223 Rem vs 5.56 mm - Pistolsmith

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Old 09-20-2004, 06:48 AM   #1
Join Date: Dec 2003
Posts: 19
223 Rem vs 5.56 mm

I'm new to the whole AR 15 thing. I've always seen ammo sold as 223 (5.56mm). Now, my AR has 5.56 stamped on the barrel, and talking to some of my shooting buddies, they tell me that the 2 rounds (commercial 223 & 5.56 mm) aren't interchangable because of head space issues. Also, the reloading info I've found only says 223, not 5.56. I've compared 2 pieces of brass, and by looking, the shoulders of the 5.56 are sharper than the 223. Can anyone clearify this issue for me.
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Old 09-20-2004, 11:07 AM   #2
Join Date: Feb 2003
Posts: 16
.223 Remington vs. 5.56X45 NATO

Military specification chamber and throat dimensions for (5.56X45 NATO)firearms have slightly different dimensions in the chamber and throat as compared to the civilian, SAAMI specification
.223 Remington chambers. Also the NATO specification brass case
has slightly less internal volume than the
commercial .223 Remington brass case.

For guidance, SAAMI recommended in 1979 that 5.56X45 NATO military ammunition not
be fired in commercial .223 Remington sporting rifles, due to
the possibility of excessive chamber pressures resulting from the
chamber and throat differences.

As far as firing commercial .223 Remington ammunition in a firearm
stamped 5.56 NATO, there is no problem. However, when reloading
military brass, reduced loads are recommended due to the reduced
internal volume of military cases as compared to commercial cases.
Old 09-22-2004, 11:28 AM   #3
Join Date: Mar 2003
Posts: 64
Here are a couple of links you may find of interest:


Old 09-22-2004, 03:23 PM   #4
Join Date: Dec 2003
Posts: 19
thanks for the info & help..
Old 10-14-2004, 05:35 AM   #5
Join Date: Oct 2004
Posts: 104
Military is also loaded to higher pressure than commercial. Chambers in guns marked 5.56 are slightly longer and the shoulder is blown out to fire form in the military case. this is done to insure chambering in another wise dirty (at least more than normal under heavy use) full auto situation. Some manufacters will not honor their warranties in the chamber has been swollen by a military round -Sako
Old 10-16-2004, 09:48 AM   #6
Join Date: Apr 2004
Posts: 80
I don't know about any other makers, but Ruger has stated categorically that their Mini-14's are capable of handling any 5.56 ammo, even if it does say .223 on the gun. Given that they build in an extra margin of strength in their guns, I wouldn't doubt that a bit. Of course, safety is rarely an issue with the Mini-14. Accuracy, on the other hand...... :roll:

Old 04-10-2007, 06:12 AM   #7
Join Date: May 2002
Posts: 248
5.56 vs .223

The 5.56 does have a slightly longer case (most of the time) and thicker brass. In factory ammo it will not make much difference but, if you reload it will. The 5.56 brass MUST be trimmed after full length sizing. I saw a Colt A3 carbine blown up from careless reloading. Military 5.56 case, powder at max, untrimmed brass. The upper came apart, the mag was blown out, the barrel extension was cracked, the extractor spring buffer was blown through the back of the bolt, and the case was frozen in the chamber. It eventually went back to Colt and they estimated the pressure peaked at or above 100,000 psi. They intentionally blow up guns and measure the pressure and they had never seen one blown up that badly. Luckily, no serious injuries.

The two are interchangable, kind of.
Old 12-19-2013, 08:26 PM   #8
Junior Member
Join Date: Nov 2013
Location: Littleton, Colorado
Posts: 13
I've got several AR's in 5.56 and have shot thousands of rounds of .223 Rem with no problems. Not sure about the reloading.
Old 02-20-2014, 06:33 PM   #9
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Join Date: Feb 2014
Location: Pittsburgh
Posts: 49
Wow that's extreme. Hope no one was injured.
Old 03-12-2015, 04:48 PM   #10
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Join Date: Feb 2015
Location: USA
Posts: 1
I would also recommend that you get your barrel throat checked to make sure that it is a true 556 I have seen some barrels marked 556 that test is 223

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