What's the difference . . .

[tpcollins]

. . . between .223 and 5.56 NATO ? Thanks.

[PA-Joe]

5.56 higher pressure thicker brass but you can use 223 dies to reload them. You should not shoot 5.56 ammo in a 223 barrel.

[89blazin]

What about shooting a resized/reloaded 5.56 in a .223 barrel? Wouldn't the brass be now sized for the 223 barrel after using a 223 resizing die? I know you should use approx. 10% less powder due to the 5.56 case wall thickness...

[Unclenick]

None of the above. In comparing the bigger 7.62×51 NATO to .308 Winchester, you often see quite a bit of difference in brass weight and thickness between military and the civilian brass. But in 5.56×45/.223 Remington there is little difference. Indeed, you often find the military brass, like Lake City, actually averaging very slightly lighter than a some of the civilian brass. But the difference is small. While it's always a good idea to knock your load down at least 5% and work it back up when you change brass, you won't usually find you land on a significantly different charge weight between 5.56 and .223 brass. The military brass tends to be a little tougher, which is good for reloading life in an AR or other self-loader. Commercial Federal (not their military FC brass), by contrast, tends to be soft.

As to what the difference is between the cartridges, it's all in the chamber. If you read the NATO and civilian .223 pressures given by the CIP, they are identical. In this country we get a difference because we have two standards organizations (SAAMI and the Military) that don't agree on methods and standards exactly. The NATO spec chamber is made a little longer and wider and has a slightly longer freebore. This is to insure smooth full-auto feeding and to accommodate some extra long specialty bullets. But the effect on pressure is typically less than a percent, and can be ignored.

Many self-loaders are now offered with what is called a Wilde chamber, which is a compromise on size to give you good feed without being quite as loose as a NATO chamber. I believe the idea is not to have cases stretch quite as much as they can in the longer chamber, and so to have longer reloading life. But my Compass Lake built AR has a standard match chamber and has never suffered even a hiccup, so I don't don't think that the chamber difference is all that important within the limits that you get to clean and maintain the gun before more than 80 rounds plus sighters have gone through it (the NRA match course length). For a gun shooting hundreds of rounds a day before you get an opportunity to clean, the Wilde chamber might improve reliability.

[89blazin]

OK, different thought process than reloading LC brass for my M1A, and no need to reduce powder charge.

So a prior comment regarding not shooting 5.56 in a .223 barrel...I no longer shoot commercial .308 in my M1A chamber/barrel. I understand it can let the brass stretch too much. I did have an R&P case rip in half and had to use a broken shell extractor to get it out.

[Unclenick]

The only instance I'm aware of where you want to avoid a 5.56 round in the .223 is if it has a long ogive specialty bullet that could jam the lands on a shorter throat. I've yet to run into any, so this is mainly a theoretical possibility. If you've been in Gander Mountain or looked at online ammo sellers, you'll see a lot of Federal and LC M193 on sale to any and all comers, and a lot of it goes through Mini-14's and various .223 bolt guns.

One of the funny things in the standards is that the military used to rate the 5.56 for 50,000-55,000 psi, depending on the load, but that's as measured in a copper crusher, what SAAMI would call CUP, even though the military called it psi. Then when they went over to Piezo transducers, the military and SAAMI gear didn't seem to measure the same. The NATO countries use 430 megapascals (MPa), which converts to 62,366 psi as measure by Piezo transducer. They use that same number for both .223 Rem and 5.56 NATO. If you convert by approximation, the old military 55,000 CUP limit to psi, you'd expect a number more like that. But SAAMI used to rate the .223 at 52,000 CUP, and when they went to psi, they only went up to 55,000 psi.

Every cartridge I can find that SAAMI used to rate at 52,000 CUP, is now rated at between 60,000 psi and 65,000 psi, except the .223. I don't know why, but can only suggest it's an artifact of the measuring gear. If you buy .223 in a European brand, like Sellier & Bellot, it will be loaded to the higher pressure CIP standard, same as the NATO ammo. The guns have no issue with it. Barrel throats last longer with a milder load, though, so there is a benefit to shooting the SAAMI limit stuff in that sense.

