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Which base gets the shim & how thick?

Discussion in 'Rifle Country' started by NoAlibi, Jul 20, 2010.

  1. NoAlibi

    NoAlibi Well-Known Member

    Several years ago I set up a Anshutz 64 with a Leupold fixed 12X scope on two piece Leupold bases. I used to shoot it in my basement and at a 25 yd indoor range. The scope is equipped with a Leupold screw-on lens to adapt it to close ranges.

    I used all the up adjustment on the scope which put the cross hairs in the exact middle of the bullseye and that’s where all the bullets go. So, no problem at 25 yards.

    Now I want to shoot a regulation silhouette match with it and I ‘ll be needing some more up adjustment so the questions are:

    1 - Under which base does the shim go?

    2 - How thick should the shim be?

    Thanks in advance for your help.....Doc
    Last edited: Jul 20, 2010
  2. hoghunting

    hoghunting Well-Known Member

    The rear base needs to be raised, but if the rear base is higher than the front base, you will be bending the scope tube. The easiest and safest fix is using Burris Signature rings with the offset insert kit. The inserts will align the scope to the barrel without stressing the scope tube.
  3. Maverick223

    Maverick223 Well-Known Member

  4. NoAlibi

    NoAlibi Well-Known Member

    One answer raises another question...

    hoghunting - I've heard of others putting in a shim, but I never gave any thought about the tube being stressed. I can't thank you enough for posting your answer; you may have saved me from permanently damaging my scope.

    Maverick223 - That was a VERY helpful chart and I appreciate your response very much too.

    One more question please: I have a ballistic generator, but I don't have any values to plug in for .22 LR. Do you or does anyone else have an answer or a link so I can find out what the bullet drop at 110 yards is with a 25 yard zero?
  5. Maverick223

    Maverick223 Well-Known Member

    FWIW, I have never heard of, or personally experienced, any damage resulting from a couple small shims. Damage usually results from someone that is overzealous and/or puts shims under the scope (in the ring).

    Here is some ballistics information, and here is some .22LR specs, that you may find helpful, though the former is not computed at the same zero. Below is the data that I received when running a popular .22LR load (Wolf Match) through my ballistic software:

    Last edited: Jul 20, 2010
  6. NoAlibi

    NoAlibi Well-Known Member

    Maverick223 - The ballistic coefficient was the missing ingredient for my calculations, so now Im good to go - thanks for taking the time to dig up all that info for me.

    God, I love this site!!!

    PS - I’m aware that the folks here ARE the site.
  7. Maverick223

    Maverick223 Well-Known Member

    NP, NoAlibi, glad it helped.

  8. hoghunting

    hoghunting Well-Known Member

    Shimming may not damage the scope, but if one ring is higher than the other, the tube will be stressed. The elevation and windage adjustments could be off or the zero moves at unfortunate times. When the stress is relieved, the scope could very well act normally.
  9. Uncle Mike

    Uncle Mike Well-Known Member

    Well it is pretty simple...if you shim the bases or rings, and tighten the caps, you WILL bend your scope! It may be ever so slightly, and it might work(for now), but none the less, you are bending the tube....don't do it!

    The tapered base(s) are the correct rout to take, BKL(Pyramid Air) has tapered aluminum 22 and airgun bases and ring-sets.

    The Burris Signature rings will allow the same result as a tapered base but they are a royal pain to get dialed in and they still put a small amount of 'stress' on the tube, which will be magnified during broad temperature changes.

    The Burris Signature Ring inserts are better suited for use with scopes that utilize 'thicker' wall tube material.

    If your going to shim, NEVER shim a TWO piece base, for obvious reasons. Shimming a one piece base will work without damage to the scope but the base screws are 'bent' upon installation of the base onto the receiver, which isn't a real problem if your not planning on removing these screws...also, I have seen the heads of screws pop off from doing this when the temperature became really frigid!

    Tapered bases or ring-sets, the way to go!
  10. Maverick223

    Maverick223 Well-Known Member

    In hindsight you guys are right. All the shimming that I have done, and recall having seen were with 1-pc. bases, that is why no damage resulted. Considering that you have 2-pc. bases, I would heed hoghunting and Uncle Mike's advice and not shim those bases.

  11. NoAlibi

    NoAlibi Well-Known Member

    Maybe there’s another way to fix the problem.

    The gun, scope, bases and rings are standard equipment. So why am I having this problem?

    Before I shim I’m going to switch the bases (rings attached) with each other and see what happens.

    If everything remains the same then I would think that the receiver is not parallel with the barrel.

    If the problem reverses itself then it's either the bases or rings. The next step would be to switch the rings around. If everything remains the same then I would think that the bases are the problem. Do I have this right?

    If I can isolate the problem to the rings or the bases, then maybe I can get Leupold to replace the defective part(s) and not have to shim or buy special rings or bases.
  12. Uncle Mike

    Uncle Mike Well-Known Member

    I hate to say this...but you can 'raise' your scope higher off of the receiver for those close in targets, higher rings.

    Play with the height of the rings until your on target.
  13. Maverick223

    Maverick223 Well-Known Member

    I think he needs to go the other way...scope down (or POI up). Honestly the best solution is probably a scope with a greater adjustment range.


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