Torque Recomendations

Discussion in 'Gunsmithing' started by J E Custom, Apr 11, 2008.

  1. J E Custom

    J E Custom Well-Known Member

    Messages:
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    The question has been asked on several occasions
    what the torque for bedding screws and scope bases
    should be so I though this might be helpfull.

    "NOTE" These are based on full engagement of threads.

    Wood, Fiberglass or Synthetic stock without bedding pillars-
    40 inch-lbs.

    Wood, Fiberglass or Synthetic stock with bedding pillars -
    up to 65 inch-lbs.

    Hard-use service-type rifles in synthetic with pillars-
    up to 65 inch-lbs.

    Law enforcement & military rifles are 65 inch-lbs on each
    of the guard screws.

    On rifles with three guard screws the middle screw should
    be only slightly tightened.

    Scope base screws 30 inch-lbs "MAX"

    Windage screws 30-40 inch-lbs "MAX"

    Scope ring screws (Aluminum Rings) 10-15 inch-lbs "MAX"

    Scope ring screws (Steel Rings) 15-20 inch-lbs "MAX"

    Note' If scope base and ring Screws have less than 5 threads
    of engagement they should be replaced with longer ones.

    Barrel to receiver Torque 35 ft/lbs minimum to 95 ft/lbs Max.

    If an anti seize compound is used instead of a light oil use 65
    ft/lbs max to prevent over torquing.

    I hope this will help
    J E CUSTOM
     
  2. scsims

    scsims Well-Known Member

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    Is there any way to guess in the bedding screw torque? I mean screw snug then 1/2 turn or something like that?
     

  3. J E Custom

    J E Custom Well-Known Member

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    Scott

    I allways change out the screws if they are not allen or torx
    head screws to get proper torque values on the screws.

    With ether the torx or allen wrenches ( L shaped) you can only
    apply about 20 to 30 inch/lbs to 1/4-28 bedding screws. and with
    6/40 to 8/32 screws about 15 to 20 inch/lbs with out bending
    the wrench.

    Inch/pound torque wrenches are a must if you take your rifle
    out of the stock for cleaning or other reasons,if you want it
    to return to or near the same zero.

    Brownells sells torque wrenches fairly cheep.

    J E CUSTOM
     
  4. BHP9

    BHP9 Well-Known Member

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    Good info Scott.

    Maybe this should be made a sticky.
     
  5. Moman

    Moman Well-Known Member

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    J E Custom, thanks for taking the time to post this, it's good info. Can you tell me what procedure for tightening the action screws you use. Which screw is torqued first? etc.
     
  6. J E Custom

    J E Custom Well-Known Member

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    I start by making up the action screws by hand ( Snug ) front
    screw first then the rear next.

    Then with the torque wrench I start the front at 20 inch/lbs and then
    the rear.

    If it is the first time fired after bedding I go up in 10 inch/lb increments to
    35 to 40 inch/lbs and let it set for several days before shooting.

    At the range I will fire a 5 shot group and let cool and clean, then raise
    the torque in five inch pound increments and shoot 5 more rounds and continue
    the procedure (Shoot,clean and torque) untill there is no improvement
    in the group size.

    This allows the bedding to be seated in properly, but no more than nessary.

    Once the optimum torque is reached the in/lbs goes in the load data for
    that rifle for future reference.

    On rifles that have heavy recoil I have had to work all the way up to 65 inch/lbs.

    "NOTE" This procedure will work on all stocks but dont exceed the max recomended
    torque for the type of stock and bedding system your using. Also I like to wait 4 or 5
    days after bedding to start this process even though the bedding manufacture may
    say 24 hours is enough time.

    This is the way I do it and even though it may seem like overkill it works well for me
    and is very consistent (repeatable) each time the barreled action is removed from
    the stock.

    Good Luck and I hope this helps.
    J E CUSTOM
     
  7. Aldon

    Aldon Well-Known Member

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    bump................
     
  8. happylilcuss

    happylilcuss Well-Known Member

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    Bringing this to the top just for reference for the new guys.
     
  9. shortgrass

    shortgrass Well-Known Member

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    more info;
     

    Attached Files:

  10. Fitch

    Fitch Well-Known Member

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    J. E.

    Excellent post on the torques.

    I tend to use 25 in-lbs max on #6 torax drive scope base screws. For me, the 30 in-lbs works better on torax drive #8 screws.

