5.56 vs .223 pressures

I'm having a devil of a time srcounging up this information. I think SAAMI changed their website and I have not been able to figure out where this info is located.
I have read several threads on 5.56 vs .223, but have not been able to find an authoritative source on the difference in pressures between the two rounds. I have found folks saying they differed by so much, etc. but without citing any documentation, such as a reloading manual or SAAMI. (They very well may be right, but I prefer solid documentation.)
Basically what I am wanting to know is if anyone has a link to the safely allowable range of pressures (in p.s.i.) for a .223 chamber and the same information for a 5.56 chamber from an authorative source.
Thanks in advance.
PS I should add that the reason I need the information is because I am arguing with someone about how safe it is to fire 5.56 in a .223 chamber and they are insisting that there is no difference between the two rounds. I have told him that there are higher pressures in the 5.56 round and that this is what makes it unasfe to fire 5.56 in a .223 chamber. I need some "proof" to convince him. If it was just some Joe Schmoe, I wouldn't care if they were being blockheaded, but this is a family member, so I have more of a stake in convincing them.

Look at page 7 of the SAAMI technical data sheet unsafe firearm-ammunition combinations. It doesn’t have the data you are looking for but it clearly states not to use 5.56mm in a .223
http://www.saami.org/specifications_...mbinations.pdf

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Originally Posted by 5pins

Look at page 7 of the SAAMI technical data sheet unsafe firearm-ammunition combinations. It doesn’t have the data you are looking for but it clearly states not to use 5.56mm in a .223
http://www.saami.org/specifications_...mbinations.pdf

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Yeah, I saw that and it's good info, but I still want to find the actual pressure info too.
Thanks.

It's difficult to make a direct comparison of SAAMI 223 Remington pressures and mil-spec 5.56mm pressures because different methods are used to measure the pressures of the two cartrdiges. However, Ned Christiansen has posted some very interesting data on the subject:

". . . As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. . ."

Since the SAAMI MAP for the 223 Remington is 55,000 PSI, that puts XM193 fired from a minimum spec .223 Remington chamber at 17,550 PSI over the SAAMI MAP.

Here is some reading that should help. The Hornady link lists the pressures of the .223 and 5.56.

http://www.hornadyle.com/faq/index.php?qIdx=3
http://le.atk.com/pdf/223VS556.pdf
http://ammo.ar15.com/ammo/project/hist_diff.html
http://www.cheaperthandirt.com/Media...px?mediaid=316

Thanks for the info. It helps and I appreciate it.

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Originally Posted by 5pins

The Hornady link lists the pressures of the .223 and 5.56.

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Unfortunately, those pressures were obtained using different methods, so they are not an apples to apples comparison.

In my mis-spent youth I reloaded some 5.56 hot enough to drop primers.


Has he shot any 5:56 in his 223? I would like to read the one fired brass and see if is a problem for him in his gun.


If this is a theoretical discussion, he might be right depending on the manufacturer. Some makers are making one load and putting different lables on it.

The newer Ruger Mini-14's, except for the target version, are chambered for 5.56, and I believe it says .223 on the rifle. The manual also states both 5.56 and .223 can be fired from this gun. I’m about to purchase one, and I already have a stockpile of both .223 and 5.56.

What I’ve heard is that if your rifle is chambered for 5.56, you can shoot .223. However, if your rifle is chambered in .223, you should check with the manufacture, or your manual before firing 5.56. Not all .223's can safely fire 5.56.

NATO cartridges are loaded 10% more pressure than standard loads, but since there is a slight difference in the .223 case and the 5.56 case, there might not be a direct comparison available.

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Originally Posted by wingspar

NATO cartridges are loaded 10% more pressure than standard loads,

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The pressures of SAAMI rounds and NATO rounds are measured using different methods. Therefore your "10%" figure has no merit.