I've actually got a bunch of Remington cases that went through my M1A six times, and never had a hiccup. Pulling a head off could be due to your chamber being longer or rougher than mine. Those factors could stretch the cases more. Also, my Remington .308 brass was made 20 years ago. The military brass does seem to be tougher, though, and that seems to be the case in 5.56 as well. Just not the heavier/thicker aspect like with the 7.62.

[rclark]

I seem to recall the twist rates in the barrel rifling are different, and optimized for a given bullet weight. The case itself being the same dimensions .....

[Jim243]

What about shooting a resized/reloaded 5.56 in a .223 barrel? Wouldn't the brass be now sized for the 223 barrel after using a 223 resizing die?

Yep, for all pratical pruposes you have a 223 case after resizing, if you know of a place that carries 5.56 dies, please let me know.

I find that the 5.56 has about 0.10 grains less space than the commercial 223 case, but as all things there are exceptions to the rule.

OK, different thought process than reloading LC brass for my M1A, and no need to reduce powder charge.

Not really unless you are at or above max load data.

Jim

[tpcollins]

The reason I asked was I got a flier from Cabelas that had an AR in 5.56 x 45mm for around $600. In the same flier they had 5.56 x 45 ammo on sale for $8 a box.

I don't see it listed in either of my reloading manuals or the Hodgdon reloading site. My concern was whether this was a rare crappy cartridge or what? Thanks.

[Bart B.]

Unclenick mentions:

As to what the difference is between the cartridges, it's all in the chamber. If you read the NATO and civilian .223 pressures given by the CIP, they are identical. In this country we get a difference because we have two standards organizations (SAAMI and the Military) that don't agree on methods and standards exactly.

Almost correct; here's some details.

Both commercial and military specs and pressure measuring gear was the same for decades. They both used Universal receivers and tight spec'd test barrels using the copper crusher discs in the Copper Units of Pressure (CUP) system. While an emperical way of measuring, it was fairly repeatable and therefore "good enough for government work." Biggest problem with both entities was they used the phrase "pounds per square inch" or abbreviated "psi" and it really wasn't that.

In the early 1970's the electronic strain gage system came about and was more accurate and easier to use. It really did measure psi directly but the numbers it came up with were higher than the old CUP system. Commercial enterprised switched over to it and used PSI numbers. The military stayed with PSI and still used the CUP system for years. I've not seen anything suggesting the US aresenals switched over to strain gage systems in several searches on line. I may just call Lake City Army Ammo Plant and ask them.

Here's a list of many cartridges and their pressure numbers in piezo strain gage and copper crusher gage measurements for reference:

http://kwk.us/pressures.html

Ane here's SAAMI's specs for all the cartridges they establish data for. It lists both CUP and PSI numbers which is interesting to compare for a given cartridge:

http://www.saami.org/specifications_...wnload/206.pdf

[Gunplummer]

Have to agree with that. The crusher method was not all that accurate. The difference lies in the chamber specs. Anybody that worked on guns in the military knew that for years. It is a recent "Discovery" that the military chambers and brass have different specs than SAAMI. Note the load book separations in recent years. It is possible to to have a military rifle with a chamber in spec but on the high limits and load a cartridge on the SAAMI low specs and have a dangerous situation. The body diameter on SAAMI spec ammunition has an average tolerance of .008 and that is a lot. The only time pressure becomes a factor is when the brass is thick and chokes the bullet at the neck. The fact that some military brass is tight in SAAMI chambers should have been an indication that the specs are different. How do you make the brass thicker with out making the neck diameter larger?

[Bart B.]

Gunplummer mentions:

The crusher method was not all that accurate. The difference lies in the chamber specs. Anybody that worked on guns in the military knew that for years. It is a recent "Discovery" that the military chambers and brass have different specs than SAAMI.

