.223 Versus 5.56

Gunsmith’s should have the SAAMI-published list of unsafe caliber combinations detailing cartridge and chamber combinations that can be force-fit into a rifle and the combos that ought not be there. One surprising (to some) inclusion is the .223 Remington and the 5.56×45. While they are not the same and should not be used interchangeably, .223 is generally safe in the 5.56 but the reverse is not. How do they differ?

Given dozens of chamber dimensional drawings used by reamer makers, custom gunsmiths, and arsenals across America, we can’t cover every named variant. First, the two are the same in headspace dimensions. Consulting chamber dimensions reveals some combinations might suggest that one or the other won’t work, but the overlap of bolt face to shoulder dimensions is so great that it doesn’t matter. At least, not for this discussion.

The datum line and plus-or-minus of what is permitted for the shoulder location is not the problem here. They are also the same in listed chamber pressure but that takes a bit of explaining. Where they differ is in the leade, known as the throat, and how they are loaded. The .223 Remington was unveiled in 1962 but went into production a year or two later. Originally the .222 Special as an R&D cartridge for potential military adoption, it became the .223 Remington and was used in the then-new Armalite AR-15 rifle.

When Defense Secretary Mc Namara forced the adoption of the Armalite, requiring the dropping of the M14, the Army resisted. Top, we have the SAAMI .223 Remington chamber and leade with its short jump. Center is the common 5.56 leade with proper jump for a hot load. Bottom is the 5.56 M-Guns NEMRT (North East Multi- Regional Training) clean up reamer designed by Ned Christiansen of M-Guns meant to clean up any problems or disparities in dimension from the earlier chambering. Oh, they seemed on-board at first.

But then they started moving the goalposts. Literally. The original "We’ll be fine with helmet perforation at 200 yards" became 300, then 400, then 500 yards. To get that performance, the cartridge performance had to be throttled up. Armalite and Colt could not re-design the rifle to accept a larger cartridge as that would have killed the project. (Probably what the Army wanted, really.) So, they did what magnum developer Roy Weatherby had done for his cartridges by extending the leade.

This allowed for a greater powder charge while controlling pressure to deliver the velocity they needed to meet the Army demands for downrange performance. OK, a step back to internal ballistics. When the powder charge on a rifle is ignited, the powder burns from the base forward.

Unlike a handgun cartridge, where the entire powder charge can be consumed before the bullet even begins moving, and in many instances before the bullet has left the case, in a rifle cartridge the initial burning of the powder will push the unburnt powder in the column forward, and the bullet will jump free of the case. (This all happens in fractions of milliseconds.) That is why some cartridges will require a stout neck tension, or heavy crimp, in order to ensure proper combustion of the ladles of slow-burning powders used in them.

The bullet, having moved forward, in effect creates a larger case for the powder to burn in. A larger-capacity case with any given powder charge in it means it generates less pressure. However, when the bullet strikes the leading edge of the lands, it slows down. It has to, because it takes time and energy to engrave the bullet. The slowing bullet, while the powder is still burning, creates another pressure peak.

This is simply part of the gas laws, an aspect of thermodynamics that hit the newspapers during the NFL’s Deflategate episode. The slowdown, the stalling of the bullet in the engraving, is to a large extent the cause of the peak of the pressure curve. Without that slowdown, the peak would not be as great. (The only way to prevent that

slowdown is to eliminate rifling. That is a benefit not worth the cost.) So, what Armalite and Colt did was to move the engagement surfaces of the lands forward. They also made the angle of onset, the "ramp" of the rifling the bullet has to hit, more shallow on the 5.56. All of this reduces bullet stall and reduces the pressure spike that the stall creates. In essence, they found a "free" way to get more velocity from the same case and rifle.

As a tactical/engineering decision, they also relaxed the allowed diameter of the throat, the unrifled portion of the chamber, that being the space between the end of the case and the beginning of the rifling. This allows for more gunk, smut, debris, fouling, etc. to accumulate before reliability issues arise in a combat environment. Not always, and probably not often.

