Will I loose my 100 yard Zero?

Discussion in 'Long Range Scopes and Other Optics' started by scsims, May 16, 2008.

  1. scsims

    scsims Well-Known Member

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    Have a Nikon Monarch 6.5-20x44mm scope on my Rem 700 308 with Leupold mounts and bases. I have a shim that Leupold has sent me.

    I haven't sighted in the rifle or installed the shim yet. The scope only has 38 MOA of vertical adjustment so I thought the shim would help me get out to 600+ yards.

    If I use the shim supplied from Leupold will I still be able to zero at 100 yards?
     
  2. Eaglet

    Eaglet Well-Known Member

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    Give us more info about the shim. Where is it for? How thick is it? What is the distance from the center of the front ring to the center of the rear ring? What is your scope height, from center of barrel to center of scope? That would help.
     
    Last edited: Nov 24, 2008

  3. davewilson

    davewilson Well-Known Member

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    Eaglet is correct with his info.just take some measurements and triangulate the angle. we're assuming the shim will go under the scope on the rear mount, so, in very general terms, figure about one MOA for every thousands of shim thickness. i've heard some that use the Burris rings with the offset inserts that this is about what it works out to.
     
  4. scsims

    scsims Well-Known Member

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    OK I sighted in the gun today with no shim. It shoots good for Rem 180grain Corelokt factory loads. best groups were well under an inch.

    With it sighted in I only have about 2 MOA left of up adjustment. Seems alittle odd but that's what I have.

    The shim that I have from Leupold is a 20 MOA shim. My scope is 1.5" above the center of the bore and the rings are 3.5" apart.

    I think the shim will work, is it OK to just install the shim under the rear base?
     
  5. Eaglet

    Eaglet Well-Known Member

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    scsims,

    With the new information you provided here are my conclusions:

    ArcTang(0.020/3.5) = 0.3274° = 0°19' = 19 MOA's
    That means (assuming you zeroed at 100 yards) that with the shim you could have your "0" at 100 yards and have 21 MOA's left for vertical adjustment. At 3000 ft of altitude, using the factory bullet you mentioned, you would need 16.75 moa. I would say it would be about the most you want to push it, maybe up to 19 that would allow you to shoot at that altitude at about... 19.25 moa would put you at 650 yards.

    This is what's bothereing me. I have never used shims before and I would think that if you base is a single one piece base, a 0.020" shim would be alright to place at the rear of the base; but if you have 2 separate pieces as base I would not use shims. In my mind you would mess up the scope. Would be putting too much stress on it.
     
  6. davewilson

    davewilson Well-Known Member

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    yes, put it under the rear base. but i would wrap some tape around the scope where the rings make contact to protect the scope with the slight amount of "misalignment" this is where the Burris signiture series rings are schweet! a 20MOA shim for your setup will be about .020 thick.
     
    Last edited: May 20, 2008
  7. scsims

    scsims Well-Known Member

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    What kind of tape would you use?
     
  8. Varmint Hunter

    Varmint Hunter Well-Known Member

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    Do yourself a bif facor and do I of 2 things:

    1. Get a properly manufactured taper base and forget about shims.

    2. Buy a set of Burris Signature rings and use the .010" or .020" offset inserts. They make for a very clean and adjustable set-up. They wil also avoid appling detrimental stress to the scope tube.

    Just my 2 cents
     
  9. jwp475

    jwp475 Well-Known Member

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    I agree, using shims with a 2 piece base will definitely exert undue misalignment stress on the scope tube. Shims under a one piece base is at the very least a poor way to correct for a tapered base IMHO
     
    Last edited: May 21, 2008
  10. scsims

    scsims Well-Known Member

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    Hmm, I was just looking though my spare scope mount drawer and came across a Leupold 1 piece. So what's the issue with shimming a 1 piece base.

    Not as ridged?
     
  11. Eaglet

    Eaglet Well-Known Member

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    Varmint Hunter,

    Jwp475,

    +1
     
  12. ss7mm

    ss7mm Writers Guild

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    I recently had occasion to try and explain to a fella about shimming bases vs. using a new, angled, properly built increased moa base. I ended up drawing it out. I really exaggerated the angles/tilt to try and make it visually easier to understand. Don't know if this will help but it helped my friend to see why he'd be better off buying a new, properly machined base.

    [​IMG]

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    [​IMG]
     
    Last edited: May 22, 2008
  13. Eaglet

    Eaglet Well-Known Member

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    Beautifully explained!!! Good job! That's exactly what was bothering my little peanut head. I could see those holes not matching and I even thought that maybe a little bedding epoxy would help, those bolt holes would still be crooked...

    Good Job!
     
    Last edited: Nov 24, 2008
  14. scsims

    scsims Well-Known Member

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    Ok I get it. I will take my Leupolds back and do the right thing and get the correct set up.

    But I wonder if with a different set up even if I just got a different base and rings with no MOA add in would I get the same results that I have with these mounts.