Educate me, please! AR question

[PA45ACP]

Was looking on gunbroker tonight. At Colt 6520's and 6920's. Appeared 6520's are marked .223 on the lower, and 6920's are marked 5.56. I have never paid much attention to it, but I was curious if there was a difference. Are the lowers different? Do they recommend 223 in a 6520? What gives?

[The_War_Wagon]

According to Colt, the distinctive feature of the 6520 is... a 'pencil' barrel. It still has a 5.56 chamber and the pencil bbl is STILL a 5.56 bbl.

http://colt.com/law/ar15a2.asp

ta da.

[arjohnson]

Just differant roll marks, lowers are the same. Colt 6520 and 6920 both are chambered for 5.56, which means they will also shoot 223 without issue.

[Daycrawler]

5.56 military rounds will have a higher chamber pressure. .223 has a lower chamber pressure. Therfore you should go with the 5.56 as it will shoot both rounds. As for your choice in Colt I see nothing wrong at all with that.

[ScotsGuards]

The 6520 is a light 1/7 twist barreled AR-15A2. The A2 model has a fixed carrying handle/rear sight housing. The 6920 is a stepped M-4 profile 1/7 twist barreled AR-15A3 rifle. The A3 has a removable carrying handle/rear sight housing and a picatinny railed flattop upper receiver. Both are chambered for 5.56 NATO regardless of the receiver markings.

[Bravo Whiskey]

If you check the Colt web site you will find that the 6520 and the 6920 are the same except that the 65's upper has the milled carry handle and the 69's upper has a detatchable handle over a flat top. Both are Cambered for 5.56.

[Bravo Whiskey]

Also, Check out what you bid on GB. I have found good buys and have found misrepresented items as well.
If the barrel is stamped .223 I would doubt that it is a Colt 6520.
I almost was stuck w/ an "LMT" fake. Do your research and ask the seller ?'s.
Good luck
BW

[Daycrawler]

Op read up there is a diffrence! Just yesterday afternoon I was told that a guy had an AR blow up in his face. It was a told it was most likley from a squib load. He will be ok and was wearing safty glasses.

I pulled this from another site. I framed out the last paragraph in XXX if you take any thing from this it should be that!


http://www.winchester.com/lawenforce...spx?storyid=11
straight from the site;
223 Rem VS 5.56mm

* The cartridge casings for both calibers have basically the same length and exterior dimensions.
* The 5.56 round, loaded to Military Specification, typically has higher velocity and chamber pressure than the .223 Rem.
* The 5.56 cartridge case may have thicker walls, and a thicker head, for extra strength. This better contains the higher chamber pressure. However, a thicker case reduces powder capacity, which is of concern to the reloader.
* The 5.56mm and .223 Rem chambers are nearly identical. The difference is in the "Leade". Leade is defined as the portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. It is also more commonly known as the throat. Leade in a .223 Rem chamber is usually .085". In a 5.56mm chamber the leade is typically .162", or almost twice as much as in the 223 Rem chamber.
* You can fire .223 Rem cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity over firing the .223 round in the chamber with the shorter leade it was designed for.
* Problems may occur when firing the higher-pressure 5.56mm cartridge in a .223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads and gun functioning issues.
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* The 5.56mm military cartridge fired in a .223 Rem chamber is considered by SAAMI (Small Arm and Ammunition Manufacturers Institute) to be an unsafe ammunition combination.
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[Legion_Prime]

I'm not sure I understand why Colt would ever have any desire to cut a .223 chamber into one of their barrels.