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Thread: High failure rate of PMR bolts

  1. #11
    Insider PBSteve's Avatar
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    It's not overdwell, that sort of thing happens immediately as the valve opens, it's mostly a geometry issue.

  2. #12
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    Geometry of what? It looks to me like it's bouncing at the end of the stroke. The valve has been open a while at that point.

  3. #13
    more forward bias would solve the problem too, abit making the gun kick more. that bolt slopping around in there is the reason why they feel so kinda mushy when you shoot them, not sharp at all, which folks call "smooth"

    i obviously have not filmed a matrix in some time, but all the old fuse bolt guns did it. even the pre-fuse bolt guns did it, as early as deep blue and tom tracking chamber pressure, you could see the bolt boucing around in the matrix.

    also, i think most matrix based guns, without some kind of secondary dump chamber sealing system, the "ideal" dwell is always WAY oversdwelled. bolt stays forward on them for so long ...
    Last edited by cockerpunk; 12-15-2016 at 11:38 PM.
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  4. #14
    Insider PBSteve's Avatar
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    Quote Originally Posted by ironyusa View Post
    Geometry of what? It looks to me like it's bouncing at the end of the stroke. The valve has been open a while at that point.
    Tail.

  5. #15
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    Could be caused by any number of things. Not enough exhaust on the forward stroke and/or poor LPR performance and flow on the forward stroke combined with not enough main valve overlap would be my guess. But what do I know..

    it would certainly contribute to the mushy quiet shot you got from those earlier Matix. Like shooting a Sniper or other pump gun and not holding the pump forward.
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  6. #16
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    The numbers game with matrices has always been kind of deceiving. For dye to drop the LPR pressure, they just increase the sail area. I'm pretty sure the newer versions also have about the same amount of biasing, but I'll have to see some high speed on the m2 to know for a fact.

    I also should differentiate that when I said overdwelled, I was speaking in terms of the solenoid and not the valve. I tend to think Jack is right and something is going on with the flow at the sail whether it be the LPR or solenoid. I'd be surprised if that oscillation helped velocity at all (from a valve dwell perspective), so it's useless actuation time at the sail.

  7. #17
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    It must create a horribly pinched valve dynamic. No wonder they always struggle with efficiency.
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  8. #18
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    That, and you know, 10 cubic meters of expansion volume.

  9. #19
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    lol
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  10. #20
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    My guess is that it's because of the way their geometry is laid out, the breech pulse acts on the bolt significantly. Couple this with a ton of static friction (they add something like 5 thou crush to the main seal at rest) and it amounts to effectively decaying force during the stroke. Bad lpr or solenoid flow would make this a lot worse. Plus you have an air spring that basically works exponential in throw, but the flow of the orifice is only linear in pressure. I'm not sure if the air springing is coming from residual front volume or blow back.

    There's a similar phenomenon in both the gamma core and paragon with the return of the bolt. Sizing of orifices becomes very important to balance bolt speed (orifice plate/ restrictor) and oscillatory behavior. Having a 2 or 3 stage system as both of these guns do allows you to skew way to the side of fast final bolt speed.

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