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Prototype Portable Combination Pistol and Carbine (PCC) Machine Rest Build

Discussion in 'Handloading and Reloading' started by bds, Jun 1, 2019.

  1. RMH
    • Contributing Member

    RMH Contributing Member

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    For recoil management you might look into gas shocks. You can get them in a variety of mount configurations, length of stroke, and pounds of compression.
     
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  2. lordpaxman

    lordpaxman Member

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    I needed a large mass at one time for a different project and after trying to figure out how to manage 500 pounds, I decided to use the 2" receiver hitch of my truck. And you'll have the added advantage of detracting tailgaters.
     
  3. jmorris

    jmorris Member

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    I think it’s not only the impulse even static loads. If you can’t touch the bench without changing the POA, it likely won’t take the “hammer” of a shot. The slicker you make free recoil the better off you are in the latter case, less energy transfer from one to another.

    One interesting note in variation between Bart’s linked photos and most “unlimited” benchrest rifles are the angled front runners. That said IIRC it was made 60 years or so ago, may be a better way to skin the cat today but you always learn something from the past.

    50ADE6DA-DB68-4D56-8F5F-7407DCB7E99D.jpeg

    Makes the recoil run the muzzle up, just like a bag would let the stock down (muzzle up) with a regular rifle stock. If you needed more food for thought. Also note the attachment points of the rifle above, not just “sitting” in the mount.

    Unlimited br rifles these days are very linear and very “free”.

     
    Last edited: Jun 3, 2019
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  4. jmorris

    jmorris Member

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    I don’t think you have to have “hard mount” to have consistent repeatability. The machines that make the guns and optics we use on them, transverse some amount of distance. The rifles can too and be fairly repeatable.

     
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  5. Bfh_auto

    Bfh_auto Member

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    Cut plywood as close to size as possible and use fiberglass body filler to fill the void, remove the pistol, shave it just enough to get clamping force when bolting it in place. Leave room for bolts behind the pistol and below the trigger guard.
    Use a lot of release agent.
    This is all I can think of since my shock idea was already put out there.
     
  6. jmorris

    jmorris Member

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    On the subject of repeatability, I was curious about quantitative values and they could differ depending on how things are set up but here is one example.

    If we took a rifle that was 48” from the butt plate to the barrel, using a target that is 100 yards away .001” of movement (of only one end) moves impact point .075”. .003” of one end would be .225” and .013” would be almost an inch.

    The longer you make the fixture, assuming the rifle does not move in it, the better things get, the closer together contact points get (shorter fixture) the more precise they need to be to be able to achieve the same accuracy.
     
    Last edited: Jun 6, 2019
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  7. bds

    bds Member

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    Yes, I have studied the difference in designs and how they "evolved" to handle recoil vs return zero.

    That's very good point. I was thinking of using friction between bottom of platform and top of table to manage recoil force but may need to rethink that.

    I am still thinking hard mounting barrel in the way of attaching free-float/handguard is better over "nesting" carbine/rifle in a cradle as there are many points of play that could "stack".

    That's where I was going with the prototype machine rest build.


    The video obviously gave me something to chew on but I need to build a "universal" machine rest. The rifle in the video is purpose built and I doubt I can repeat what's shown in the video with an average quad rail/free-float AR.

    I do like the free-recoil design which would jar the firearm and bench less.

    A LOT to think about. :D
     
  8. bds

    bds Member

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    Something more for me to chew on. You are expanding "working" regions of my brain. ;) (Wife and daughter are increasingly claiming I have many "dead" regions of brain :confused:)
     
    Last edited: Jun 6, 2019
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  9. jmorris

    jmorris Member

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  10. bds

    bds Member

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    Nice!

    More to think about.:thumbup::thumbup::thumbup:
     
  11. Demi-human

    Demi-human Member

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    So the "ramping" of the recoil movement. Would this upward movement be more consistant to shot placements as opposed to straight rearward?

    I imagine the levering keeps the harmonics of the barrel perpendicular to gravity. Keeping faster shots higher, rather than just further from group center.

    Does this sound correct?
     
  12. bds

    bds Member

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    Update to jmorris' points:

    I thought things over during lunch and while mowing our acreage with turkey chicks following me (I thought they imprinted on my wife but they act like I am their momma too :().

    I thought about abandoning my low friction platform/table idea and going with roller/rod with spring "free recoil" I originally was thinking of. BUT I think I am going to try the low friction platform/table idea first and if the resulting consistency/repeatability is measurably poor, then I would have something to reference when I use the roller/rod with spring "free recoil" set up. ;)

    I could also consider using bearings out of fidget spinners as "low friction" bearings (They are like $2 and have 4 bearings) unless I could buy bulk bearings cheap. Kinda like these - https://www.onlinebearingstore.com/10lot-608-zz-8x22x7mm-skating-ball-bearing.html

    I am thinking baby steps ... and trying to keep it simple. As to plywood copies, I am thinking roller drawer slides unless I find something simpler/cheaper.

    Thoughts?
     
    Last edited: Jun 6, 2019
  13. jmorris

    jmorris Member

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    Not sure how you plan to implement the roller bearings exactly.

    One can embed a bearing into just about anything. I used 4 embedded into the aluminum of one of my runout gauges.

    64EE9305-6EB4-4D2A-BF41-DF6C1E5D4C43.jpeg

    Gives you a hardened surface to work off of, something with a “V” that rides on top of or the ball sits into will be as linear as the V is. The other option is as above use a precision round and have the V portion ride on the round.

    Either would work when weight is sufficient to maintain contact with both parts. If that doesn’t exist then the guide would have to be very precision or the “slop” would allow it to move so much, it would become useless for the job.