I don't know what you mean by "recent" for that discovery, but decent riflesmiths back in the early '60's knew about it when the .308 Win. was first used in competition. I learned that from them at the US Navy Small Arms Match Conditioning Unit back then when they began rebuilding Garands with 7.62 NATO chambered barrels.

'Twas also mentioned by the USN Rifle Team's Officer in Charge in 1971 at the Nationals when the M16 was first allowed in DCM/CMP competition. The barrels used in the USN rifles were made by Bo Clerke and had standard SAAMI spec .223 Rem. chambers. We got Remington primed .223 Rem. cases to handload Sierra bullets in.

The above aside, not a large number of civilians knew the differences back then in both cartridges' chambers.

[Unclenick]

The copper crusher was invented in 1860; the first Piezo transducer in 1922; the modern strain gauge in 1938. So there's been plenty of time for awareness of the measuring system issue. I suspect the continued use of copper crushers had to do with cost of buying and maintaining vacuum tube instrumentation for them and not wanting the cost of having to obsolete the old gear out.

If you read the #46 Lyman handbook (pp 116-131) they've got some 1970's era HP White lab tests using a single barrel with both a copper crusher and a diaphragm Piezo transducer on it. The simultaneous readings have the Piezo instrument reading mostly higher but also lower than the crusher under different conditions. It's clear from the scatter that the crusher is the one being squirrelly in this situation.

You can go back further to Dr. Lloyd Brownell's 1965 study at the U of M. He used strain gauges (which agree well with Piezo transducers) but includes some Piezo results provided to him by DuPont. So if DuPont had the Piezo data ready to hand in 1965, then they must have known of the problem before then.

Indeed, I suspect they suspected there was a problem long before there were either Piezo or strain guages. Take a look at the 1992 SAAMI specs on page 119 (page 125 the way Adobe Reader counts) is a chart of copper crusher tests of the same lot of .30 Carbine reference loads by 9 different labs. Velocities only vary about 3%, but pressures vary a whopping 23%, finding MAPs from 32,800 to 41,200 psi. That kind of inconsistency is all you need to know to realize a measuring system is not reliable.



As to military vs. SAAMI measurements, board member FALphil wrote a fairly detailed article on the subject of why people think military and civilian pressures are different when they aren't. It is here and is worth a read for more information on the pressure measuring mess.

Re current measuring systems, Mark Humphries, a frequent match winner or placer at Camp Perry and a retired Aberdeen Proving Grounds Test Director, posted in recent months that he'd spoken with people he still knew from Aberdeen and verified that Lake City has changed over to Piezo transducer equipment and retired the copper crushers. Jim Ristowe at RSI told me he sold a Pressure Trace strain gauge instrument to Lake City at one point, but heard no more about it and doesn't know where they went with strain gauge testing. So at this point, anyway, the military has new Piezo transducer psi numbers to work with, and the copper crusher psi numbers are obsolete everywhere except on the web, where they will probably persist into future decades.

Regarding the cartridge case dimensions, keep in mind that both .308 Winchester and .223 Remington are civilian versions of the military rounds, taken straight from military drawings. As an example, when someone posting at the Sniper’s Hide believed the 7.62 NATO cartridge case had different dimensions from .308 NATO, a fellow there was able to post a letter he had from Sellier & Bellot, which makes both CIP and NATO spec ammo. He said they have drawings from both organizations and they are identical. The same applies to the .223/5.56 NATO.

So how could a tight fit occur? Well, this will come as a shock to some, but the SAAMI chamber specs allow 0.003” of interference fit between a minimum chamber and a maximum size case at the shoulder datum, where the 0.004” longer NATO chamber does not. So a case doesn’t have to be out of SAAMI spec to cause some resistance. If you look through the SAAMI specs, many bottleneck rimless cartridges have some allowed interference fit, though some do not and the rimmed and belted cases do not. Hatcher showed a .30-06 shoulder can be set back -0.006” just by chambering rapidly in an Enfield, because the width of the chamber has room for the resulting swell of the sides, so this degree of interference doesn’t actually prevent function.