    In my experience, rifles with 3 action screws are almost always better off if the middle screw is either left out or screwed into something other than the receiver. I've been known to epoxy metal pieces in the stock for the screw to thread into if it has to hold something like the front of the trigger guard.

    It's just about impossible to install the third screw so it won't stress the receiver (2 points make a line, 3 points make two line segments that are perfectly aligned only by coincidence). My LRPV has about as stiff a receiver as I've ever seen. Single shot, no mag well, just one piece of heavy wall tube with one small port. It came with 3 action screws. It has always been way more accurate with the middle one left completely out.

    Thanks for the list of torque recommendations.

    Fitch
     
  11. meatyrem

    meatyrem Well-Known Member

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    Thanks JE,

    I was just thinking about this today, and got my answer. I was wondering though, what about standard glass bed without the pillars? Is that any different from the torque specifications with the pillar bed?
     
  12. NesikaChad

    NesikaChad Well-Known Member

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    Question:

    What do you base your guard screw rates on? Was their a chart somewhere?
     
  13. J E Custom

    J E Custom Well-Known Member

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    Sorry to take so long to get back with you, I just saw where you added a post to it.

    I got my torque specs from a SAE chart on high grade screws because it is designed to prevent
    failure for the screw. It realy has nothing to do with the use. If a screw fails to meet the needed requirements then you should go to the next size larger.

    In the case of the action/guard screws 65 inch pounds is max for the action not the screw
    and in many cases less is better.(This is the reason I normally start at 35 to 40 inch pounds).

    All values are based on a minimum of 5 threads of engagement or more.

    In most cases, the scope bases and rings fall within the SAE guide lines and are included with
    the bases and rings.

    J E CUSTOM
     
  14. NesikaChad

    NesikaChad Well-Known Member

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    Reason I asked:

    I was faced with this back in 2004. I have a friend in the Seattle area who's an ME. He put me in contact with a colleague of his who's sole job in life is developing fasteners for airplanes.

    He was kind enough to work up a full evaluation based on an assortment of fasteners I sent him. Some were from Brownells and stuff made in house.

    After all sorts of testing he wrote me a full report on this.

    40lbs. No more, no less. More yields the threads. Less doesn't do the job.

    If it takes more than 40, something is wrong. I'd start with the stock.

    The issue lies in the loading on the thread flanks. A screw is a spring for all practical purposes. Your putting the fastener under tension so that it pulls the receiver into the stock. If the load exceeds the capacity of the threads, it will yield and the tension erodes. Not necessarily all at once either. The loading also needs to deliver a sufficient amount of friction so that the fastener stays put. Especially when subjected to vibration. Surface finish has a lot to do with this too. So does the class of thread but I don't get too overly concerned with that part. It is just a dumb guard screw after all. I'd have to dig up the paper, but if memory serves me correctly, 40lbs delivers something like 1600lbs of tensile load. This loading has to be factored based on the root diameter of the fastener. To put this in simple terms. Imagine a bolt measuring an inch in outside diameter. If we were to put some sort of ridiculous pitch on it that resulted in the minor diameter measuring at a 1/2" we couldn't generate calculations based on the outside diameter. The bolt would fail. Pitch and flank angles also plays into this but that's getting really silly.

    Keep in mind also that 40lbs,50, or 60 is sort of a misguided way to do this stuff. Friction will skew the desired result. A screw made from 303 series stainless is quite gummy/sticky compared to one machined from 4140 heat treat. Stainless fasteners in stainless actions only accentuates the effect. Lube on the threads may help some. If we can grease up a barrel tennon, stands to reason you can grease the guard screws. don't forget under the head of the screw also as it has quite a bit of surface area as well. This is one reason why in auto racing things like rod bolts aren't torqued anymore. They measure the elongation of the fastener when it's placed under load. The "stretch" has been calculated to deliver the appropriate amount of tension to ensure the rod cap stays put. Torque to yield fasteners kinda fall into this realm too.


    I've used 40lbs for at least 8 years now. Never once has it failed me. I spent 3 years in Iraq as a security contractor. I was also the chief armorer/firearms instructor at the US Embassy in Baghdad. I bring this up because I heard all sorts of rumors about M40's having issues with zeros.

    Guess what the Marines preach? 65lbs.

    I always wondered if that had something to do with it.


    Take it for what its worth. Just thought I'd share that.


    C.


    Chad Dixon
    Owner/Gunmaker
    LongRifles, Inc.
     
    Last edited: Oct 25, 2011