RandyA

What is the difference? Or how much difference? I see many manufacturers selling AR 15's, either and not both, .223 or 5.56 NATO.[>:]

stalkingbear

Actually the main difference is bullet weight and rifling rate of twist.

mello_collins

They are different enough to cause you bodily harm. There was an excellent write up in Sep(?) America Rifleman. I found this write up on the web.

“There are a lot of questions about these two cartridges. Many people think they are identical - merely different designations for commercial and military. The truth is that, although somewhat similar, they are not the same and you should know the differences before buying either cartridge.

The cartridge casings for both calibers have basically the same length and exterior dimensions. The 5.56 round, loaded to Military Specification, typically has higher velocity and chamber pressure than the .223 Rem. The 5.56 cartridge case may have thicker walls, and a thicker head, for extra strength. This better contains the higher chamber pressure. However, a thicker case reduces powder capacity, which is of concern to the reloader. The 5.56mm and .223 Rem chambers are nearly identical. The difference is in the "Leade". Leade is defined as the portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. It is also more commonly known as the throat. Leade in a .223 Rem chamber is usually .085". In a 5.56mm chamber the leade is typically .162", or almost twice as much as in the 223 Rem chamber. You can fire .223 Rem cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity over firing the .223 round in the chamber with the shorter leade it was designed for.
Problems may occur when firing the higher-pressure 5.56mm cartridge in a .223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads and gun functioning issues.
The 5.56mm military cartridge fired in a .223 Rem chamber is considered by SAAMI (Small Arm and Ammunition Manufacturers Institute) to be an unsafe ammunition combination.
Before buying either of these two types of ammunition, always check your gun to find what caliber it is chambered for, then buy the appropriate ammunition. Most 5.56mm rounds made have full metal jacket bullets. Performance bullets - soft points, hollow points, Ballistic Silvertips, etc. - are loaded in .223 Rem cartridges. Firing a .223 Rem cartridge in a 5.56mm-chambered gun is safe and merely gives you slightly reduced velocity and accuracy. However we do not recommend, nor does SAAMI recommend, firing a 5.56mm cartridge in a gun chambered for the .223 Rem as the shorter leade can cause pressure-related problems.”

That is pretty much the same as the magazine.

mello

falcon

i've been firing 5.56mm cartridges in .223 rifles since i had my .222 Sako re-chambered in 1968. Have never had any problem at all in any ofthe .223 guns that i have owned. i have a cheap old Handi rifle in .223. This thing hasthe biggest sloppy chamber i have ever saw ina .223. It also just loves my TW 67 5.56mm ammo: It routinely shoots sub .5 inch groups at 100 yards. This despite the dire warning from NEF not to shoot 5.56mm ammo in that gun.

"The 5.56 cartridge case may have thicker walls, and a thicker head, for extra strength."

In factmany military cases weigh less than .223 cases.While re-loading for fine accuracy i haveweighed thousands of 5.56mmand .223cases.

Here is a good link to 5.56mm and .223 issues:

http://www.ar15barrels.com/tech.shtml

thndrchiken

The only real difference is that the 5.56 has thicker case walls which reduces case capacity. It is completely safe to use 5.56 data in a 223 case but not vice versa.

falcon

"The only real difference is that the 5.56 has thicker case walls which reduces case capacity."

Not necessarily so, see the link i posted. I have weighed thousands of cases and LC military cases are about as light as they get. These are the cases that i prefer for my accuracy loads.

RLoving1

The Seirra(sp) Reloading book has 2 different sets of load data,,,the 223 is more powder with same load...I'll stick with suggested AR data myself!I read the article in Amercan Rifleman,good read with lots of info.!

RandyA

Holy chit! This is complicated, I never thought there was any difference, until I was shopping for an AR, then seen the one for .223 and one for 5.56. When I buy I think I will buy the .223. Thanks for the input.

Now how about, which AR? Talk about choices!

RLoving1

5.56 and 1 in 7 twist! You can do whatever you want and shoot both!

HighDesertWolf

for now on I wont do it. but a few months back before I knew the actuall difference I fired a box of federal XM-193 5.56 through my savage 10fp in .223 I dont recall seeing signs or experiencing excessive pressure. Infact after finding out that its not a good idea to shoot 5.56 in a .223 chamber i went back and gave the 5.56 brass a thorough examination to each casing and everything was fine. I did have some more XM-193 and I measured the OAL dimension and it was 2.255" well within .223 specs. maybe I got lucky? but now with the new knowledge I wont do it again just incase.