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Originally Posted by wingspar

but since there is a slight difference in the .223 case and the 5.56 case

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There is no significant difference between 5.56mm cases and common commercial .223 cases and therefore the cases are a non-issue in the difference in pressures between the two systems. The chamber and specifically the free-bore and leade are where the significant difference lies.

http://www.box.net/shared/static/j4py5ig0v9.jpg

5.56mm NATO versus 223 Remington Chamber Differences

A SAAMI spec .223 Remington chamber will have a shorter leade with a sharper angle to the leade and a shorter amount of effective freebore than a 5.56mm NATO chamber. The freebore itself will also be narrower in the .223 Remington chamber.


http://www.box.net/shared/static/oobedcsfkc.jpg

raw pics courtesy of Ned Christiansen



With all other things being equal, the 5.56mm NATO chamber with its longer and shallower angled leade and longer amount of effective freebore will produce less chamber pressure than a .223 Remington chamber, when firing .223 Remington SAAMI Spec ammunition. Because of this, 5.56mm NATO amunition can be loaded to a pressure that would be considered excessive in a .223 Remington chamber, yet acceptable in a 5.56mm NATO chamber. (Pressures are measured using different methods between the two systems.)


The leade of a SAAMI 223 Remington chamber.

http://www.box.net/shared/static/rngqlofqpr.jpg




http://www.box.net/shared/static/0l86by3ps2.jpg
from Rifle magazine



The official SAAMI 223 Remington drawing.

http://www.box.net/shared/static/kohxuqcxcp.jpg


From Jeff Hoffman, co-owner of Black Hills Ammunition

“The 5.56 IS a higher pressure/velocity cartridge, but it is made to a military standard, with different test methods, (and therefore is not easily directly comparable to .223 pressures) . . . the general spec for US 5.56 ammo is 58,700 psi max, measured at case mouth. . . Please note this is a different method than SAAMI transducer or copper crusher, as used on commercial ammunition. 5.56 ammunition spec results in ammunition loaded to a higher pressure level than commercial .223, but the test methods specified are different . . .The spec calls for a different pressure test method than SAAMI spec ammo, and is not directly comparable . . . “



Here's a very interesting quote posted by Ned Christiansen on M4carbine.net:


". . . In short, you can safely fire all 5.56 AND 223 ammunition in a gun properly chambered for 5.56. You MUST NOT fire 5.56 ammunition in a 223 rifle. As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. . ."

Since the SAAMI MAP for the .223 Remington is 55,000 PSI, that puts XM193 fired from a minimum spec .223 Remington chamber at 17,550 PSI over the maximum.





(The following is just a generalization to demonstrate the concept. DO NOT hold me to the exact numbers as they are not correct and they ignore the difference due to the different methods used to measure chamber pressure.)

Consider the left graph pictured below; M193 fired in a 5.56mm chamber. The pressure is within the MAP limit. Now, take the exact same round, (same powder, same charge of powder) and fire it from a .223 Remington chamber; pictured in the right graph below.

Because the .223 Remington chamber has a shorter and sharper angled leade compared to the 5.56mm chamber as well as a shorter effective free-bore, the bullet engages the rifling sooner in the .223 chamber than it would have in a 5.56mm chamber. This causes the pressure to rise faster, peak sooner and reach a higher (and per SAAMI, unsafe) level than it would have if the round had been fired from a 5.56mm chamber.


http://www.box.net/shared/static/l8z8skqkok.jpg



Many people seem to incorrectly believe that 5.56mm brass cases have significantly reduced case capacity compared to .223 Remington cases. The table of case capacities shown below demonstrates that this notion is false.

http://www.box.net/shared/static/eeig0a9r3c.jpg



http://www.box.net/shared/static/3i5hgvf18u.jpg



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Originally Posted by Molon

The pressures of SAAMI rounds and NATO rounds are measured using different methods. Therefore your "10%" figure has no merit.

There is no significant difference between 5.56mm cases and common commercial .223 cases and therefore the cases are a non-issue in the difference in pressures between the two systems. The chamber and specifically the free-bore and leade are where the significant difference lies.

