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Thread: To pencil or not to pencil

  1. #41
    Join Date
    Nov 2008
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    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





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





    Carbine gas system





    The barrel stamp.





    M4 feed ramps






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






    The test vehicle.




    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.









    The 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”.







    The smallest 10-shot group.






















































    ….
    All that is necessary for trolls to flourish, is for good men to do nothing.

  2. #42
    Join Date
    Oct 2015
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    Vietnam was fought with pencil barrels.

  3. #43
    Join Date
    Mar 2008
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    Quote Originally Posted by Rotorhead84 View Post
    Vietnam was fought with pencil barrels.
    Yeah and they did a bit of rapid fire also.

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