Accuracy in LW Barrels

[ra2bach]

In general, does anyone who is using a LW barrel have an accuracy issue relating to the profile of the barrel?

How about after it heats up - are your shots stringing?

[Molon]

I conducted an accuracy evaluation of a 16” Colt light-weight barrel from a distance of 100 yards with the results shown below. The Colt light-weight barrel has a barrel diameter of 0.625” at the gas block and approximately 0.57” forward of the gas block. The barrel profile has a slight taper underneath the handguards from the chamber to the gas block with an average diameter of approximately 0.64”. The stripped light-weight barrel weighs approximately 1 pound, 6 ounces.

The light-weight barrel is chrome lined, has a NATO chamber and a 1:7” twist. This barrel employs a carbine gas system and has M4 feedramps. This is the barrel traditionally found on the Colt model 6520 and now the Colt model 6720. This accuracy evaluation was performed with a LaRue Tactical free-float handguard installed.

Colt 6520

http://www.box.net/shared/static/6nr4ltc77g.jpg



Colt 6520 converted to a flat-top with a Colt M4 upper receiver

http://www.box.net/shared/static/lrvo5hc034.jpg



Carbine gas system

http://www.box.net/shared/static/da2px7xty3.jpg



The barrel stamp.

http://www.box.net/shared/static/5ocnqzzcmh.jpg



M4 feed ramps

http://www.box.net/shared/static/xvmv9mriy1.jpg




The stripped light-weight barrel weighs approximately 1 pound, 6 ounces.

http://www.box.net/shared/static/2946jlgf3n.jpg




The test vehicle.

http://www.box.net/shared/static/b3lq26fcpa.jpg


Shooting was conducted from a concrete bench-rest using a Sinclair Windage Bench Rest in front and a Protektor bunny-ear bag under the stock. The ammunition used; match-grade hand-loads topped with Sierra 55 grain BlitzKings. Sighting was performed using a Leupold VAR-X III with a mirage shade. Magnification was set at 25X and the scope was adjusted to be parallax free at 100 yards. Wind conditions were monitored using a Wind probe.

Six 10-shot groups were fired in a row in a slow and steady manner. Those groups had extreme spreads of:

1.18”
1.92”
1.28”
2.53”
0.96”
2.24”

for an average extreme spread of 1.69”. Using RSI Shooting Lab, I over-layed all six groups on each other to form a 60-shot composite group. The composite group had a mean radius of 0.56”.


http://www.box.net/shared/static/z63cvxm04g.jpg



The smallest 10-shot group.

http://www.box.net/shared/static/pny6ravij6.jpg



The largest 10-shot group.

http://www.box.net/shared/static/mikliee7f7.jpg




http://www.box.net/shared/static/08zo1sz3bu.jpg

[ALCOAR]

That is my favorite evaluation you've done...love the 6520 barrel.

http://i51.tinypic.com/2eyjec7.jpg

[g5m]

Nice post, Molon.

[500grains]

Excellent thread. I wonder how the Daniel Defense and BCM barrels do on the same test. Also, I wonder how 77 gr Match kings would change the Colt's groups.

[Molon]

Also, I wonder how 77 gr Match kings would change the Colt's groups.



They would have been larger. The barrel showed a preference for the 55 grain BlitzKings.


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