Other things break bolts, but the pressure spike of 5.56 in .223 leades causes other problems. 56—and it was marked by the barrel maker—for the company that built the rifle. Too bad it actually was a .223 leade. Oh, and an important detail to keep in mind: there is no SAAMI spec for 5.56 ammunition. Only military. And there is no military spec for .223 ammunition, only 5.56. So while we are not exactly comparing apples and oranges, we are getting perilously close.

So, what happens when we mix up the cartridges in our pressure barrels or firearms? Let’s assume for the moment that we’re dealing with .223 Remington and 5.56×45, each loaded to 55,000 PSI. Fired in their own chambers, they will post a maximum average chamber pressure of 55,000 PSI. Ho-hum. If we swap them, it gets… interesting. The .223 in the 5.56 chamber, because of the longer leade, will have a measured chamber pressure lower. Sometimes a lot lower. It can be as low as 46-47,000 PSI. The reverse?

That’s the bad news. The 5.56 fired in a .223 chamber can have truly impressive pressure spikes. If we start at 55,000 PSI in a 5.56 chamber, that same ammo in a .223 chamber can be 20%, 25%, or even 30% greater. I have had such ammo and chamber combinations pressure-tested that went from the low 50s in pressure when tested in 5.56 barrels, to upper 60s when tested in .223 barrels.

I have talked to ballisticians who have recorded pressure barrel readings with some 5.56 loads in the mid 70s when fired in .223 chambers. That is over the proof load. How can it be that they have the same pressures when loaded in their respective chambers but marked differences when mixed? The leade and the powder type and charge used in a .223 is done with the assumption that the bullet will be experiencing a short throat with a sharp-angled rifling onset.

The 5.56 is the opposite: the powder charge and type is selected on the assumption there will bealong leade and shallow onset to mitigate some of the extra powder (or slower-burning powder) used to gain the 5.56 performance. That charge, or burn rate, is what gives the 5.56 its 2-300 fps velocity gain over the .223. But it comes with the requirement of a 5.56 leade. What is the intermediate result of shooting 5.56 ammo in .223 chambers?

The first thought people have is "Bolts must break." This seems to not be the case as broken bolts we have seen in law enforcement patrol rifle classes don’t follow the pattern of "5.56 in .223 chambers" use. Usually, bolts break (when there is a pattern) when end-users have short-barrel rifles and put suppressors on them. That rifles do not come apart with the wrong ammo combination in this instance tells me that the designers and engineers who make them have done their jobs properly.

But that still leaves us, and our customers, with a problem. What happens when you fire a steady diet of 5.56 ammo through a rifle chambered in .223? And how can you tell which it is? Because a lot of the time the markings on barrels are wrong. I have found this out from years of working as an armorer and instructor in LE patrol rifle classes. Back in "the day" we saw a lot of "frankenguns"—home-built rifles and carbines.

In the last decade the numbers of those has dropped off markedly and almost all we see today are factory-built rifles. But the problem of .223 chambers persists. First, how it manifests itself, second, why there is a problem and why we can’t necessarily believe what we read, and third, how to solve the problem.

This is an expensive way to deal with the problem as the couple of thousand rounds (minimum) of ammo costs more than the barrel, or the reamer and gauge. 56 chamber (the case mouth will rest right under the "A" of NATO) has plenty of room and a gentle angle for the bullet to engrave the rifling. The problem with the over-pressure situation of 5.56 in a .223 chamber is not just in extra stress on the rifle. There is also the case to consider. The pressure is great enough to loosen primer pockets in a single firing.

In our LE classes, when it comes time to police the brass, it isn’t unusual (if we take the time to inspect cases) to find empty cases from factory ammunition lacking primers. This is obviously bad for the reloaders among us and our customer base. But also, you have to ask; where do those primers go? Most of the time, overboard and onto the ground, along with the case. But not always.

Before we started checking all rifles for .223 leades, we would have a rifle—or two or three—typically stop working a day or two into a class. The three and five day classes have varied over the years, but a 3-day class can count on 500 rounds and a 5-day class can now easily reach 1,000 rounds. Before ammo got expensive, and budgets limited, we were easily doing twice that and then some. The other armorer and I would find spent, expelled primers in the most amazing locales in the malfunctioning ARs in use.

