.223 vs 5.56: Solving the Problem
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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: Solving the Problem

One solution would be to only use .223-spec ammo. That can be okay, but, if you find a deal on 5.56 ammo, it kind of makes no sense to buy a “deal” you can’t use. Also, some of the best ammo for some applications is 5.56-only. Plus, you can’t control the outside temperature and probably not how much ammo you may need to fire. It would be nice to have a rifle that handled 5.56 with aplomb. But how? To begin with, you have to be able to measure what is there.

The first thing you have to know is this isn’t about headspace. A headspace gauge only tells you the dimensions of the shoulder and case body, not the neck and leade. You need a leade/throat gauge, and for that you need to get a .223/5.56? Gage (yes, the “?” and misspelled “Gage” are the part of the correctly named product), from Michiguns (www.m-guns.com). I have to be up front and tell you that I have known Ned, the inventor, for nearly 30 years. I don’t get anything but thanks from him for recommending his great gizmo, and I think it is useful enough that I’d recommend it if I didn’t know or even like him.

The Gage is simple and ground to just under the maximum specs of a 5.56 leade/throat. Drop it in and, if it drops free, you have a 5.56 leade. If it sticks (it is hardened steel, don’t pound it in), you have a .223 leade. If you’re curious and want to know just where exactly it is catching, you can mark it up with a felt-tip pen and, with a little careful turning (clockwise), you can see where it rubs. If you are really curious, browse through your Brownells catalog—you do have a Brownells catalog, don’t you? You don’t? Get one, before you get severe deductions from your man-card—and order Cerrosafe. Cerrosafe is a special metal alloy with a low melting point. You push a cleaning patch until it is in front of your chamber, heat the Cerrosafe, pour it in the chamber and let it cool. Once cool, you push it out of the chamber, and now you have a cast of the chamber, throat, and leade. You can inspect and measure to your heart’s content.

So, with the Gage or Cerrosafe you find that you have a .223 chamber and you wanted a 5.56. If the rifle is still brand-new, you can send it back. However, the maker probably only has more barrels of the same kind from the same maker, and you may not get a 5.56 no matter how many times you ask. So, you need a specialized reamer. One that cuts the leade and the leade only. (You don’t want your headspace changed.) Ned makes that, also. Now, I can hear some of you saying, “But, I have a chromed barrel, I don’t want to cut the chrome!” Okay, stick with a chromed .223, that’s fine.

But, if you want a 5.56 leade, yes, the reamer will remove chrome. But guess what? The area being cut is the area where the chrome is blasted off first, so if you’ve put more than a few hundred rounds down your barrel, there’s probably not much chrome left there anyway, especially if you did rapid-fire shooting or heated the barrel up to the point where you had to wait for it to cool.

In all fairness, you don’t have to have Ned’s reamer. Other various reamer makers will be happy to supply you with a 5.56-spec finish reamer. You just have to be aware that a finish reamer will also ream the shoulder, if you aren’t careful. So, you may go in attempting solely to make a 5.56 throat and end up creating excessive headspace along the way. Ned’s reamer does not cut on the chamber shoulder at all, therefore, when you feel it stop cutting, you are safely done. It also makes a leade longer even than that of 5.56, though by a small margin.

What’s that, another protest? “But my barrel is marked 5.56, I can’t have a problem.” Alas, that is not the case.

At my latest LEO patrol rifle class, I chamber-gauged the two dozen rifles the officers had brought. All but two were marked “5.56.” One of those was an M16A1 and the other had a completely unmarked barrel. Of the 24 rifles, six failed the .223/5.56? Gage test. Two of those were not just .223-chambered, but clearly on the small side of the dimensions, as I had to use force to remove the Gage.

How can this be? Remember how barrels are made. The manufacturer uses a chambering reamer to turn the chamber out of the back and of the barrel blank. As reamers dull, they are re-sharpened. Each sharpening makes them fractionally smaller. Reamers start at the maximum size and, as they “shrink” from repeated sharpening, the chamber they cut also changes. Once they get to the minimum, they are discarded and a new reamer is employed. Well, some use reamers for a bit too long, and the chamber cut can be at minimum or smaller dimension.

Of those six that failed the Gage, three ended up showing pressure signs later in the class, so we reamed them with the Michiguns reamer and those problems went away. Two of them were the markedly undersized barrels. The other barrels/rifles continued to work, but for how long? They may have been getting fed .223-pressure ammunition, and thus would not show pressure signs.

Having a .223 chamber in your AR is a greater concern than just the social ostracism of having a rifle that is “not Mil-Spec.” However, it is something you can test and fix, if needed. Me, I’ve long-since checked all my rifles, and those that didn’t pass the test have been corrected.

Read More About the .223 vs 5.56

Gun Digest 2013 67th Edition BookThis article is taken from Gun Digest 2013, the world’s foremost firearms annual book. Keep reading in-depth ammunition articles when you order Gun Digest 2013.

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  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.