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Thread: Bolt Lug Tolerance/Spec

  1. #21
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    Quote Originally Posted by bp7178 View Post
    The rule about contacting the company has nothing to do with disclosing their name. It's to keep someone from bad mouthing a shop without giving them the chance to rectify the problem.

    Again, I really doubt this is a lug dimension issue. They just don't fit that tightly. I really suspect this has more to do with how the bolt is timed, ie its not in its fully unlocked position when it should be.

    As for the bolt face idea, is this only when ammunition is present? Or does it do it when retracting on an empty chamber?
    Only when ammo is present. It may be a bolt-face depth dimension. I don't know. None of the other bolts I have do this in these guns.

  2. #22
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    I just measured a new BCM bolt that I bought about this time last year.

    Lug length=.278
    Lug width=.098
    Lug height=.110
    Face recess=.125

    All measurements +-.001

    If dimensions check out, is ejector binding in its hole and putting pressure on cartridge?
    Last edited by DBR; 07-16-13 at 14:26.

  3. #23
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    Do you have the means to measure a fired case? Datum line on the shoulder to base?

    You may have answered this already, but did you check it with any headspace gauges?

  4. #24
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    Quote Originally Posted by bp7178 View Post
    Do you have the means to measure a fired case? Datum line on the shoulder to base?

    You may have answered this already, but did you check it with any headspace gauges?
    I do not. I don't have the correct tools to fully measure the bolt, nor am I keen to fire the weapon with it for obvious reasons.

  5. #25
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    Quote Originally Posted by DBR View Post
    I just measured a new BCM bolt that I bought about this time last year.

    Lug length=.278
    Lug width=.098
    Lug height=.110
    Face recess=.125

    All measurements +-.001

    If dimensions check out, is ejector binding in its hole and putting pressure on cartridge?
    I did not detect any binding.

  6. #26
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    Quote Originally Posted by WS6 View Post
    I do not. I don't have the correct tools to fully measure the bolt, nor am I keen to fire the weapon with it for obvious reasons.
    If the round will chamber and lock up, you can fire it.

    But yeah... you'd still want an in spec bolt in the long run.
    "You people have too much time on your hands." - scottryan

  7. #27
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    Quote Originally Posted by markm View Post
    If the round will chamber and lock up, you can fire it.

    But yeah... you'd still want an in spec bolt in the long run.
    Well, I might give it a shot or two, then. I was just very leery of firing a bolt in my weapon which locks up differently from every other bolt, for obvious reasons. I am not 100% sure WHY it is locking up this way, and I didn't want a permanent reminder that headspace matters.

  8. #28
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    One other area to consider

    While having read through this post I do feel the BOLT is the issue from what has been shared. Consider that the bolt needs to rotate before it can smoothly clear the barrel extension. If the cam pin and it's relation to the carrier is delaying that rotation the bolt will feel sticky.

  9. #29
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    I had some stuck cases that took a light mortar to get out when I first started reloading and from my experience it doesn't take much deviation from headspace specs to end up with a stuck case. If good bolts are measuring 0.278 along the lugs and your problem bolt is 0.280, that 0.002 difference is plenty to cause problems. The min/max chamber dimensions only allow for 0.010 total variation anyway. Long lugs put the bolt face closer to the datum line in the chamber. Possibly combined with a bolt face that is too shallow and there isn't enough room to freely accept a cartridge. The cartridge is squeezed into the chamber by the cam action of the bolt and the extra friction on the bolt face makes it harder to rotate out of battery.
    Last edited by Eric D.; 07-16-13 at 19:27.
    B.A.S. Mechanical Engineering Technology

  10. #30
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    I just measured a new BCM bolt. Lugs were 0.103 x 0.278. Bolt face measured 0.125 deep.

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