Colt AR-15 20” A2 Barrel Accuracy




This Colt 20” A2 barrel started its life on a factory-built Colt 6551. This was a pre-ban rifle, but this barrel did not have one of those evil, havoc-wreaking bayonet lugs.  It’s otherwise essentially the same barrel found on the Colt M16A2 and M16A4 as well as on “civilian” variants of those rifles. The barrel has a government profile, a chrome-lined NATO chamber and bore and a 1:7” twist.  The barrel stamp reads:

C MP 5.56 NATO 1/7

I installed the barrel on a Colt flat-top upper receiver and free-floated the barrel with a 12” Knight’s Armament free-float hand-guard. I conducted the accuracy evaluation from a distance of 100 yards from my bench-rest set-up using match-grade hand-loads topped with the Sierra 55 grain BlitzKing.











I conducted an accuracy (technically, precision) evaluation of the 20” Colt A2 barrel following my usual protocol. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group-reduction techniques (e.g. fliers, target movement, Butterfly Shots).
The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for.


All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III with the magnification at 25X and the scope adjusted to be parallax-free at 100 yards. A mirage shield was used. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.







The Wind Probe.





This barrel turned in a 3-shot group at 100 yards with an extreme spread of 0.180”.





This barrel produced a 5-shot group at 100 yards with an extreme spread of 0.516”.





Six 10-shot groups fired in a row from this barrel at a distance of 100 yards had an average 10-shot group extreme spread of 1.35”.

The smallest 10-shot group had an extreme spread of 1.085”.







A 30-shot composite group had a mean radius of 0.42".












Coming Soon:  Colt AR-15 20” A4 Barrel Accuracy


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Thank you for the great post. Looking forward to the A4 results.

Attached File


This is my Colt.  I am really looking forward to seeing your AR15A4 review.

I was like - Hey his looks like a Molon thread - Oh wait it is.

Always entertaining and illuminating!

Thank you.  Excellent as usual.  For a skinny, GI barrel it sure seems to shoot well.

ETA - Molon, just out of curiosity do you use the same lower for your accuracy evaluations?  Do you have a trigger that you prefer?

I'm rather partial to my SMOS billet lower receivers. I use a Geissele High Speed National Match trigger for accuracy/precision evaluations.








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Thank you.  Your test protocol demonstrates the value of multiple 10 shot groups.  The barrel did well.

More proof that quality bullets shoot very well even when fired from factory rack grade barrels.

1 moa +/- ten shot groups from chrome lined issue barrel should make anyone smile.

Yes.


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Excellent information and thank you for taking the time to showcase this. I greatly look forward to these types of tests.

Pretty impressive for rack grade!

A 30-shot composite group had a mean radius of 0.42".






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Molon Lives!

Yes. It is good.

If a barrel won't shoot the 52 grain SMK well, odds are the bullet isn't the problem.

Could, or would, consider testing the drop in accuracy of the same barrel with a kac m5 ras installed?

The data is in the can.  I just have to write everything up.

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