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Thread: High failure rate of PMR bolts

  1. #1

    High failure rate of PMR bolts

    So I got a broken PMR for free from my local field owner that had a snapped bolt that I just replaced. This seems like a relatively common issue from what I've seen on forums. This kind of failure is also seen with bolts of similar design, like Ions and DMs, but it doesn't seem as prevalent. The PMR bolt differs in that it undergoes cyclic loading in both tension and compression throughout a bolt cycle while Ion and DM bolts experience just tension. Could this be a factor in the high failure rates? If so, I can remove the larger two tail orings to prevent the compression loading, but it'll increase bolt speed, which might induce failure in the same fashion as Ion bolts from just banging back and forth.

    For reference:




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    Last edited by tyronejk; 12-13-2016 at 03:59 PM.

  2. #2
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    Not sure this is news, but I think in their haste for flow dye neglected the mechanical aspects of the ribs. Those connection points are tiny. I'd suggest going with higher tensile aluminum and adding more meat to the join.

  3. #3
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    Just looks like a bad design.
    Dear boy, I work at Planet Eclipse, don't you know..

  4. #4
    Insider AndrewTheWookie's Avatar
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    I never understood the reasoning for that extra tail section.
    I don't know, fly casual

  5. #5
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    They wanted more open speed at the end of the stroke instead of closing speed. Pretty dumb IMO, but they were also probably trying to separate their kit from the ion.

  6. #6
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    I figured they built it without and had trash bolt bounce costing them fps so they just decided to "boost" the end of stroke.

    Because band aiding bad designs is cheaper than going back to the drawing board again and again and again...

  7. #7
    trixes have always had pretty brutal bolt bounce. on the one side, i think that is actually one of hte reasons they feel so smooth.

    https://www.youtube.com/watch?v=GkB81aGU1M0

    the ion, which is the closest thin to a PMR, also doesn't have bolt bounce. the longer i go as an engineer, god, the more i respect the ion. it is by far the best gun SP ever made.
    Last edited by cockerpunk; 12-15-2016 at 04:59 PM.
    social conservatism: the mortal fear that someone, somewhere, might be having fun.

  8. #8
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    I have never seen a matrix do that. Looks to me like overdwell.

  9. #9
    Quote Originally Posted by ironyusa View Post
    I have never seen a matrix do that. Looks to me like overdwell.
    Typically that happens too fast for a human eye to catch it. I've seen it with many bolt designs over the years, it's never a good thing.

  10. #10
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    I have seen the m2 over high speed and haven't noticed anything like that. There was some small oscillation when I was working through the NT fix, but I got that sorted and the gun will shoot paint that breaks from just above knee high now.

    My assumption is that it's overdwell and the breach pressure is pushing the bolt back a tad before it decays to a point where the sail is still the driving force. Dropping dwell and raising LPR should stop the oscillation, right? Or is there some other explanation as to what's going on?

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