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
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About the Author: Patrick Sweeney is the author of many of Gun Digest books' best-selling titles, including Gun Digest Book of the 1911, Vols. I & II; Gun Digest Big Fat Book of the .45 ACP, Gun Digest Book of the AR-15, Gun Digest Book of the AK and SKS, Gun Digest Book of the Glock and Gunsmithing: Pistols and Revolvers, among other titles. A master gunsmith, Patrick is also Handguns Editor for Guns & Ammo magazine.
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