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Old November 12, 2012, 09:09 AM   #1
CS86
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.223 & 5.56x45 confusion

I've had some confusion on the 2 calibers listed in the title. Awhile back I thought there was a slight dimensional difference between the 2. I've reciently started looking at both of them again, and they have the exact same outer dimensions. I thought that you couldn't shoot a 5.56 in a .223 but you could the other way around. Why can't you shoot a 5.56 in a .223 if the outer dimensions are the same?
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Old November 12, 2012, 09:21 AM   #2
CrustyFN
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Because the 5.56 is a higher pressure round.
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Old November 12, 2012, 09:59 AM   #3
CS86
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Does the 5.56 hold a higher volumn of powder?
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Old November 12, 2012, 10:41 AM   #4
JimDandy
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The simplistic answer that doesn't say much more than "Because I told you so" is that SAAMI has found shooting 5.56 in a .223 chamber to be dangerous. The case walls of 5.56 NATO are, from what I hear, thicker which ups the pressure. While the brass may be the same on the outside, in addition to the thickness being different, according to my Hornady book, the Maximum C.O.L. for the .223 is very slightly longer.

From a search on the internet on a site called The High Road:

Quote:
223 ammo is OK in 5.56 barrel.

5.56 ammo is not OK in .223 barrel.

This was reported in the American Rifleman magazine recently.

.223 chamber is "smaller" than 5.56 chamber.

http://i227.photobucket.com/albums/d...comparison.gif

.223 Remington vs. 5.56: What’s In a Name


[/quote]

I assume some of those phrases are webpage titles, so websearching them may provide more info.
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Old November 12, 2012, 10:59 AM   #5
rg1
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The main difference is the chambers of .223/5.56 rifles. The 5.56 chamber has more freebore than does standard .223 chambers.
http://ar15barrels.com/data/223-556.pdf
This allows longer nato rounds to chamber without jamming into the rifling of the barrel plus the freebore reduces initial chamber pressure.
The cases of 5.56 brass are the same dimensions as standard .223 brass with some or a lot of military cases even lighter than commercial .223 brass.
Scroll down in this good article to see some weight samples of .223/5.56 brass.
http://www.6mmbr.com/223rem.html
It's been written that 5.56 chamber pressure maximum is 58740 psi while .223 commercial pressures are limited to 55000 psi. Doesn't mean that all ammo whether military or civilian is loaded to these pressures though.
Another good article:http://weaponsman.com/?p=604

Last edited by rg1; November 12, 2012 at 11:18 AM.
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Old November 12, 2012, 12:12 PM   #6
higgite
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Check out this article from the 2013 Gun Digest:

http://cheaperthandirt.com/blog/?p=27893
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Old November 12, 2012, 12:54 PM   #7
comn-cents
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I tride shooting 556 in a Ruger target m77 chambered for .223 about 15 years ago and the bolt would not close.
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Old November 12, 2012, 04:37 PM   #8
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Quote:
I tride shooting 556 in a Ruger target m77 chambered for .223 about 15 years ago and the bolt would not close.
Two of my .223 rifles have Match chambers. Some .223 ammo will not chamber in those guns.

Volumes have been written about the dangers of firing 5.56mm ammunition in .223 chambers.

i've been weighing the cases of my accuracy reloads since since 1968. US made military 5.56mm cases are not thicker than commercial .223 cases.

With the wild popularity of the AR-15 and the proliferation of barrel makers; chambering of .223/5.56mm rifle barrels has gotten very sloppy. Some chambers are large while others are close to or smaller than SAAMI minimum for .223. I recently returned a barrel to a well known maker because the chamber was out of round. That happened because an unqualified person reamed the chamber.

Until recently few bothered with pressure testing of 5.56mm ammo fired in .223 chambers: They just bought the SAAMI line. That has now changed:


http://www.luckygunner.com/labs/5-56-vs-223/

Last edited by thallub; November 12, 2012 at 04:59 PM.
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Old November 12, 2012, 05:00 PM   #9
CS86
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Thanks for the posts. They gave me a much better understanding.
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Old November 12, 2012, 06:23 PM   #10
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I do not endorse this,but the fact remains. I know 4 National Guard members. Remington 223. Each have shot well over 1000 military rounds down their rifles with out so much as a one issue. The increase in pressure between the 2 is there for sure,but a far cry away from what modern rifles will handle. This is just what it is. Would i do it-Never Ever,
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Old November 12, 2012, 07:48 PM   #11
oldpapps
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CS86,

Quote:
"I've reciently started looking at both of them again".

Just load for the weapon.

Brass wise, they are so close to being the same, it matters not.

The chambers/throatings of the weapons are different. These differences can and will give pressure problems.

Push come to shove, shoot what you must but as a general rule, be nice to your weapon and use .223 Rems in your .223 Rem. The mix chambers and 5.56 will eat them all up.

Buying ammo? Buy what your weapon is marked as.
Loading your own? Just load for the weapon.

Be safe,

OSOK
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