The loose primers would rattle around in the lower receiver until they tied up the trigger, and once there would have kept a rifle from firing. They would bounce around in the upper, where they would often have to be fished out of the locking lug recesses of the barrel extension. The bolt can’t rotate closed when there is a primer in there.

They’ve been found in the carrier (the cam pin slots is equally unwilling to work with a primer in it) and once we even had to use a dental pick to pry the primer anvil out of the carrier gas key where it had separated from the primer cup and become lodged. All of these were discovered because the rifle stopped working. This would be very bad if the first shot lost a primer and the second shot was unavailable due to the primer being someplace it ought not to be. The most alarming one was also the most puzzling.

In a particular patrol rifle class, the line of officers had just finished a drill, and in the pause, after the drill-end whistle, there came a sudden "b-r-r-r-p!" Followed immediately by a "Patrick! Ned!" We were being summoned for a problem. As we walked up, the lead instructor told us and everyone there, "I was looking directly at him, his finger was not on the trigger." (Always good to have solid, dependable info on a problem.) What had happened?

At the end of the drill, the officer involved had followed the steps properly: scanned the targets, lowered his muzzle, and was applying the selector to Safe. It resisted, so he forced it, and that was when his semi-autoonly, factory-built carbine kicked off a three-shot burst. We gingerly took the carbine out of his hands, cleared the chamber, and then proceeded to perform a post-mortem on the carbine. We checked all of the usual suspects and found nothing.

We then slowly and carefully disassembled it, inspecting every part as it came out. The last to come out, the trigger, revealed a primer anvil, flattened, on the bottom deck of the lower interior. A-ha. We gauged the chamber. Yes, it had the expected .223 leade. We took care of that problem, scrubbed it up, and he ran the rest of the class without a problem. He had been using 5.56 ammunition. One round had the primer fall out of the loosened primer pocket and it fell into the lower.

There it got bashed up until the anvil came out and that bit of brass alloy had finally found its way underneath the trigger, causing the excitement. As far as we could tell, the anvil had restricted trigger movement when the safety was pushing on it, and the dimensional "float" of trigger, hammer and disconnector had allowed it to run away for three shots until the anvil was flattened enough to create clearance. With clearance, the sear could contact the hammer hook, and it stopped firing.

So, most of the time, the "popped" primer isn’t much of a safety problem. When it is, the usual result is that the rifle stops working. But

56 NEMRT reamer sets the leade just enough past 5.56 to clean up any errant problems that the chamber might have had. 223 leade with the dial calipers set to the distance of a 5.56 NEMRT leade. You can see the difference and the source of the problem. once, this time, it caused a misfire. Luckily (actually, due to good training) the officer involved had the muzzle pointed in a safe direction and was paying attention to what was going on. It ended up as a useful bit of knowledge, a great story, and no harm done.

Why is this a problem? That pressure spike. The stalled bullet with the powder charge meant for a 5.56 chamber causes excess pressure, expanding the case, and primers fall out. They even fall out of cases with crimped primer pockets. The excess pressure may not cause parts malfunctions but it can cause operational malfunctions. We cannot depend on the barrel markings to guide us. When we realized the 223 leade and not wedge in place in a 5.56 leade.

You can use ink, a Sharpie, or Dykem to mark the gauge and see where it is binding, if it binds. If it isn’t, then there’s no problem here. extent of the problem, we began gauging the leade on every rifle in the classes. In the first class we did this, four rifles failed the gauge having .223-sized leades, even though three of the four were marked "5.56". The fourth was unmarked. All four ended up having classic "popped" primer malfunctions in the next day of the class.

Once corrected, they did not cause problems for the remainder of the class. Why would a rifle marked "5.56" not have a 5.56 leade? Because, with rare exceptions, rifle makers do not make the barrels they use. They buy barrels from barrel makers. If the rifle maker does not gauge every barrel on arrival and insist on only accepting 5.56-leade barrels, they will invariably end up with .223-leade barrels. Why? My assumption is that this is due to accuracy.

