Which Ammo? Chambered in .223/5.56 x 45 mm NATO

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First things first... This is a pathetic question and only one a complete idiot or noob would ask... I'm one of the two, potentially both...

Now that that is out of the way...

Which ammo should I be looking for? The AR15 is chambered in .223/5.56 x 45 mm NATO. Are these two rounds exactly the same? I've seen some online retailers advertise a .223 Remington category and the 5.56 NATO separately. Given the ammo prices, I really don't want to buy the wrong stuff.
The barrel in the rifle is a stainless steel match grade with a 1:8 twist.

So maybe the way to ask this question and look like less of an idiot would be to say...

I'm looking for the best ammo for plinking for my AR15 that is chambered in .223/5.56 x 45MM NATO. The barrel is a 1:8 twist. Any advice?
 
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.
Check the lower receiver for the exact chamber.
If it is 5.56 then you're OK to shoot both.
However if it is marked as .223 do not shoot 5.56 out of it.

55 grain is your normal cheaper option and fine for practice.
Arent you backwards on that ....as long as barrel or upper is chambered for 5.56 both are fine but if it says .223 then only .223 out of that barrel.If I am wrong how would lower even know what ammo is in chamber?
 
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Is the barrel marked 5.56? .223 has a shorter leade (the area in the chamber before it contacts the rifling) and can be more accurate but using hot 5.56 ammo can cause a pressure spike.
If it's 1:8 I'd bet it's 5.56 since .223 ammo is usually using lighter bullets (<55gr) and doesn't require that aggressive of a twist rate, more like 1:10 or 1:12. You should be good up to 78gr or so but in the upper end of that spectrum you'll need to test the ammo to make sure it works in your rifle.
 
.223 and 5.56 are NOT the same.
Check the lower receiver for the exact chamber.
If it is 5.56 then you're OK to shoot both.
However if it is marked as .223 do not shoot 5.56 out of it.

55 grain is your normal cheaper option and fine for practice.
While this normally makes sense in the case of the AR it is a POOR choice. There are so many AR's in so many calibers the only RELIABLE way to tell the caliber of an AR is what is stamped on the barrel.
 
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Where is it normally stamped on a barrel? Under the handguard? :confused:

I know you're not supposed to shoot 5.56 in a gun marked .223, but I wonder really how dangerous it is. We're not talking "blowing up the gun" dangerous, are we? It's hard to imagine a bolt gun having trouble with it...

BTW if the gun is marked ".223 Wylde", then both kinds of ammo are supposed to work. Just to add confusion to the picture!
 
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The 223 Wylde is a hybrid .223/5.56 chamber that should be able to use either type of ammo. The chamber is a mix of the two chambers that should give you a wider range of ammo loads that it can safely use. It's not a SAAMI spec chamber so if you start reloading it's best to ask your barrel maker to cut you a set of reloading dies or recommend a type to buy. The chamber can be best called a Wildcat chamber that is widely used. Like some US made 7.62X51mm NATO rifles have 308 chambers. o_O
 
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I know you're not supposed to shoot 5.56 in a gun marked .223, but I wonder really how dangerous it is. We're not talking "blowing up the gun" dangerous, are we? It's hard to imagine a bolt gun having trouble with it...
5.56 has thicker brass so to make up for it, faster powder is used. This results in higher chamber pressure. So yes you run that risk. Might be rare, and the gun blowing up could be the result of something else, but its possible.
 
I know this is a necro-thread, but since it's an important issue because AR15 platform rifles are so ubiquitous I'll just point out for the benefit of any lurkers around here that are trying to learn something...

I own a Colt AR15A2 Sporter-II that is marked ".223 Remington" on the lower receiver, yet the barrel between the flash hider and front sight post is stamped "CL MP 5.56 NATO 1/7". That means it's chambered for 5.56 NATO ammo (safe to also shoot .223Rem), "MP" (sometimes it'll say "MPI") means the barrel was tested for (internal/external) flaws using the "Magnetic Particle Inspection" method, and the "CL" means the bore is Chrome Lined.

Go with what's stamped on the barrel, as shown in post #17 ;)
 

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