What is the difference between a .223 and a 5.45 caliber AR15?  I thought the were the same, but the chart at the top of this discussion lists them seperately by manufacturer. And what exactly is a Wylde .223?

Thanks (obvious n00bie)

Do you mean what's the difference between the .223 and the 5.56x45? If so, the 5.56 burns hotter creating higher chamber pressures. There are a few more differences, but I can't remember them right now.

Well this I know:

You can shoot both (.223 & 5.56) in a rifle that is stamped 5.56.  That rifle is chambered to take the extra firepower.

You should not shoot 5.56 in a rifle that is stamped .223.  That rifle's tolerances are lower, and you run the risk of damage to the rifle, and possibly yourself.

Most AR's are 5.56.  I wouldn't buy one that wasn't.

five2one:

This site should answer everything.

http://www.ammo-oracle.com/#diff

On the barrel of my AR is stamped 5.56*45, but on the lower reciver is stamped .223. What does it mean?

5.54x39mm is the Russian caliber - as in AK74

on any weapon the way the barrel is stamped is what cal that you use. on the ar15 the lower rec stamped .223 does not mean didly, that the barrel stamped 5.56 means the barrel is chamberd in 5.56. so you can use both .223 or 5.56. the lower has nothing to do with calibur because you can use anything from a 9mm to a 50BMG conversions. the reason you cannot use a 5.56 in a .223 is the .223's chamber throat is tighter.

Crohunter, Thank you for the tip on the great site. Never again will I say that 5.56x45 is the same as .223 Remington.

Thanks to everyone else too.

Check this out.  I recently bought a OLYARMS PCR-4 and this is what they wrote on their website.

CALIBER
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First off, every barrel is stamped with the caliber. Since we make over 10 different calibers that are interchangeable on any standard Olympic (or mil any spec) .223 caliber lower, this should be the first thing you check.  The standard .223 caliber rifles are marked "5.56", while the alternative calibers are marked appropriately (45ACP, 40 S&W, 6 PPC, 17 Rem. etc.).
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It's a little hard to tell if the rifle is chambered for 5.56 or .223.   I'll have to call them unless someone can untangle this for me.