I‘ve heard speculation before that this interference allowance was a carryover from when headspace was measured to the wall and shoulder intersect of both chamber and case, making the chamber headspace number shorter because the chamber is wider than the case. But the idea was they carried that length difference over from the old system without the engineers noticing isn’t very credible. And if they simply wanted to reduce maximum case and chamber difference, why not just set the tolerances that way? I’ll have to ask SAAMI about it.

Most commercial ammunition manufacturers don’t like complaints, so you’ll find commercial case shoulders usually at least 0.002” shorter than a minimum SAAMI chamber is at the shoulder. NATO ammunition makers, though, can aim right at the middle length case specification value, which is only 0.0005” short of a minimum SAAMI chamber. When they err a thousandth or two on the high side of that number it makes no difference to a NATO chamber, but in a SAAMI minimum chamber it causes interference, and you feel it a little closing the bolt on that.

The loaded cartridge specification calls for the neck to be no more than 0.253” diameter over top of a loaded bullet. If you think you have neck interference, which would be unsafe from a pressure standpoint, just make that measurement. It’s much more likely to turn out to be the shoulder.

For grins I weighed ten randomly selected new bulk unprimed Winchester .223 cases, and got an average weight of 93.30 grains. 10 randomly selected Lake City new, unprimed bulk brass averaged 92.19 grains. The SG of cartridge brass is 8.53, so that amounts to 0.13 grains of water capacity if the outside dimensions are the same. It would take about 0.08 grains of adjustment to a charge of a typical powder to keep the pressure the same with that volume difference. Most loads I settle on will shoot well with ±1% of powder charge variance, but if you think you can dispense to better than 0.1 grains precision and see the difference on paper, then God bless you.

Actual case volume has to be measured because outside dimensions are often not exactly the same. You could have a wider head and more weight but no less capacity, for example. So your best bet, real world, is to fireform the cases and check capacity before resizing them. The number that actually affects pressure in your gun is the volume your case expands to in the chamber. Figure about 0.07 grains of powder charge change for each full grain of brass weight difference when dimensions are identical, or about 0.6 grains of charge difference for each grain difference in water capacity. You want to work up to a change, but it will come out in that ballpark when you are done.

Nick

[Bart B.]

Unclenick, that's good info for readers.

I agree about crusher gages being "squirrelly" as their medium (copper discs) require a lot of calibration for each lot before they're used. CUP is a rubber yardstick, but for decades it was the only thing around.

Best thing in your post was the link to info on civilian and military pressures with the statement in it: "....I came to my own conclusion that 308 Winchester and 7.62 NATO were completely interchangeable." These two cartridges get tossed into the internet boxing ring far too often to see which one comes out the "strongest" in the pressure game.

Thanks for the date of origin of the different methods. My guesses on them were within 10 years on the crusher system and strain gage but 15 years off on the piezo transducer.

[Unclenick]

Bart,

I like the rubber yardstick. I'll probably steal that.

It seems to me someone at Precision Shooting sent test loads around to different facilities sometime in the 90's and got so much variance in the copper crusher results that he concluded it just wasn't a very useful measure. Not only was the method funky but it also depended what technician you got on a particular day as to the result. Some guys just have a better touch with a micrometer than others, it seems.

Wm. C. Davis, Jr. mentioned that the same instrument and operator could one day get a very different reading from a lot of reference loads than he normally did, and put the problem off to there being some variable we still hadn't identified, but I think that was overly optimistic. Some other folks have pointed out that SAAMI fails to control for ambient temperature in its test protocol, and that could affect matters too. Overall though, the copper crusher method was just never as good as was originally thought. I don't know if the lead crushers used for shotgun testing and some sub-10,000 psi pistol cartridges were any better.

