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Thread: Vltor gas block/front sight assy torque test

  1. #1
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    Vltor gas block/front sight assy torque test

    the subject of the clamp-style gas block/sight assemblies and how susceptible they are to movement due to constant pressure from a sling or impact has been brought up before.
    it's a no brainer that a taper-pinned gas block is the most secure and damage to other parts of the rifle, including the front sight will occur first before the gas block moves on a barrel.
    i talked to the guys at vltor, and asked if they'd be willing to perform a test to see how much it actually takes to move a properly installed clamp-on gas block, like their VST-C1 or a PRI. they were interested in the results as well, and happily agreed. an impact test would have been too complicated to set up and quantify with so many variables, so we decided to go with a simple torque test. username and password are both 'mm' to view larger photos.
    http://www.militarymorons.com/weapon...s2.html#torque

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    That seems very conclusive. I have often wondered how the PRI units would handle a similar test. Thanks for sharing this!
    "We need to get over the romance of aligning sights and get to the business of shooting smelly bearded men in the face more efficiently."
    Pat Rogers

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    Yes, thanks for setting that up and sharing.

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    Quote Originally Posted by Pinnacle View Post
    That seems very conclusive. I have often wondered how the PRI units would handle a similar test. Thanks for sharing this!
    I was concerned about how secure the PRI flip-up front sight/gas block would be with the clamp-on bolts, so I asked my gunsmith; he pointed out that similar bolt-ups are used on the forks of motocross motorcycles. That was proof enough for me.

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    Good stuff and should put peoples minds at ease.



    C4

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    MM,

    Thanks very much for sharing this. Very informative.

    Stephen

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    Interesting...

    I am more curious about frontal impacts howevever -- since I have seen two PRI's come out of alignment from that.
    Kevin S. Boland
    Manager, Federal Sales
    FN America, LLC
    Office: 703.288.3500 x181 | Mobile: 407-451-4544 | Fax: 703.288.4505
    www.fnhusa.com

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    hey kev, i agree - i'd be more concerned with an impact than a constant torque or pressure, but that's a tougher test to set up.
    i can understand your concern, based on your personal experience with the PRIs - do you have an idea if their movements were caused by impact or related to incorrect (over or under) torque, or the bolts loosening up after time, or some other factor?
    here are a couple of points about the vltor that differs from the PRI:
    - the PRI flip-up sight locks in the 'up' position. if hit from the front, the shock is transferred through the locking mechanism to the gas block. the vltor sight does not lock up - it's detent loaded. an impact from the front or at an angle to the sight itself will fold it. as for side and rear impacts to the sight, the sight will bend before the gas block moves. some people like that, some don't, but that's why it was designed that way - to minimize the possibility of gas block movement from an impact to the sight.

    - the vltor gas block has two divots beside the clamp bolts. the ends of the bolts are center punched (bolt metal is moved into the divots) which stakes the bolts, in addition to using blue loctite after the gas block is torqued. the staking prevents the bolts from backing out and loosening up from normal use, and losing torque.

    vltor is not claiming that the clamp-on gas block is as secure as a pinned one - but they've tried to ensure that their gas block is as secure as the clamp design allows, and that might be enough under most circumstances (for a civvie like me who doesn't want to send the barrel out for pinning). time and usage in the field will tell.

    but if for people like you whose lives depend on your weapons, and the additional peace of mind of a pinned gas block is desired, then their pinned-on version should address that.

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    Quote Originally Posted by militarymoron View Post
    for a civvie like me who doesn't want to send the barrel out for pinning...


    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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    Cool testing. Personally I would never trust a non pinned block with my life if given the choice.

    Pinned blocks cannot move laterally or fore or aft (unless both pins are sheared, if that happens you're probably already SOL). This is why for custom builds that I build I just 'shave' the FSBs into low profile gas blocks and refinish to fit under LaRue rails and DD Lite Rails. If a customer brings me a barrel that didn't have a FSB I use a VLTOR gas block and dimple one of the set screws and make sure the rail or FF tube covers the gas block.






    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

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