Accuracy Evaluation of a Colt 16” Light-weight Barrel
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
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Colt 6520 converted to a flat-top with a Colt M4 upper receiver
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Carbine gas system
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The barrel stamp.
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M4 feed ramps
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The stripped light-weight barrel weighs approximately 1 pound, 6 ounces.
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The test vehicle.
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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. Also, a control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.
All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. 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 set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.
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The Wind Probe.
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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”.
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The smallest 10-shot group.
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