Can somebody simply and concisely list the differences between the .223 Remington and the 5.56 X 45 NATO?

And then tell me how to know which rifles can shoot both and not?

There are two differences to be concerned with - max pressure and throat.

Pressure: The 5.56mm pressure specification is governed by to NATO EPVAT and not SAAMI or CIP. The NATO EPVAT measures pressure in a different area and using different types of transducers than SAAMI. NATO EPVAT maximum service pressure for the 5.56mm is 62,000psi and SAAMI maximum service pressure for the .223 is 55,000psi. Confused yet? To make matters more mixed up, CIP, the European standard, uses NATO EPVAT for .223 pressures. Bottom line is that it is not uncommon for 5.56mm ammunition to be "hotter" than US made .223 ammunition.

Throat: This is the most important difference. 5.56mm chambers are made with a longer throat than SAAMI standard .223 chambers. This has caused a lot of confusion and several manufacturers have adopted proprietary throats that are supposed to handle both cartridges.

If the barrel says .223 Remington - don't use 5.56mm in it. Doing so may result in higher pressures than the firearm was designed for. You may never see a problem but, then again, you might.

If the barrel says 5.56mm - you can use either 5.56mm or .223 Remington. Because of the differences, you may find a difference in how well the two types of ammo group.

If the manufacturer claims their proprietary chamber will handle both 5.56mm and .223 equally well then you are fine with either though, again, you may find the rifle favors one over the other.

The case dimensions of both are identical.
The chambers have different throats.
The 5.56 NATO is loaded at higher pressure than the .223 Remington, the length and shape of the throat in the 5.56 allows this. You can fire .223 in a NATO chamber with no problems.
Some .223 rifles seem to fire 5.56 with no issues,but I don't recomend it. Both of my .223 bolt guns don't like it. It takes a hammer or a heal to open my Remington M700 after firing a real 5.56 round. My M70 has
a definite "feel" when lifting the bolt after firing a 5.56mm round. I understand that some new bolt guns are chambered for 5.56mm/.223 solving the issue.

I sent you an email ledvm. Should clarify. Nate

quote:

Originally posted by BigNate:
I sent you an email ledvm. Should clarify. Nate

From BigNate:

Soooo, one has a long throat and the other doesn't?? that can apply to all calibers, WBY has long throated rifles and so do many custom guns, as do all Brno small ring comm. mod 21s and 22s. and they don't change the name of the caliber..Is this a black gun thing or what is the reasoning behind it..

Correct me if I'm wrong, but the 5.56 and the 223 are one and the same.

The only reason the pressures are higher for the 5.56 are due to where the pressure is measured (NATO measures at the neck), whereas SAAMI measures the 223 at the body. For some of us older guys, remember back in 1980 when the horsepower dropped on car engines? This was due to SAE rating the HP at the drivewheel, instead of at the flywheel (the tranny and driveline absorbs a lot of HP), same engines/performance, but 'less' HP.

The longer throat of the 5.56 guns is due to the increased usage of heavier (read: longer) bullets in military rounds. Jamming a bullet into the rifling will/should increase pressure.

I think if you look at when the 5.56mm was adopted by the military you'll see it was probably comercial first. Most Military rounds are long throated I believe.
The only time I'd be concerned about the difference in the throat differences is when going with the really long bullets. The 55's are fine, the 62gr are probably ok, but 69 and up may be something to consider.

I would suggest the last two posters go back and read Matt Organ's post. External dimensions on both cartridges may be the same, but there is a reason the head stamps are different.

So...a 5.56 X 45 with a 55 grain bullet should do fine in a .223 Rem bolt action rifle that shoots 55 gr bullets fine???

quote:

Originally posted by ledvm:
So...a 5.56 X 45 with a 55 grain bullet should do fine in a .223 Rem bolt action rifle that shoots 55 gr bullets fine???

Despite some truly excellent responses, you have somehow gotten it exactly wrong.

