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Thread: tighten the carry handle on the m4

  1. #31
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    Y'all must have some weak hands, I've never had a thumbscrew work loose on my rifle and I've only ever made them finger tight.

  2. #32
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    hand-tight with a little blue loctite for good measure

  3. #33
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    Of course, after posting this answer to another thread, my Google Fu found this thread that I wanted in the first place:



    There is an ongoing debate as to how much to tighten the thumb nuts on a carry handle:

    1. Thumb tight (that's why they're called "thumb nuts")
    2. 1/4 turn or thereabouts past thumb tight with a quarter
    3. Tightened down as far as the thumb nuts will go with a quarter and a pair of pliers. "Spend the quarter" is the motto here as you will probably bend the coin out of shape using this method.

    The $64,000 question is whether overtightening is necessary to keep the sight from loosening, and whether excessive overtightening damages the carry handle or receiver.

    The answer to all questions is "yes".

    This is anecdotal evidence, but it has happened to two rifles (one Colt once BCM) and two quality carry handles.

    One carry handle had been torqued 1/4 turn past thumb tight with a quarter. One had been tightened until it wouldn't move any further with a quarter clamped in a pair of pliers.

    Here is the damage observed:

    1. Both AR upper receivers sustained a minor "mark" in the form of a disturbance to the finish, and a tiny, almost imperceptible indent where the carry handle had clamped the receiver. The indent was roughly the width of a line on a piece of paper and had a depth that was only noticeable under a bright LED light at certain angles under a magnifying glass. This appears to be mostly cosmetic since it happened to a solid part of the rail. It did not get any worse with removal of the carry handle for installation of other optics. The other optics both had quick-detach clamps. The indent would not have even been noticeable in normal use, i.e. unless a person were looking for it under an extremely bright light, it was barely visible.

    2. Both carry handles, on the other hand, sustained damage to the little "gasket" that goes up inside the thumb nut. Overtightening the thumb nuts harms this gasket. When the carry handle that has been overtightened is removed and then replaced, these "gaskets" on both carry handles shredded into strips as the thumb nuts were tightened a second time. This damage to the "gaskets" inside the thumb nuts did not prevent the thumb nuts from tightening down adequately, but in all cases the nuts were tightened past witness marks placed on them during the first tightening for reference.

    The BCM rifle with the overtightened thumb nuts had fired between 6,000 and 7,000 rounds after the carry handle was installed, with no loosening of the carry handle or any additional scoring or other damage to the receiver rail. I always put a drop of nail polish or black paint on the top of the thumb nut bolts (thumb nut side) to prevent loosening from vibration.

    Other rifles in which the thumb nuts were only hand tight suffered from loosening of the thumb nuts after less than 500 rounds (I did not take an exact round count; it could have been as few as 100-200 rounds before I noticed the loosening).

    Conclusion: overtightening does appear to damage both the receiver rail and the thumb nuts, but in the case of the receiver rail it appears to be largely cosmetic. The damage to the thumb nuts probably necessitates overtightening that carry handle from then on since the inner "gasket" sustains quite a bit of damage from overtightening.

    My take: I plan to use a large flat blade screwdriver or quarter to overtighten "just beyond" hand tight. A person with substantial hand strength may be able to get by with truly "hand tight". I have never had thumb nuts on an optic that did not eventually loosen when left just "hand tight", so if you plan to go that route then re-tightening the thumb nuts occasionally becomes part of the necessary equipment check.

    Personally, I have decided if I need a rifle with strictly iron sights, I will seek out an AR with a fixed carry handle and avoid the hassle altogether.

  4. #34
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    Please tell me

    Please help me.����



    I install my carry handle and use screwdriver to tighten the mount. But the carry handle moves rearward when I charge and close the bolt. It's fine or not . Thank you

  5. #35
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    I chopped my carry handle so I can use it behind my aimpoint. So it only has one thumb screw. I feel the thumb screw for tightnes every once in a while when I pick the rifle up. It's never been loose and if it was I would just tighten it up real quick. Not a problem.

  6. #36
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    The guys I shooting with switch between irons and optics regularly, with both mounts using thumbscrews. They always do 40 inch pounds and it always gets them a good return to zero. I don't know if it's too much but it's been working fine for us.

  7. #37
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    Consistency would be the key I think, whether it's thumbtight or if you measure it with a torque wrench.

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