I would guess that if the same technician fired some reference loads in a crusher on the same day as he fired loads he was checking, perhaps even alternating them with the reference loads, he could probably say he had or had not exceeded the reference load pressures, but that would be about it. The absolute numbers just aren't very meaningful. Any way you look at it, the crushers are obsolete, and the places that still publish crusher numbers are, again, being optimistic. And consider that calibrated crusher slugs do that badly and then that some folks try to glean estimated psi numbers from case head expansion numbers, another metal deformation measurement except without calibrated metal, and you can see why Bramwell found almost 2:1 pressures causing the same measured expansion.

Sometimes physics just doesn't play nice.

[Bart B.]

Unclenick's comment worth quoting:

And consider that calibrated crusher slugs do that badly and then that some folks try to glean estimated psi numbers from case head expansion numbers, another metal deformation measurement except without calibrated metal, and you can see why Bramwell found almost 2:1 pressures causing the same measured expansion.

Then there's some folks (example, a moderator on another shooting forum) who claim that barrel steel does not expand any measureable amount until about 40,000 psi's attained. So I asked him that if that's true, how come Oehler's System 43 using strain gages did wonderful on shotgun barrels with 12,000 psi, .22 rimfire barrels at 24,000 psi and modern handgun cylinder/barrels at 36,000 psi. He threatened to ban me from the web site for such outlandish comments challenging a forum moderator's technical knowledge.

[a7mmnut]

Absolutely nothing. If there were, companies would legally have to post seperate pages for the different pressure loadings in all of the books, as in evidence with the older .45-70 Gov't. Only one entry exists for the .223/5.56mm in every single one of load manual manufacturers' offerings.

-7-

[Bart B.]

Jim243 asks:

... if you know of a place that carries 5.56 dies, please let me know.

Is your intension to size a fired case so it's headspace is at military specs?

You can full length size cases from either .223 Rem. or 5.56 NATO chambers with a .223 Rem. full length sizing die. They are adjustable in the press to set fired case shoulders to any dimension from the case head that's within military specs. I don't think the body diameters having to be the same is important; if they are then use a small base full length sizing die.

[Bart B.]

Unclenick mentions:

Actual case volume has to be measured because outside dimensions are often not exactly the same.

I've never been a fan of determining case volume by measuring the weight of water that just fills the case. The only real case volume there is that counts is when the case is pressed hard against the chamber walls and bolt face. That's when all cases have the exact same outside dimensions and only their inside capacity is the space the powder gasses are at. Thicker walled ones will have less volume for a given chamber and usually more weight as all cartridge brass is pretty much the same metalurgy. So I think case weight is a better measure of case volume; thinner ones will weigh less and therefore have more room inside when they're fired.

One could calculate the chamber volume (bolt face to chamber mouth with high school math then with the weight of cartridge brass calculate how much brass in grains it would take to fill the chamber. Then subtract case weight. The difference is the case volume when the round's fired. Cartridge brass (70% brass, 30% zinc) weighs about .288 pounds per cubic inch.

[hooligan1]

Wow bravo fellas, bravo!!

[Gunplummer]

I never even thought about pressure difference between SAAMI and military ammo. I am stating that the chamber and cartridge dimensions are different. I don't care what Sellior & Bellot say, they are wrong. A couple years ago I called SAAMI for a .22 Savage Hi-Power chamber print. The man on the telephone told me he never heard of it. I don't go by idle talk. The Frankford Arsenal said different, and I believe them. Military chambers are head spaced off the area where the shoulder angle and the main body intersect to the face of the bolt. SAAMI specs are called from where a (Not sure of size any more) .375 ball? touches the shoulder. This information is in the old NRA HAND LOADERS GUIDE if you can find one. I am guessing the pressure issue came up because a lot of SAAMI spec chambers "Choked" military ammo because it was oversize in the chamber. You screw up a reamer and get the neck undersize and watch the pressure go up. You think CIP specs match ours? I have never checked a 98 Mauser that did not fail the NO-GO gage made to SAAMI specs. I test fired every one of them with out a problem.

