.223 Rem VS 5.56mm
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.

Excerpted from people who know these things...

Just for curiosity,how does a person from Indiana claim the name Doctor Chicago?[:\]

I think it's a play on "Doctor Zhivago". but he might be from Gary, IN which is for all practical intents and purposes a Chicago 'burb.

Noah

Exactly

I originally lived in Downtown Chicago and moved out to Indiana so I could have Handguns, Conceal Carry, and Full Auto Machine Guns.
I like the city just not the gun laws.
I am there everyday for work.

You do know that all of this information is posted in the FAQ tacked at the top of this forum, right?

Yeah, and SAMMI says it's dangerous to shoot [b]9mm NATO[/b] in [b]9mm Para[/b] marked pistols too.  I guess someone should tell the Army and Marine Corps, 9mm NATO is all that's ever issued.

SAAMI is a product liability lawyer organization.  I'm actually surprised they allow anyone to shoot a firearm.

I'm still waiting for a documented case of damage or injury from shooting 5.56mm or 5.56mm NATO in a so-called .223 marked AR15 (or any other rifle).

-- Chuck

>>I'm still waiting for a documented case of damage or injury from shooting 5.56mm or 5.56mm NATO in a so-called .223 marked AR15 (or any other rifle).<<

Yeah, what he said............

Not to mention that most barrels from various factories these days are coming with "liability throats" that have mondo "jump" to the rifling.


I was actually relatively surprised when my AR10 was delivered with a remarkably short throat allowing me to seat out to the lands while staying at magazine length.


Then you should see the throat on my Remington 700 in 300WinMag, seating the bullets out almost another 3/16 of an inch further with my handloads to get them just off the lands when compared to factory loaded rounds like Gold Medal.


Similar happens with a lot of manufacturers these days, long throats unless you get into somewhat customized or rifles that are even more accuracy driven.

Yes it was just what the ammunition industry people were telling the law enforcement people in this country.  Just interesting

I was on the bushmaster website to check out what their rifles were chambered for. They list both .223 and 5.56. Which is it?

One more thing. So many of the AR15 owners shoot military ball through their rifles. Is there really a problem with this? Just a layman question I guess.