"5.56" (stamped on the box you found at Dicks) ammo may/may not generate excess pressure in your .223 chambered bolt gun. Generally unobtainable NATO-spec 5.56 ammo will generate excess pressure in your .223 bolt gun. And no, it is not just a matter of where pressures are measured.

It is true many people ignore the admonition concerning 5.56, ie., they are doing what SAAMI specifically says not to do. They usually get away with it. Why? Well,most people do not possess true NATO-spec M855 or even real M193. Most knockoff "5.56" (like Fed AE, XM193, XM855PD, etc.) loaded for consumers is really loaded to roughly .223 spec and gives lower pressure/velocity than M855 and M193.

I have cases of milsurp M855 and M193 that I run in M16s. As an example, some lots of M193 give an honest 3400+ fps from 20" barrels. You will not get that from the stuff you buy at Dicks and Walmart. I would never fire this ammo, or any NATO stamped loading, in a .223 chamber. YMMV.

Finally - to add even more confusion - a friend in the industry tells me AR rifle/bbl manufacturers got so sick of dealing with the confusion that their ".223" stamped chambers are often/usually 5.56 dimensionally. Can't blame them - we are living in an age of litigation. Remember, I said ".223" stamped ARs - I did not say bolt guns.

Sam

Sam,

I did not get anything wrong. I learned what I wanted to know. Notice the 3 ?'s after my question. I get what you are stating and had already gathered that. Basically even though the brass is the same externally as the .223 Rem, and the bullet is of the size commonly used in .223 Rem...the loads are or can be 'too hot' to have safe pressures in the chamber dimensions used in some if not most standard bolt action .223 Remingtons.

Sorry if I didn't recognize the significance of the three question marks.

The answer to this question: "so...a 5.56 X 45 with a 55 grain bullet should do fine in a .223 Rem bolt action rifle that shoots 55 gr bullets fine???" is maybe.

While most recent commercial 55 gr fmj loadings are likely OK, you do not want to run M193 through your .223 chambered bolt gun. Same goes for some earlier M193-spec clones; an example is the Norinco that was imported back in the '80s.

NATO-spec M855 and M856, etc., were not the first 5.56 service ammo to run above .223 SAAMI specs. The .223 Remington was a commercialization of the then still evolving military round. In order to develop specified ballistics for the 55 gr M193 used in southeast asia, it was necessary to load the ammo pretty hot. The later long throating and NATO standards are not the whole story. Even after M855 was developed, M193 continued to be produced. I've got M193 from RSA and from Guatemala. Have also a supply of "M855" from UAE (Abu Dhabi). Your guess about pressure levels and standards used is as good as mine.

The M193 story is well-covered in 'Black Rifle', by Ezell and Stevens.

Sam

You guys need to listen to Sam. He's got it right. He's also right about reading the book "Black Rifle" It describes how they came about to develop the 5.56. There were many other .224 caliber cartridges. I believe the initial idea of the 222 Remington Magnum was as a military cartridge. The 5.56 wasn't initially developed to use ball powder. It was using Dupont stick powder in it's infancy. The switch to ball powder while Nam was going on was ONE of the problems that gave the M16 a bad name back then.

I've also become aware that some manufacturers are using a 5.56 NATO chamber on their rifle so this problem doesn't crop up.

Weatherby used a very long freebore in order to achieve their high velocity without initial high pressure when the bullet enters the throat/forcing cone/bore. They wanted the bullet to get a start without friction/high pressure. You can build a rifle for Weatherby cartridges with "normal" freebore but you had better work your loads up and not shoot Weatherby ammo in them.

Sam,

Good info.

Have you ever sent a few of the NATO-spec M855 or M193 cartridges to a pressure proof house?

quote:

Originally posted by k-22hornet:
Have you ever sent a few of the NATO-spec M855 or M193 cartridges to a pressure proof house?

No, but if I could get my hands on some properly stored VN era M193 and some current issue M855 I'd be tempted to compare them to domestic boxed "5.56" 55s and 62s.

Few realize just how difficult it is for civilians to get their hands on US M193 or M855, ie., first tier. Most of what we get by way of bulk purchases is from other countries. If from the US it is 2nd or 3rd tier (ie., rejects). Pressure data might not correspond.

