scope shim suggestions

Discussion in 'Gunsmithing' started by Texas Republic, Mar 18, 2013.

  1. Texas Republic

    Texas Republic Well-Known Member

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    I noticed this weekend while doing load development on my 338 Lapua that my groups all seem to be traveling downward on the target. All of them… After checking out my base, etc.. I noticed these marks on my scope from it moving in the rings. I suspect the reason for the movement is that I have shimmed the rear rings with aluminum beer can. Coke can will not do. Coors original works best.
    Anyhow.. I have shimmed this scope before in the past and it worked fine. Guess my only option is to tighten down more on the screws? I already have them at 20 inch pounds on the torque wrench. I think its inch pounds. I use the wheeler torque wrench.
    The other option of taking the shim out wont work really. Long story..but basically I use the Larue QD lever base on two different rifles and taking it out wont allow my 308 any MOA up hardly. After switching my optics over to my LR308 it worked fine with no movement at all. Just the Lapua moved it.

    Any other ideas to fix this problem?
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  2. highridge1

    highridge1 Well-Known Member

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    I stopped this problem a couple times by rubbing a tiny dab of clear silicone in the rings halves when mounting.Gave a grip on the scope and they stopped sliding
     

  3. Texas Republic

    Texas Republic Well-Known Member

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    Where exactly did you put the silicone at? Between the rings and shim or the shim and scope?
     
  4. bruce_ventura

    bruce_ventura Well-Known Member

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    Texas, how many beer can shims do you have in there?
     
  5. GNERGY

    GNERGY Guest

    Another good product that I have used before was called stick n seal, it is like silicone and super glue in one. Put it between the rings and the scope, just a little and put the rings back on the scope and let it dry. The excess will scrape off with your fingernail or tooth pick and it will keep it from sliding. I had one of JD Jones Contenders that the scope used to slide and that fixed it right up.
    Tarey
     
  6. Greyfox

    Greyfox Well-Known Member

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    I think the use of shims, adhesives, etc. to secure a scope in the in the rings can work ok with low intensity rounds but it is likely that you will have a difficult tiime trying to establish a solid and permanent mount for your scope using this approach with a 338 Lapua. The inertia placed on the scope with this round, even with a brake, is severe and requires a very secure mounting system. It's hard to see clearly, but it also looks like there are some scratch marks on portions of your scope caused by rings not being properly lapped. This could be an indication that the rings are not making complete contact with the scope tube. I think in the end, you may find that a larger surface area, heavy duty ring style like the Nightforce or Mark 4 tactical style rings and bases may be required to keep the scope in place. IMO.
     
  7. bruce_ventura

    bruce_ventura Well-Known Member

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    There are better ways to deal with this problem.

    Inserting a shim between the ring and scope reduces the surface contact at both rings, and generates stress in the scope tube. That's why the scope tube is scratched and the scope slips in the rings. Adding an elastic material like silicone may prevent slipping, but won't remove the stress.

    It would be better to bed the scope in both rings using a rigid bedding material like JB Weld. YouTube has videos that demonstrate this process. Coat the scope tube with shoe polish or furniture wax to keep the epoxy from sticking. Use a small piece of shim in the bottom of the ring. Sandwich the shim in bedding material, place the scope in the rings, and finger tighten the ring screws (5 in lbs or less). Don't bed the ring caps.

    You can add up to 25-30 MOA of elevation this way (three beer can shims). Ring contact will be great, and there won't be any stress in the scope tube.
     
    Last edited: Mar 22, 2013