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Well, I figured I’d get whacked for my post, but I am in a learning stage when it comes to .223 and 5.56. The 10% higher pressure came from a discussion on 9mm, and may not even apply to the .223 and 5.56, and of course, I did not bookmark the link, which was either on the SAAMI or NATO page, and I’ve never been able to locate that again, and I’ve tried several times. I stand corrected

I did find this info tho.

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Originally Posted by Molon

5.56mm NATO versus 223 Remington Chamber DifferencesFrom Jeff Hoffman, co-owner of Black Hills Ammunition

“The 5.56 IS a higher pressure/velocity cartridge, but it is made to a military standard, with different test methods, (and therefore is not easily directly comparable to .223 pressures) . . . the general spec for US 5.56 ammo is 58,700 psi max, measured at case mouth. . . Please note this is a different method than SAAMI transducer or copper crusher, as used on commercial ammunition. 5.56 ammunition spec results in ammunition loaded to a higher pressure level than commercial .223, but the test methods specified are different . . .The spec calls for a different pressure test method than SAAMI spec ammo, and is not directly comparable . . . “.....

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Thank you. While just an observer in this information exchange your continued reference to "different test methods" with no further explanation left me with a "not in front of the children" feeling. It all makes sense now. :)

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Originally Posted by RWBlue

In my mis-spent youth I reloaded some 5.56 hot enough to drop primers.


Has he shot any 5:56 in his 223? I would like to read the one fired brass and see if is a problem for him in his gun.


If this is a theoretical discussion, he might be right depending on the manufacturer. Some makers are making one load and putting different lables on it.

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This is theoretical. I don't think he's ever actually fired 5.56 in his rifle.

Thanks all for the outstanding information. This has been very informative and will definitely help me pick my hombre up by the stacking swivel and smack him down to parade rest, so to speak. :D

Wow Molon! Great post as always :)

I know the differences, but your post is so well illustrated that needs to be a sticky.

Like I said earlier, I’m new to these cartridges, and am trying to learn, even tho I might sound like I’m trying to seem like I know what I’m talking about.

I had the camera out this morning, and decided to photograph a 5.56 and a .223 side by side. Not sure I can see a difference, and decided not to post any of the photos, but just now in looking at them, I notice the lack of NATO on the 5.56 box. I was assuming all 5.56 ammo was NATO, but now, I have the question. Is all 5.56 ammo NATO, or is some of it not?

The photo. The photo. What causes the discoloration in the 5.56 brass? (The one on the left)

http://www.pbase.com/wingspar/image/...8/original.jpg

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What causes the discoloration in the 5.56 brass? (

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Annealing.. Perfectly normal, mainly a cosmetic thing.

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Originally Posted by Yute

Annealing.. Perfectly normal, mainly a cosmetic thing.

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Thanks. I see that a lot, but it isn’t consistent between brands.

On my question on whether 5.56 is always NATO, or is there a civilian 5.56 load? I noticed that it does not say NATO on my box of 5.56.

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Originally Posted by wingspar

On my question on whether 5.56 is always NATO, or is there a civilian 5.56 load? I noticed that it does not say NATO on my box of 5.56.

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This is just a guess here, so don't take it as the 100% truth. 5.56 is a standard for ammo. The NATO stamp certifies that it was made to 5.56 standards in a NATO approved facility. For example, I have some IMI M193 (same as Winchester Q3131A). It's marked 5.56 like your picture, but is not marked with the NATO stamp. I also have some Federal XM193 (marked LC 08) that has the NATO stamp. My guess is that it's marked with the stamp because of the facility that it was manufactured in and the standard it was made to.

I will probably show my newbieness here, but that’s ok. I’m hear to learn, not to share knowledge, at least on this cartridge. 5.56 may be a standard for ammo, but what I’m wondering is if 5.56 is always loaded to NATO pressures, or are some 5.56 cartridges loaded to SAAMI standards. In other words, similar pressures as the .223 cartridge if the box and cartridge are not marked NATO.

I know the difference between 9mm and 9mm NATO. I’m just wondering if the same applies to the 5.56 cartridge. No amount of Googling on the subject got me any cut and dry answers.