Sam

This whole question is a great exercise in futility. I have two ar-15 type rifles. I actually kinda assembled both. By that I mean I purchased bottoms then tops and actually pushed the 2 pins in to assemble them. There is one funny thing about both rifles. There is absolutely NO caliber marking on either. One is a 16" chrome moly barrel purchased from Midway (lowest priced upper they had at time,actually only one). It is not even marked with the manufacturer any where. The other is a Rock River with a SS 24" heavy varmint barrel. Rock River states in their data that it has a 'Wylde Chamber' whatever that is. Actually don't remember if the Midway upper said 223 or 5.6 in the ad. If it is so dangerous to shoot military in civilian chambers I would imagine the manufacturers are lending themselves to horrendous liability which I personally don't believe they would do. Is this ,to paraphrase Shakspeare 'much ado about nothing'?

quote:

Originally posted by Samuel_Hoggson:

quote:

Originally posted by k-22hornet:
Have you ever sent a few of the NATO-spec M855 or M193 cartridges to a pressure proof house?

No, but if I could get my hands on some properly stored VN era M193 and some current issue M855 I'd be tempted to compare them to domestic boxed "5.56" 55s and 62s.

Few realize just how difficult it is for civilians to get their hands on US M193 or M855, ie., first tier. Most of what we get by way of bulk purchases is from other countries. If from the US it is 2nd or 3rd tier (ie., rejects). Pressure data might not correspond.

Sam

Sam,
I too appreciate you adding to my knowledge base...thank you! Sorry if I came across as unappreciative.

quote:

Originally posted by zimbabwe:
If it is so dangerous to shoot military in civilian chambers I would imagine the manufacturers are lending themselves to horrendous liability which I personally don't believe they would do. Is this ,to paraphrase Shakspeare 'much ado about nothing'?

The reason most AR/AR bbl makers have, of late, abandoned .223 SAAMI dimensions.......even when they stamp .223 on the bbl.......is so they don't incur "horrendous liability" if someone has a problem running 5.56 NATO-spec ammo through it.

As to the RRA Wylde dimensions, you probably know it is something of a hybrid - generally considered safe with NATO-spec, yet purporting to give better accuracy. JMHO, but I don't see the point. If I want something to handle 2-3 MOA M193 and M855 I'll take my Colt 5.56 uppers. If I want something to drive tacks ....well, I don't want a compromise chamber.

Liability is lessened overall due to 1) the general non-availability of true NATO-spec ammunition and, 2) due to the safety margins of modern barrel steels. This does not mean SAAMI are just sissies for advising us not to shoot 5.56 in a factual .223 chamber.

Sam

The abundance of 223 ish chambers is an off shoot of several interests. Wylde, one of the most popular chambers other than 556 N or 223Rrem, is specifically designed for the AR, and is a chamber that has a shorter freebore than the 556, and a shallower leade angle than the 223, so it shoots both mag length and long seated loads with aplomb. Most High Power 223s are of this variety, and while HP is not tack driving by any means, it does require sub minute accuracy to perfrom on the the X rings of HP targets (1 MOA in diameter at 200, 300 and 600 yards).

Other chambers, such as the 223 AMU, 556 Compass lake etc, are designed with longer freebores and shallow leades to accommodate 80 or 90 grain 224 dia bullets for the lonmger lines (600 +) and are used extensively by those who shoot both match rifles and service rifles acroos the course and at long range (beyond 600, to 1000 yards).

I have a 223 AMU on an Ar15A2 service rifle that shoots 75/77 grain mag length bullets very well and has a freebore that allows seating 80 grain bullets to 2.600 (after 3500 rounds), and enables me to use a stiff charge that allows those 80s to exceed 2800 fps from that 20 inch badger barrel with no signs of excess pressure.

