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And as for 5.56mm vs. .223, the 5.56mm has a longer leade (throat).

The 5.56mm is also loaded to higher pressures.

So....

If you fire 5.56mm ammo in a .223 chamber, pressures will rise rapidly. Firing hotter ammo in a tighter chamber will do that. SAAMI considers it unsafe to fire 5.56mm ammo in a .223 chamber.

But it is safe to fire .223 ammo in a 5.56mm chamber.


Mad.
 

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If that ammo is marked, "5.56mm", do not shoot it in a .223 chamber. If the ammo is labelled ".223", then you can shoot it in either a .223 or a 5.56mm chamber.

In 1978, SAAMI issued a warning about using 5.56mm in a .223 chamber. They went so far as to call it "an unsafe combination".

See: http://www.saami.org

If you are thinking about getting an AR-15, get one with a 5.56 chamber. Bushmaster, Colt and RRA, (among others) are all available with 5.56 chambers.

Mad.
 

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Actually, AR barrels can be had with either chambers. So when you buy an AR, be careful to get the chamber that you really want.

All Bushmaster chrome lined barrels have 5.56 chambers. But their stainless barrels are reamed for .223.

Rock River Arms chrome lined barrels have the 5.56 chamber, but some of their barrels have the Wylde chamber or the .223 chamber. The Wylde chamber is a chamber with a throat longer than .223 but shorter than 5.56mm. Apparently you can use 5.56 and .223 in a Wylde chamber. Mr. Wylde was one of the early gunsmiths who accurized the AR back in the mid 80s.

This whole confusion over 5.56 and .223 is why you ought to only buy quality parts from an experienced dealer. That's the only way you can ever be truly sure what you are getting. If you buy a 5.56 barrel from Joe Schmoe, you may find yourself getting a .223 instead.

And there is nothing wrong with a .223 chamber as long as you only use .223 in it.


Mad.
 
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