It has become an attitude among AR-15 owners and buyers that it is their birthright to buy an off-the-shelf AR that shoots 1 MOA at most, or better yet, sub-MOA. Anything less accurate is a cheat. (We will leave uncommented-on the probable inability of most of them to actually shoot sub-MOA.) Any rifle that fails to shoot accurately will be blamed on the maker and returned. To cut down on the rate of returns, rifle makers will accept .223-leade barrels and a marginal increase in accuracy.

The vast majority of shooters will not put enough ammo through their AR to experience a popped primer. And even those who do shoot a lot, they will not often be feeding it a steady diet of 5.56-loaded ammo, and thus not experience popped primers. There, any popped primers that are observed will be blamed on the ammo, the heat, the lack of cleaning, etc. The shooters can be counted on, however, to note every group that fails the 1-MOA test and complain loudly if there are too many of them.

There is also the matter of wear. Each round fired erodes the throat just a bit. Without extensive testing it can’t be pinned down, but after a few thousand rounds, the spike has to be less extreme than when the rifle was brand new. So, if a shooter gets through a few thousand rounds without experiencing a problem, they may not know they ever had one. Erosion gauges are coarse instruments

for this kind of measurement. Unlike the old Garand gauges, with a measurement from zero to ten, the M16 gauge simply has a Pass/Fail line. In that regard, the worst rifle I ever gauged was an A2 frankengun. The officer who owned it had been using it as his patrol rifle for a couple of decades and we were having trouble establishing a starting zero on the first range session of the class. Finally, having exhausted everything else, I poked an erosion gauge into the chamber.

I thought it was going to fall out the muzzle, going a good eight inches down the bore past the Fail line. Despite this, he had passed the qualification course just prior to arriving at the class. So, while wear decreases the problem, there’s no way of telling what is what with an erosion gauge. There are some companies you can depend on. The exemplar here is Colt.

Say what you will about their customer service, parts supply, sales effort, etc., we have never gauged a Colt AR-15 or M16/M4 that showed anything but a 5.56 leade. So, how can the problem be measured, and then corrected? Ned That lets me know when it might be time to get it sharpened.

Christiansen of Michiguns LTD. (M-Guns.com, 269/273-GUNS) makes a special gauge and a reamer called the NEMRT (North East Multi-Regional Training) clean up reamer to correct the problem, so named as it is used by that law enforcement training team. The gauge is made to the maximum dimensions of a proper 5.56 leade. If you insert this gauge into a clean chamber, and it does not bind, stick or otherwise wedge in place, you have a 5.56 leade. If it does stick, then you have something less.

I have taken to using a Sharpie or Dykem and coating the gauge in black, then stuff it into the chamber. If there is binding, I can see where the ink has been rubbed off. This keeps me from getting a false negative when gauging, for example, a barrel that happens to have a .223 Wylde chamber. A .223 Wylde chamber might have a tight-enough neck with a 5.56-length leade that the gauge will show some resistance when used. Marking avoids the false reading. The reamer is a special design.

It is made like a chambering reamer but the shoulder has been ground to be a non-cutting, bearing-only surface, and a safe edge. The throat and leade are dimensioned to clean up any .223 leade, and produce a 5.56 leade instead. It is actually a bit over the "book" specs of the 5.56 in throat length (but not diameter) just to clean up any vestiges of .223 leade that might be there.

The non-cutting shoulder means you can rotate the cutter all you want; once it has cut the leade, it won’t cut more and you do not risk increasing headspace. And that is the problem when taking the shortcut of using a 5.56 chambering reamer to correct a .223 leade. There’s also the matter of bore material.

Ned has the reamers fabricated out a special alloy, and they have been given additional heattreatment so they will cut carbon, stainless steel, and through chrome plating. "Wait, I want chrome plating, I don’t want to cut it off." You have a choice: a .223 leade with chrome or a 5.56 without.

And to make the choice for you or your customer easier, the first place the chrome of your .223 leade will be burnt off is exactly where you’ll be cutting it, so you soon won’t have chrome there anyway, at least after a few practice sessions. So, an easy choice, really. What the reamer won’t cut (and will be dulled by) are barrels treated via Melonite. These are easy to spot once you’ve looked over enough ARs and most of them are 5.56 leade anyway.