As far as the original question concerning 223 and 556 Nato ammo and safety, I would consider the chamber in my rifle as the crucial aspect of the issue. if the gun is marked 223 Rem., then I would assume it has a 1-12 twist and not a candidate for heavy bullets, say past 68/69s. If it is marked 556, then it likely has a faster twist (1-9 to 1-7) and is potentially not too effective with lighter bullets, espc. if the twist is 7, as light varmint bullets tend to often disintegrate.

The issue in my mind is mostly efficency in nature, pressure being secondary as long as you know what chamber/ammo combination your are using.

As far as the concern over what M193 or 855 is actually functioning at, one must assume the pressure is greater than 55k psi and use it accordingly.

556 M193 fired in 223 rem chambers can produce spikes up to 75k psi according to some data I have seen.

quote:

Originally posted by HPMaster:
556 M193 fired in 223 rem chambers can produce spikes up to 75k psi according to some data I have seen.

Good post. I had read that, too, but can't remember the source.

Agree that knowing your "chamber/ammo combination" is important. Colt M16A1 (small front pin) uppers are stamped 1:12. Parts kits will sometimes be encountered with barrels so marked by Colt or other maker, and sometimes with no markings whatsoever (I have one like that). They are almost invariably contract chrome-lined "pencil" type A1s w/1:12. All will handle M193 and are safe, if inaccurate, with M855.

I don't own a semi-only SP1 rifle or carbine at this time. IIRC, they were all 1:12s. Lower receivers were marked .223 (at least on the early ones). I doubt Colt altered chamber/throat dimensions specifically for the SP1s. I would not fret about M193 through these.

Similarly, preban Daewoos are stamped 5.56. The post-ban DR200s are stamped .223 (on lower receiver) and, interestingly, have a "retro" 1:12ish twist. If I had to guess, I'd believe them safe with M193. Problem is that I don't know this to a certainty.

The foregoing is to explain how, over time, the 5.56/.223 issue has become just as clear as mud.....and why the best advice we can give on an internet forum is conservative: heed SAAMI's position.

Pls note HPMaster's comment quoted above!

Sam

What a great thread! My thanks to all.
Peter.

quote:

Originally posted by ledvm:
So...a 5.56 X 45 with a 55 grain bullet should do fine in a .223 Rem bolt action rifle that shoots 55 gr bullets fine???

I had a lot of failures-to-fire putting 5.65x45mm in a .223/20-gauge Savage 24V.

quote:

Originally posted by TomP:

quote:

Originally posted by ledvm:
So...a 5.56 X 45 with a 55 grain bullet should do fine in a .223 Rem bolt action rifle that shoots 55 gr bullets fine???

I had a lot of failures-to-fire putting 5.65x45mm in a .223/20-gauge Savage 24V.

You should check the headspace, and impact on the primer. The chambers are too close to the same for misfires to be blamed on 5.56 instead of .223. Look at the picture ledvm posted for me. Maybe cerrosafe the chamber yourself first.

quote:

Originally posted by BigNate:

quote:

Originally posted by TomP:

quote:

Originally posted by ledvm:
So...a 5.56 X 45 with a 55 grain bullet should do fine in a .223 Rem bolt action rifle that shoots 55 gr bullets fine???

I had a lot of failures-to-fire putting 5.65x45mm in a .223/20-gauge Savage 24V.

You should check the headspace, and impact on the primer. The chambers are too close to the same for misfires to be blamed on 5.56 instead of .223. Look at the picture ledvm posted for me. Maybe cerrosafe the chamber yourself first.

It may have been a problem with headspace or throating. I had the Savage rebored, now it's a 6x45mm. It's legal for antelope and sage grouse, and there aren't any more misfires.

quote:

Originally posted by TomP:
I had a lot of failures-to-fire putting 5.65x45mm in a .223/20-gauge Savage 24V.

Primer cup hardness, probably. My RSA M193 will sometimes fail in one of my shorty uppers with a slightly worn pin.

Ezell and Stevens go into the whole M16 floating firing pin/light hits issue in detail.

Back when I was less careful about this particular issue I wondered why the Norinco would FTFire in the little Ruger bolt gun.

Sam