    Kind of like a drawer slide can be pretty smooth but lift up on the handle and it comes up too, even if your not lifting the cabinet it’s mounted in.

    There are similar concepts that are precision though and others that are suitable as well.

    https://www.pbclinear.com/

    You might even be able to construct a prototype using product samples from companies like the above.

    I did this one using a linear guide, it’s precision and restricts any non linear movement to a high degree of precision despite not being super heavy.

    32E4907D-F42D-4E68-839E-93B62958E06B.jpeg
     
    Last edited: Jun 6, 2019
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  14. Demi-human

    Demi-human Member

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    I just viewed the videos.(Utoob hates me, but I convinced her...)

    Those rail guns are awesome! They look as though they are spring returned.
    And the rested rifle looks like it is on the same frictionless bearings, even though it isn't. That is truly neat.:thumbup:

    The hardest part will be getting it to work with pistols and rifles. The rifles being easiest, I think.

    But these unlimited rifles all were linear in their recoil. Unless there was something I could not see. I am flummoxed by the angles on the older rig. If not for simulated stock drop, are they to slow the rifle? Is this a Red Herring? I am only a carpenter, I could use a hint.:)
    Speaking of which, I'd better get to the hospital. Those new Auto-Claves aren't going to install themselves into a custom built wall unit sealed for washdown.
    Ugh. Night Work. In a Tyvek suit...
     
  15. bds

    bds Member

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    This is the bearing (From fidget spinners) I was talking about. I was planning to use them for "low friction" recoil set up and also to limit X/Y axis movement using adjustable or tensioned brackets.

    miniature-ball-bearing-fs-608-open-c3-tn-8x22x7-mm.jpg
     
  16. drband

    drband Member

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    I don't see how a machine rest will be useful unless it is anchored on an un-moveable mount/table. The tolerances required to replicate the aim point seem too small to allow a moveable set-up. However, I would like to be proven wrong! @bds, I hope you are successful!

    I know the current project is not for precision long range shooting, but the concepts are the same... see below...

    https://precisionrifleblog.com/2013...-warehouse-lessons-in-extreme-rifle-accuracy/
     
  17. <*(((><
    • Contributing Member

    <*(((>< Luke

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    You guys are smarter with more skills than I, but there are also linear magnetic dampeners, I like the fact that it is a finite, unchangeable force in relation to the object it is opposing. That may be something to look into. I'll just sit on the sidelines and eat my popcorn, while the adults talk.
     
    Last edited: Jun 7, 2019
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  18. lordpaxman

    lordpaxman Member

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    There are also linear bearings such as these:
    https://www.automationdirect.com/ad...MIkcKIzd3X4gIVgh-GCh3CNAwJEAAYASAAEgLH0vD_BwE

    To manage the recoil energy have you considered something like an ATV strut?
    https://www.gopowersports.com/shock-heavy-duty/?gclid=CI3XgZTf1-ICFYKNyAodbzsMNw
     
  19. bds

    bds Member

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    Now you understand why it took me so long to research prototyping a "portable" machine rest. ;) My poor brain ... what little neurons still firing ... doing their best ... :D

    We will find out on our initial test firing. You will get front row seat of groups prototype produces.

    Me too. If not, I am sure jmorris and THR peanut gallery will provide plenty of suggestions.

    If proof of concept can be repeated with pistols at 25 yards, I will be testing carbines at 50 yards and then rifles at longer distances.
     
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  20. bds

    bds Member

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    OMG, that's a great idea.

    See, why many brains are better than my burnt out lone brain. :thumbup::thumbup::thumbup:
     
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  21. bds

    bds Member

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    Yes, I did look at them but decided on fidget spinner bearings because I plan to use adjustable/tensioned brackets.

    ATV strut would be overkill. I would only need hatch strut/strong arms but even those would be too much.

    My guess is I need to tame only a few pounds of recoil force for pistol/PCC loads. I may look at more beefy recoil management when we approach rifle loads.
     
  22. Blue68f100

    Blue68f100 Member

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    A small adjustable oil dampener may work. Just a small piston reservoir and a adjustable valve (needle). It would give you fine tune options.
     
  23. bds

    bds Member

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    Adjustable recoil management system ... I like it! :thumbup:
     
  24. bds

    bds Member

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    Did some research reading on recoil and found this article on Ransom Rest testing and recoil movement measurement - https://www.ssusa.org/articles/2017/6/19/gunpowder-selection-for-controlling-recoil/

    With 124 gr bullet weight loaded to 1025 fps to 1100 fps, recoil movement measured on Ransom Rest was around 2.0 to 2.5 inches.

    I am already pushing 100 gr bullets to 1500 fps out of my carbines and was planning to push RMR 95 gr bullets even faster. May even test 9mm Major loads pushing 124 gr bullets to 1400-1450 fps using 40-9 conversion barrels with thicker chamber/barrel walls.

    For my prototype machine rest, I was planning to allow 3-4 inches of recoil travel on low friction platform. But with finished platform to weigh around 35-40 pounds (10/11 gauge stainless steel plates weight quite a bit), recoil movement from pistol may be less. I anticipate more recoil movement from carbine and rifle.

    For plywood/metal hardware copy machine rest with lighter weight, I am thinking of using balanced spring tensioned recoil management.
     
    Last edited: Jun 9, 2019
  25. fxvr5

    fxvr5 Member

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    The important feature for using 9 Major is having enough case support to prevent the case from rupturing. The chamber wall thickness on some 9mm pistols is sufficient. People are building 9 Major guns on 9mm Glocks and S&W M&Ps.
     
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