[Bart B.]

Gunplummer says:

A couple years ago I called SAAMI for a .22 Savage Hi-Power chamber print. The man on the telephone told me he never heard of it.

I would not have expected SAAMI to have a .22 Savage Hi-Power chamber print two years ago. Nor would I expect everyone at SAAMI to know about every commercial and wildcat cartridge made. There's no requirement that every cartridge be listed in SAAMI documents. That Hi-Power cartridge is the .25-35 case necked down to shoot .227" diameter bullets. It came about long before WWI at least a dozen years before SAAMI was instituted in 1926. SAAMI's online documents have the .25-35 chamber and cartridge drawing you could work from. In Europe, that old Savage round's called the 5.6x52mmR and ammo's still available there.

Military chambers are head spaced off the area where the shoulder angle and the main body intersect to the face of the bolt. SAAMI specs are called from where a (Not sure of size any more) .375 ball? touches the shoulder.

Both SAAMI .223 Rem. and military 5.56 NATO headspace gages reference a datum line on the shoulder that's .330" diameter.

I have never heard of any rifle chamber headspace reference is off the area where the shoulder angle and the main body intersect to the face of the bolt. I'm trying to picture this in my mind but cannot. Both cartridges' shoulder angle is 23 degrees. No way does a line through the shoulder go through any point in the bolt face.

What's a web site url that shows this in a diagram?

[Gunplummer]

Buy an old NRA Handloaders Guide, they are around. Education is expensive and I am not loaning you mine. It is a wealth of information from the Frankford Arsenal and Norma testing. Yes, I expect everyone but the Janitor at SAAMI to know what a .22 high-power is. I have 2 boxes of Remington that look as if they were manufactured in at least the 60's.
There was no SAAMI site on the internet at the time and you had to deal directly with SAAMI. Yes, you had to pay for the books but they would send you the up dates. The book really did not have a lot of cartridges listed, but it did have a .303 Savage listed so I thought maybe the .22 HP was in their archives. I don't care what your position is on chamber drawings as it is only an opinion drawn from bad information. I suppose next you are going to tell me that the older load books did not have higher max loads listed because you can not find it on the internet?

[Bart B.]

Gunplummer exclaims:

I don't care what your position is on chamber drawings as it is only an opinion drawn from bad information.

Shame on your for making that erroneous assumption. I'm gonna tell your Mommie on you.

My position on chamber drawings is a long way from an opinion drawn from bad information. It comes from the SAAMI documents that are available to everyone. Note that it's voluntary that arms and ammunition companies submit their cartridge and chamber specs to SAAMI; no law makes it mandatory. Which is why a lot of cartridges are not listed in SAAMI documents.

Download the publications you want for free from the SAAMI links below then save them (they're a bit too big for printing):

For centerfire rifle cartridges:

http://www.saami.org/specifications_...wnload/206.pdf

For centerfire pistol and revolver cartridges:

http://www.saami.org/specifications_...wnload/205.pdf

For rimfire cartridges:

http://www.saami.org/specifications_...wnload/208.pdf

Here's links to SAAMI's list of individual cartridge chamber and case specs. Open the one you want then click on the cartridge desired. A single page shows up for one cartridge that's easy to print or save:

For rifle:

http://www.saami.org/PubResources/CC...0-%20Rifle.pdf

For pistol and revolver:

http://www.saami.org/PubResources/CC...-%20Pistol.pdf

For rimfire:

http://www.saami.org/PubResources/CC...%20Rimfire.pdf

Check out the following and all its links for all sorts of info on SAAMI:

http://www.saami.org/index.cfm

Then Gunplummer makes another erroneous assumption:

I suppose next you are going to tell me that the older load books did not have higher max loads listed because you can not find it on the internet

The only thing I'll tell you next is you should learn what the facts are on anything from reliable sources before forming an opinion about them to base a comment on.

[old roper]

here is the difference

http://en.wikipedia.org/wiki/.223_Remington

http://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO