reasonable time frame. I once looked into the numbers and came to the conclusion that, at the rate the Army was buying and building (the U.S. arsenal at Springfield was still open then), the entire U.S. Army would not have been switched over to the M14 before the bicentennial. For those who don’t remember that occasion, the year was 1976.

So, the Army finds, in the mid-1960s, that the Armalite rifle is one that could actually be forced upon them. They pull out all the stops and do everything they can to prevent this. “Real men shoot .30 rifles” was the prevailing ethos of the day (and in some circles, still is).

The cartridge the Armalite rifle was chambered for was the “.222 Special,” a case halfway between the .22 Rem. and the .222 Rem. Mag. It also split the difference between them in velocity. The Army, recognizing an opportunity, first accepted the velocity as sufficient. Then they upped the stakes and insisted on better and better down-range performance. Basically, they kept asking until they had exceeded the pressure limits of the .222 Special. But the problem is that pressure is not simply velocity-dependant. Still, the designers had managed to meet the velocity specs, and the rifle was adopted.

I have now, in less than 700 words, summarized years of work, 100,000 man-hours of engineering, manufacturing and range testing, and we’ve only begun.


  1. In response to Chick, yes- the longer throat does make a difference in accuracy potential If you are not a reloader, and use only commercial/military loaded ammo. The exterior cartridge case dimensions are exactly the same. Over -all length (OAL) may not be.That is determined by bullet weight! The original cartridge started out with a 52 grn bullet.This is when Remmington who had invested much in the way of the development of the finalized cartridge jumped on the commercial value as a civilian product ,had it SAAMI certified (5.56 x45Nato is not!). Hence …Ta.. Da! =.223 Remington.The only difference as you see, is in the area of the chamber in front of the case mouth.Military bullets weigh upwards of 80 grs. . Now as too leade,/Throat.Heavier bullets require longer throats,lest the bullet jambs into the rifleing .Now you talk about pressure spikes! Yikes!!

  2. If I found that the manufacturer of my AR type rifle wasn’t building a rifle that was capable of firing mil-spec ammo, not only would I get rid of the gun, but I’d make sure everybody at the local gun shops and on social media knew about it. It’s a long article for saying “don’t put hot loads in a weapon that’s not designed for it”.

  3. I am no expert but have had past opportunity to touch up-close those early M16 rifles. Between the M14 and the M16 the first noticeable difference is the very much reduced recoil/total weight of the M16/ammo. The M14 after 200 rounds in less than 1 hour the temptation to hold the butt away from the shoulder was nearly impossible to avoid. Today’s CQB (close quarter battle) tight-urban open-terrain evolution has several needs that one rifle just does not fit unless there is armored units alongside. ROE’s can significantly reduce any weapon system combination. This is a sin of ignorance. The current M4 variant is in a good shooters hand effective at 400-600M soft target, but best at the 0-350m. CQB is in part a product of WW2 and Offense Assault needs. Armored and Mechanized rapid assault requires somewhere along that line of operation infantry support at very close distances relative to the effective range of the armored-biggest gun.

    WW2 U.S. right-Flank Army ‘breakout’ occuring any number of times, a very popular weapon was the M-2 auto select carbines that the crew of M119(?) carried.

    IWS a derogatory term with the I-idiot and the S-stars knew very well, 1966, that units, some, assigned were not completing the mandatory repetitive weapon qualifications. Oh, the paper work showed fine-and dandy good work. One such solution was on a given day 6 shooters fire adequate rounds for each assign person/weapon and bag the empties and turn in to the IWS operatives ‘see, we have done our duty’. After 1000 Rd’s 7.62×51/M14 in one shoot, no more shooting for a week, maybe a month, recoil injury. The M16, also shot at these events would only get hot, sometimes ruining a barrel. The guy with the bum shoulder ended up loading Mags M14/tripod/auto.

    The war fighting evolution continues today. The German ARMP43 or variants began the Assault Rife evolution. A copy cat in the AK47 after WW2. The original Garand M1 development model had a banana magazine(30rn?) but IWS (maybe a bureaucrat) altered that notion and via another competing New-rifle that used the metallic Clip now famous in-sound M1 when the last round ejected. The term – ‘How many Clips you have left’vs magazine of today. BAR’ gunners called the bullet holder?

    In my opinion, which may not be much, the M16 development came about because of NATO needs and what would be a defensive CQB-urban envirnment. Protecting available defensive armor units from an invading offensive Warsaw PAC army equipped with the now famous AK47. Several of the then NATO allies had or were developing their own assualt-rife to fire the 7.62. The AR10, rejected by AMC, variant saw action in a foreign army before the U.S. completed M14 production. The turning point has to do with 1960-63 Air-Mobil attack functions – logistical considerations. Any number of M1 trained soldiers hated the 5.56 for most all of the obvious reasons. The most distractible complaint was that the M16 was worthless at dismounted drill. Worthless, they said.

    WW2/Korean vets mostly occupied any place of importance of the Cold War in the US military 1956-66. The last measurable front line offense vs defensive war was coming to an end. Gulf War 1991 was the ultimate test to this Defensive NATO vs Warsaw PAC capability in the Big D transitioning into the Offensive war that wins any war. Logistics win wars. Tenacity wins battles. A vet of Panama 82nd/Regiment jumped with twice the normal ammo for their M16’s. This was not possible at weight restricting 7.62. Thinking Logistics. The USSR converted over to a lower recoiled/weight 22cal AK74. Today’s soldier carrying an M4 is much better trained and skilled at most every thing war than in 1956. NATO EU 1965 was a cannon fodder strategy first hours-days.

  4. It’s funny, but I feel kinda stupid because it seems to me that what the military was looking for, and ended up with, was something very much like the carbine m-1. Light, maneuverable, moderate power cartridge, full-auto and hi-capacity magazines. Plus we had a s___load of them on hand. A little re-fitting and you never know……

  5. There is another element to all this. Back in the late 1960s I was working with weapons designers at Picatinny Arsenal. I remember having a fairly long lunch hour discussion with a man from Frankfort Arsenal. He described an outline of small arms development as follows. There was a desire to produce a weapon for ‘foreign national’ that was smaller and lighter than those carried by the folks in Europe and North America. (Like those folks in south east asia perhaps. It needn’t be said that the additional sales would be good for the arms industry.) There were other assumptions such as wounding the enemy was better than killing. In addition it was well known that long thin rounds become unstable when they pass into a new medium such as air to flesh and they are apt to tumble producing a nastier, but not necessarily a killing, wound. A ball for example just blasts on as far as it can. A piece of coat hanger wire will fly like an arrow and then will bend and tumble when it hits. The extreme military ’round’ in this regard was the flechette. There were even some experiments with flechette rockets that could be launched from within a soda straw or a cigarette, the filter protecting the person firing it from the back blast, but I digress. In any case the point was the ‘new’ military round was designed to be a maiming and wounding round and as such I think it is a bad choice for the military in situations where there is no enemy that will tie up its forces caring for wounded.