Pillar/skim bedding question

Discussion in 'Gunsmithing' started by WapitiBob, Jan 31, 2012.

  1. WapitiBob

    WapitiBob Well-Known Member

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    I have seen two schools of thought on pillar bedding techniques. One, the action and the btm metal only touch the pillars, with a non load bearing bed around the action.

    The other, the action is on the pillars with the non load bearing bed around it, and the btm metal is up tight into the stock.

    Is there any significant difference, accuracy potential wise?
    Also, with an aluminum bed block style stock, it would seem that the btm metal would have to be tight up into the cut out.
    Do you really need to care about the btm metal?
     
  2. Greyfox

    Greyfox Well-Known Member

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    I prefer the pillars/or block extend to include contact with the bottom metal. In this case you can torque the stock screws to 65#. This eliminates the possibility of the stock compressing over time. If the bottom recess for the bottom metal/trigger guard assembly is mated to the synthetic stock material or wood should back off the torque to 40-45#. I also use non supporting bedding with pillars or just skim coat a bedding block. I also bed the first couple of inches of the barrel where it meets the recoil lug.
    As to whether all this effects accuracy, sometimes yes, sometimes no. But it's good practice and rules out poor accuracy due to bedding issues.
     

  3. J E Custom

    J E Custom Well-Known Member

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    The main reason that we pillar bed is to prevent the action from moving or changing the fit
    of the stock to the action under all conditions Firing, humidity,heat,cold,shooting positions
    and anything else that would make the rifle inconsistent.

    Accuracy is also affected if the fit is not absolutely stable.

    So it is not so much the method but the end results.

    Some shooters actually glue the action into the stock to make sure it doesent change.

    I believe in doing a full pillar and bed so that if it does not like it it can be removed in certain
    areas by small amounts until it does what you want.(This does not happen often but on several
    occasions I have "Tuned " the bedding) and the results were great.

    Like some stock materials a good bedding job helps manage the harmonics.

    J E CUSTOM
     
  4. sp6x6

    sp6x6 Well-Known Member

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    I dont really understand your question? Bottom metal up tight in stock? It should be in same basic relationship it started ,for fit and finish. For optimium the pillars go from metal to metal. Probably a video here some where. I live close to the,old Lonewolf Stocks and did trade w/ Bob, so I have some insite. If you get Score High pillar kit, they send a nice dvd on process and tips.They use nice adjustable alum. pillars, different types for diff. actions. In their vid. you drill complete through stock for pillar. Pillar is threaded and has inside adjustable sleeve for setting proper height. You can use custom pilot bit, or plug hole and redrill. or get fancy like the smiths that do it for a living and have jig and mill.The kit is handy with reusable handles that hold trigger guard and assembly together. I dont know if this is best way and I have used old bolts and spring clamps w /out guard and no risk of mess on it and had good results. If I had some type of Kevlar glass stock then I would think it ok to go to the Shell so to speak w/pillar as I WOULD NOT SEE that compressing and leaving a clean job
     
  5. WapitiBob

    WapitiBob Well-Known Member

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    To rephrase the question, I have seen the pillars extended above and below the stock mtl so both, the barrel and the btm metal touch only the pillars. I have also seen where only the top of the pillar is extended, which results in the btm metal being tightened up against the stock cut out.
    If the stock is synthetic, does it matter which method is used?
     
  6. sp6x6

    sp6x6 Well-Known Member

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    Ok, I would say no, this is comparing to my kevlar glass type stocks, such as my Lonewolf. The pillar goes to the inside of the Shell of the stock at the bottom.
     
  7. Bart B

    Bart B Well-Known Member

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    Wel, all the epoxy bedding materials I know of expand when hot and contract when cold. Which means it doesn't make any difference if there's a round metal bushing around the stock screws and epoxy of some thickness around the rest of the receiver or no pillars at all. When it's cold, the only hard, bedding points are at the pillars; they don't shrink as much as epoxy. The rest of the receiver's not held as tight on its bottom nor any place else. With conventional epoxy bedding, there's more receiver bottom to bedding contact when it's cold; expecially around the stock screws.

    Having shot the same two or three rifles in all sorts of temperatures and humidities from the 20's up to almost 100, they all held the same accuracy level with the same load. No pillar bedding. Just plain old full contact epoxy except for the bottom of the recoil lug which is clear of any epoxy.

    Of course one should retorque their stock screws before each shooting situation. ths assures the same compression force at the stock screw areas regardless of the type of bedding.

    The most accurate shoulder fired rifles I know of are all conventionally epoxy bedded. No pillars at all.

    And don't forget; the receiver expands when hot and contracts when cold; just like pillars.
     
  8. J E Custom

    J E Custom Well-Known Member

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    All different materials have a different coefficient of expansion. but in a properly bedded action
    the bedding thickness is minimal and has little or no effect on expansion or contraction.

    Most bedding materials are low shrink materials in order to maintain contact with the action
    at all times

    The main reason for pillars in the bedding system is to keep the action screws from crushing
    the stock material to the point of yield and lowering the torque on the action screws.

    All stock materials can become compressed over time with the exception of the machined
    aluminum stocks. Pillars will expand and contract based on the material used but with
    recomended torque loads they will not compress and remain in that condition.

    If good pillars and metal to metal to metal contact is achieved re-torquing is rare unless you
    remove the action from the stock.

    J E CUSTOM
     
  9. ken snyder

    ken snyder Well-Known Member

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    With the exception of the angled bottom screw like the M77, the pillars have nothing to do with recoil because that is the recoil lugs job. A pillars only job is to keep the stock from compressing when the bottom screws are tightened.

    Soft Material stocks such as wood or the soft non reinforced tupperware brands need them. Hard Stocks like fiberglass, carbon fiber do not need them and can be used the way they are shipped.

    Soft material stocks do not skim because the bedding cracks out and they need to have different areas enlarged so the bedding is thick enough not to crack. The hard reinforced fiber stocks all use a resin to hold those fibers together which for all practical purposes if compatible is exactly the same thing that our bedding material is ( they are all Polymers) and if temperature makes a difference to a relatively thin bedding just imagine how much difference is being made to the entire stock I'm pretty sure everyone has a different thought on how to bed and pillar and I cant really say that the differences make any difference at all as long as they have been nicely done and with the right thoughts in place
     
  10. Bart B

    Bart B Well-Known Member

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    Regarding the stock material around the stock screws, one company used a good method to keep virtually the same exact bedding pressure between receiver and its bare wood stock. Anschutz put wave washers between their smallbore match rifle stock screw heads and the stock. This spring loaded the pressure between receiver and stock. Temperature and humidity changes would cause their wood stocks to swell and shrink, but the bedding pressure remained virtually the same.