Scope "shimming"

SksA1

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i never heard of this method before my buddy was talking about it for the Weatherby 30-06.

Why is this nessesary and should all scopes be shimmed?
 
It's only needed if you have to dial your scope far to one end of the turret to get the scope zeroed.
Some say to never do it, but IMO it's necessary sometimes to avoid damaging your scope.
 
There was a pile of Vanguards that needed shimming. Haven't seen one for awhile though.

If you can put a straightedge across the bases and see the sky on the other side, shimming may be in your future.
 
Suggest you read up on Korth Group or Leupold website. It has some good explanations on the topic.

Here is what I learned. Drilling scope holes perfectly in line with the bore center line is rather an art. Mass produced items may not meet this "art" definition.

Shimming may be an option to adjust for vertical alignment. I have used shimming under the rear base on a couple actions. Also you may need significant horisontal adjustment.

The goal is to keep your scope centered because it gives the best optical picture and provides you maximum adjustments. First you either optically center or mechanincally center your scope adjustments. Then you can bore sight to see if you need to shim. For example, if you see the recticle well above the target say at 25 yards (when looking through the bore) what you need to do is shim only the rear base. Also, it is important to consider windage adjustable bases (leupold style) to account for the errors in drilling holes in relation to the bore center line. The best way to reduce stress in the scope when doing this is to use burris zee rings with inserts. You can also play with vertical using those rings as well.

If you do not need to adjust in the field then most of todays lower end scopes (such models provide a lot of adjustment) and will provide enough adjustment to get on paper to sight in. The cost is perhaps less than optimal sight picture and reduced ability to dial in when out in the field. Hope this helps.

Elky.
 
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It should never be the scope you are shimming.. it should only involve the bases... unless the scope rings are Burris Signature rings where you can buy the inserts... you should not try and shim a scope within standard rings because the shim would reduce the inside diameter of the ring where the scope must fit... result - the scope tube must distort...
 
Yup, the posi align signature zee rings have inserts. They help self align the scope without stress. The inserts normally provided offer no offset. You need to purchase the 10 thou offset inserts separately to achieve similar result as shimming under the bases. Another great option where you are having issues.

So to be crystal clear. If you are considering shimming the bases the shims must only be placed between the bases and receiver. As always, it is good to reclarfy such issues so you wont damage your valuables. Thanks for the valuable clarifications Guntech.
 
If you are going to shim one of two separate bases for vertical adjustment, be aware that now your rings are not on the same plane and will need lapping to prevent severe ring marks on the scope and I really don't think that much lapping on both the top and bottom of rings is a great solution. Shimming a one piece base I would think does not present this problem. The Burris Signature rings are a much better answer to this.
 
Can weaver rail style bases be shimmed? Only style of shims I've ever seen wouldn't really work on that.

Any base that is screwed on can be shimmed between the base and the action.

Sometimes the bases require bedding to the action. This can align the bases perfectly with the rings if it is done properly.
 
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