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View Full Version : WHY is 5.56mm different than .223 Remington?


Independent George
September 15, 2015, 11:06 AM
There's plenty of information on the the cartridge length, headspace, and chamber pressures - all useful stuff, but not what I'm interested in right now.

What I want to know is WHY there are two different chamberings of what is essentially the same round, and I haven't been able to find anything on it. Why did NATO standardize on 5.56 instead of the commercially available .223? Or, alternately, why didn't manufacturers converge on 5.56 when militaries were tooling up in that caliber? What benefit is there in having two different rounds that are essentially the same?

chris in va
September 15, 2015, 03:35 PM
I suspect it has to do with pressure and velocity. 5.56 has more of both, similar to the 9mm NATO.

jmr40
September 15, 2015, 04:46 PM
Before the internet they were the same and used interchangeably. In reality the 5.56 is a 223 that can be loaded a little hotter according to SAAMI specs and the military rifles have chambers cut a little looser to allow better reliability. The military chose the metric designation vs inches for civilian rifles. One thing to remember, just because the specs allow for more pressure in 5.56 does not mean all of it is loaded right to the max.

It is normally considered just fine to shoot 223 in guns marked as 5.56, but there is an extremely remote possibility one of the hotter 5.56 rounds combined with a very tight 223 chamber could be over pressure. Most of the time the worst thing that would happen is that a 223 chambered semi-auto would not function properly with 5.56 ammo. But 223 chambered semi's are quite unusual, most rifles marked as 223 are bolt guns.

A lot is made of this, but you can run into exactly the same issues with almost any chambering. Due to manufacturing tolerances there are no two 30-06 rifles with exactly the same chamber dimensions. There are at least 3 different pressure levels of 30-06 ammo that can be purchased on shelves not counting handloads. If you get the right combo of hotter loaded 30-06 ammo in a tighter chambered rifle you are just as likely to run into problems. Quite possibly more likely, and we don't have 2 different names for 30-06. Or any other round.

TMD
September 15, 2015, 04:54 PM
Before the internet they were the same and used interchangeably

^^^This^^^

RJay
September 15, 2015, 05:25 PM
the .308 and the 7.62X51 have different pressure levels and the SAAMI recommends not shooting the 7.62X51 in rifles marked only 308. The SAMMI does not issue the same warning in reference to the 5.56 and the .223, but as already been posted most military rifles chambered for the 5.56 are chambered larger for reliability. Some military 5.56 cartridges will chamber in the .223, some will not. Some 5.56 will not even chamber in the .223 or will " stick " and not extract. IIRC I remember that because I once made a blanket statement in reference to the above and was corrected.

mehavey
September 15, 2015, 05:32 PM
The 5.56 chamber has a longer throat and gentler lead-in to the lands than the 223REM chamber.
The pressures of the two cartridges, however, are arguable the same when measured by the
same equipment, the same methods, at the same location.
http://ballistictools.com/articles/5.56-vs-.223-myths-and-facts.php

briandg
September 15, 2015, 06:08 PM
To complicate it even further, ballistically, and generally dimensionally, the .222 rem mag are almost identical. This round was proposed to the military as the new round, and they requested that the round be tweaked. The .223 was created.

The .222 magnum was created in 58 and offered to armalite, and released commercially. The .223 was released in 63, and soon the .222 replaced in the hearts of american shooters.

a .223 is likely to rupture if fired in a .222 magnum chamber.

Darn wind
September 20, 2015, 09:33 PM
I wish I could quote post but, to the above. The 222 was designed in 1950 and if I recall correctly it was the first to be presented to the military as was the 222 magnum which were the predecessor to the 223. Also the AR 10 was the initial design and scaled back in 1957 to use the 223 if I recall correctly.