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I thought all Colt’s were able to handle 5.56mm pressures. Is this not the case? This is on the model 6721 to be exact. Thanks for any response in advance.
 
Posts: 1285 | Registered: December 04, 2007Reply With QuoteReport This Post
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I'm not very knowledgable about AR's, but I don't think the lower has any determination of whether it can shoot only .223 or 5.56 also. I believe that's the barrel chamber on AR's.
 
Posts: 19817 | Registered: June 12, 2005Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
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quote:
Originally posted by jimmy123x:
I believe that's the barrel chamber on AR's.


I agree. And it isn't the chamber pressure that sometimes causes problems with shooting 5.56 in 223 chambers, it's the case and bullet seating. (As I understand it.)




“The fundamental cause of trouble in the world today is that the stupid are cocksure while the intelligent are full of doubt.”
— Bertrand Russell
 
Posts: 42075 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Factory Colt AR-15 barrels have always been chambered in 5.56 NATO regardless if they are marked .223 on the lower receiver. The difference between the two is in the throat of the chamber. 5.56 chambers have a longer throat than .223, which allegedly/potentially could cause an overpressure situation when shooting a hot 5.56 load in a tight .223 chamber. But there would not be any issue going the other way.
 
Posts: 1718 | Location: WI | Registered: December 29, 2012Reply With QuoteReport This Post
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Of course lower has nothing to do with it. I have not seen a colt barrel (real one) that wasn't marked 5.56. I'm sure given the history and volume they exist, but I've just never come across one. Mine is marked 5.56.


“So in war, the way is to avoid what is strong, and strike at what is weak.”
 
Posts: 8747 | Registered: October 14, 2004Reply With QuoteReport This Post
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I believe the Colt 6721 rifles have always had a lower marked .223. Total guess but this gun originated in the 1990s around the time of the federal and state assault rifle laws. Maybe Colt thought the HBAR and marking it .223 could help it avoid being banned because that made it seem more like a civilian sporting rifle.
 
Posts: 831 | Registered: September 27, 2008Reply With QuoteReport This Post
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The 6721 has a 556 NATO 16” 1/9 HBAR barrel. The lower, handguard and bcg have varied along the way. The coveted lower is the one that reads Tactical Carbine but even that one has a 223 marking on the lower.
 
Posts: 17 | Location: NM | Registered: May 30, 2020Reply With QuoteReport This Post
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6721 is a 5.56 chamber.


---------------------------------------------
"AND YEA THOUGH THE HINDUS SPEAK OF KARMA, I IMPLORE YOU...GIVE HER A BREAK, LORD". - Clark W. Griswald
 
Posts: 2074 | Location: The South | Registered: September 12, 2005Reply With QuoteReport This Post
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.223 and .222 caliber marked lowers are generally meant for the overseas market.

Italy and South Africa being an example

18Z50
 
Posts: 273 | Location: North Coast | Registered: October 31, 2010Reply With QuoteReport This Post
Military Arms Collector
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.223 is often used to make it sound less military like. Your rifle is capable of shooting either .223 or 5.56mm.
 
Posts: 10666 | Location: Orange County, CA, USA | Registered: March 18, 2003Reply With QuoteReport This Post
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quote:
Originally posted by Zero1911:
<snip>
The coveted lower is the one that reads Tactical Carbine but even that one has a 223 marking on the lower.

I can confirm that ...



However my M16 is stamped 5.56 on the receiver;
so I think its just the difference between a commercial and LEO/Military receivers


If you really want something you'll find a way ...
... if you don't you'll find an excuse.

I'm really not a "kid" anymore ... but I haven't grown up yet either Wink
 
Posts: 5264 | Registered: January 11, 2007Reply With QuoteReport This Post
MAGA
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'73 SP1



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Posts: 1402 | Location: Indiana | Registered: July 10, 2001Reply With QuoteReport This Post
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