Colt 6520 in 223 ???

[CJGarza]

Well I have decided to take the plunge and simply get a nice Colt carbine. It isn't the "kool aid" drinker in me, I just figure I want somthing that will work wneh and if I ever need it. I'd rather pay alot once and not have to put into the rifle time after time after time to get it to run properly. Seeing as I'm not really an optics kind of guy, the A2 platform works fr me (besides I can always swap the upper for an A3 later if I change my mind).

Anywho I found a nice used but very clean Colt AR15A2 carbine (LEO marked). It was $1300 but I know the guy and he'll let me get it for $1150. I took the rifle apart and examined it, it has all the marked parts (barrel, upper and lower) and that's when I noticed it is marked .223 and NOT 5.56!!! Now I know there is a difference between the two and that it is possible to safely shoot .223 through a 5.56 but not necesarily he other way around. Was it marked this way for export? Is it actually made for .223 and not 5.56?? I really need a Colt guru to point me the way on this one.

Another question is this: is there any real benefit to the M4 profile barrel over the lightweight barrel?


BTW they also had a nice Colt SP1 for $950 which I promptly put on layaway (weather or not I get the 6520 was moot, the SP1 was very nice).

[Ridgerunner665]

All of the Colt AR 15a2's (6520's) that I've seen are marked 223 (I haven't seen them all)... I honestly don't know the chamber dimensions...but I'd bet its 5.56.

I had an HBAR a2 back about 1989 that was marked 223 too.

[SethB]

Something is odd there... But lightweight is the way to go. I'd get a lightweight upper to go with it. An old Colt M16 upper would be nice.

[Robb Jensen]

Colt 6520s, 6721s, 6920s and some others are marked .223 on the lower receiver. The barrel is where it matters as it's marked 5.56 NATO and is chambered in 5.56mm NATO.

[OldNavyGuy]

i have been around AR-15 rifles since the beginning, and will never understand why some mfgrs. stamp the lowers ".223Rem." and have a "5.56mm NATO" barrel, it is a bit confusing, but every AR style rifle/carbine made today is a "5.56mm NATO" chamber.

[ST911]

6520 is a excellent choice in a basic carbine.

Others covered the chamber. Markings have been like that on all mine, from early 90s through most recent.

http://i76.photobucket.com/albums/j18/Skintop911/Diemaco%206520s/IMG_1678.jpg

http://i76.photobucket.com/albums/j18/Skintop911/Diemaco%206520s/IMG_1681.jpg

[SethB]

My 6920 is marked 5.56MM on the lower.

[Iraqgunz]

Since I am just a novice let me ask this question. What is the exact difference between the .223 and the 5.56? Are the specs so different that it will really cause an issue? When and how do these issues occur?

I am really curious because I have never seen ammo in .223 or 5.56 that says "Caution may not reliably function in a .223 or 5.56 barrelled weapon or vice versa.

[Eric]

The .223 roll mark on the lower is normal. The chamber is 5.56. The .223/5.56 issue has been beat up previously, but the Reader's Digest version... Your Colt will eat both. The 5.56 typically operates at a higher pressure and the chamber dimensions on the 5.56 are a bit more generous. Many .223 chambered weapons will choke on 5.56 ammo.
http://img.photobucket.com/albums/v503/AR15forme/Colt%20AR15/P1000723.jpg

[Ridgerunner665]

Since I am just a novice let me ask this question. What is the exact difference between the .223 and the 5.56? Are the specs so different that it will really cause an issue? When and how do these issues occur?

I am really curious because I have never seen ammo in .223 or 5.56 that says "Caution may not reliably function in a .223 or 5.56 barrelled weapon or vice versa.

Full power 5.56 NATO ammo is loaded to the same specs (pressures) as SAAMI PROOF LOADS for 223 Rem.


And on the SAAMI website...under "Unsafe weapons and ammo combinations"...it says not to use 5.56 ammo in a 223 Rem...I've never seen it printed on a box of ammo either, but I did do the research to find the difference because inquiring minds want to know.

SAAMI 223 Rem. pressure measured at the case mouth = 52,000 psi
NATO 5.56 pressure measured with a midcase transducer = 60,000 psi maximum...55,000 psi average

The midcase transducer gives lower readings than the case mouth transducer because it actually measures AFTER the pressure peaks. So peak 5.56x45 NATO pressure is upwards of 60,000 psi.

[rob_s]

My primary carbine started life as a 6520 and I've fired thousands of 5.56 though the 5.56 marked barrel without issue.

Doesn't look much like a 6520 now though.
http://i134.photobucket.com/albums/q111/rob_s/gun%20stuff/6520-01.jpg

[Robb Jensen]

My 6920 is marked 5.56MM on the lower.

Yeah you're right I think most 6920s are marked 5.56mm on the lowers.

[variablebinary]

My 6920 is marked 5.56

My 6520 is marked .223

[Robb Jensen]

This is from Randalls web site www.ar15barrels.com

http://img.photobucket.com/albums/v408/gotm4/0f79b90c.jpg



My 6721 Colt is marked .223 on the lower.

http://img.photobucket.com/albums/v408/gotm4/gunpics/56da8be4.jpg