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Discussion Starter #1
Colt Match Target M4 Carbine

Lower is stamped .223 Cal.

Upper is stamped behind the muzzle break:

C MP
5.56 NATO 1/7


Wondering what this rifle is actually chambered for......?
 

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Discussion Starter #3
Well, there's a difference between 5.56 and 5.56 NATO.................just sayin'......the attached booklet says .223 Cal ammo.....still a bit confused.....I dunno.
 

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Unless it's an aftermarket barrel, for a definitive answer I'd ask Colt.
 

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Discussion Starter #5
They're little generic booklet says .223 Cal. ......but I'm thinkin' the chamber is what is stated on the Bbl. ..........I dunno.
1 in 7 twist is for the 5.56 NATO..........Stumped.
 

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Since the chamber is integral with the barrel, that should be the definitive data, however you are still left with the question, "Does 5.56 mean 5.56 NATO?" I'd think so but that's just a guess.
 

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isn't there some way to guage or measure for it?
 

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Of course there is, but you've got to have the tools; a chamber gauge, or lacking that, make a casting and measure it with calipers. I think a phone call or email would be easier.

[ Note that the specs for the 5.56 NATO round are set by the European agency CIP. ]
 

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I dont know why the barrel would have anything other than what its made for stamped on it.

What other 5.56 ammo is there other than 5.56 NATO?
 
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Saying 223, 5.56, and 5.56 NATO is like saying: Camaro, Mustang, Ford Mustang.

223 ammo is lower pressure ammo and should be the only ammo used in a barrel marked ".223". A barrel marked 5.56 is designed to handle a higher pressure cartridge than the .223 Remington, but can also shoot the .223 Remington cartridges. The 5.56 has a different chamber specification than .223 Remington. There is a third variation called a .223 Wylde chamber that can shoot both rounds safely, but IIRC the Wylde barrels are still marked 5.56.

The barrel is what determines which round the chamber is cut for. The lower receiver can say "Squishy Bananas" but unless it is clearly marked as something other than 223 or 5.56 - such as 9mm, .308, or one of the other non-223 sized cartridges, it will handle .223, 556mm, 6.8 SPC, 300 BLK, 6.5 Grendel, or any one of a host of others. There are some charts for this available over on ArfCom (AR-15.com). It can get pretty confusing if you move away from 223/5.56 so it is best to check what components are compatible.

I guess I should answer your question directly: Always go by the marking on the barrel. The lower marking is generally meaningless. Most Colts use 5.56 barrels. Ones that don't should be clearly marked - on the barrel itself.
 

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Discussion Starter #11
The barrel is stamped as I show it in the OP.......5.56 NATO 1/7 .....right behind the muzzle break.
 

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Sorry, I must have misread your OP. As others have said, 5.56 NATO on the Barrel indicates what that barrel is chambered for and it will safely fire the .223 Remington cartridge.
 
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A 556 stamped barrel dictates it's properly chambered for 556 nato. The lower is only representing what can be fed though the magazine well. If someone told you there was a difference between 556 and 556 nato, then they lied. 556x45 is 556 nato.

As you probably already know, it's perfectly safe to utilize .223 Remington in a 556x45 chambering. Your good to go. If you want to call Colt and get a definitive answer, then go for it for peace of mind.

I do love a nice Colt! Wouldn't mind some pics...:image035:
 
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