A barrel given the Melonite treatment that has a .223 leade is a hopeless case and can only be dealt with one of two ways: feed it only .223 ammo or send it back to the maker with a nastygram. When I ream a chamber, I used a spring-loaded marker to stamp a single indent into the handle body of my reamer. If I use it on a chromed barrel I do a pair of dots, side-by-side. That lets me track use of the reamer and decide if it is time for are-sharpening.

The reamer comes in a handle that is also a storage holder, along with a correct-sized Allen wrench to disassemble from storage, assemble, and then return the reamer.

The M-Guns reamer has a "safe" shoulder and cannot increase headspace no matter how much you turn it. You need both to diagnose and then fix a leade problem. How much of a difference does this make? Ned once received a late-night phone call from a regional LE ammunition rep. His company had just delivered several literal truckloads of bonded, LE-purposed ammunition to a law enforcement agency. The agency was having no end of problems with their fleet of new rifles and the LE-specified ammunition.

If the rep couldn’t solve the problem, the agency was going to ship back the ammo and expect a full refund. And yes, their first thought was the ammo, not the rifles. Ned explained all the 223 vs. 5.56 leade details to the ammo rep. Yes, ammo companies don’t always have all the details on rifles and LE agencies are almost clueless when it comes to technical details. (Are you surprised?) He overnighted a gauge and reamer to the rep.

The rep went to the agency, and asked for the test rifle that had experienced the most problems. He then gave them the short version of all this info, gauged it, and it failed the gauge.

He reamed the leade and then had the agency rangemaster do full-auto mag dumps until they were all satisfied that the problem was solved. (We can only imagine the phone call to the rifle maker that followed.) So, if you have a malfunctioning AR, one that coughs up primers and parts of primers when you clean it, this could be the problem. Gauge, ream, and life is good.

As I recall, the ammunition rep took the reamer with him, and gave them Ned’s name and contact info for future use. .223 Wylde So, then what is the Wylde chamber? In an effort to gain the pressure control of the 5.56 but not give up the accuracy edge of the .223, Bill Wylde essentially took the leade length angle and throat length of the 5.56 and combined it with the throat diameter of the .223.

That is a short, sketchy and incomplete description of the work it took and the final dimensions he settled on, but it will have to do for now. This offers the best of both worlds and a lot of rifle makers have adopted. It is also the reason I use the Sharpie to see what the gauge is telling me. If I find the gauge has the ink rubbed off of the throat area but is not touching the rifling, the chamber has a .223 Wylde throat and does not need to be reamed.

If it is still popping primers with a .223 Wylde chamber and leade, then there are other problems that requires a different solution than chamber reaming. That said, the accuracy difference between .223, 5.56, and Wylde is probably too small for most shooters to notice. Yes, an NRA High Power shooter might be able to tell you how many X-ring hits he gave up with a 5.56 vs. a .223 Wylde leade, but then again, maybe not.

I have used rifles, carbines, and SBRs with 5.56 leades and reamed leades to easily drop 300 meter "Ivans" on a National Guard range and its computer-controlled targets. I’ve tested before-and-after rifles using magnified optics and have not seen a significant change in accuracy. For me, the pressure control is worth any potential (and as yet unseen) loss of accuracy. That said, I am not an NRA High Power Master-class shooter and don’t know how many Xs I might have given up. SAAMI vs.

CIP "But CIP lists a higher pressure for 5.56 than SAAMI does." Yes, and CIP measures pressure in a different location on the case as well. You cannot just look at the numbers as it is like comparing apples and oranges. The only way to know what a certain CIP-approved load does for sure is to test it in both CIP and SAAMI test barrels. When I find someone who has both of them, and they are certified and current, I’ll do that and report on the results. The SAAMI vs. CIP comparison is not unlike the old CUP vs.

PSI conversions. What the ballisticians found was that there was no universal "CUP times Xfactor equals PSI" formula they could use. Each caliber was a law unto itself and all the data had to be re-generated. So, if someone tells you that the CIP pressure for a given caliber is higher, lower, or the same as a SAAMI pressure, the polite reply to that would be, "Thanks." AG