# Determining Correct Scope Base Angle By Robert H. Thompson

Discussion in 'Technical Articles - Discussion' started by ADMIN, Oct 11, 2009.

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This is a thread for discussion of the article, Determining Correct Scope Base Angle, By Robert H. Thompson. Here you can ask questions or make comments about the article.

2. ### ZebDemingActive Member

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Sep 29, 2008
Great article! Great way of describing how to figure out how much shim to use. I've used the formula: TAN (angle of base) * length between centers. A little more complicated as it requires a scientific calculator and I had to relearn myself on high school trig, but it works. Remember that it requires you to keep everything in degrees so 30 MOA would be .5 degrees.

Zeb

3. ### HUAINAMACHEROWell-Known Member

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Oct 16, 2008
Robert,
Thanks for the teaching, great article. This information should help many of us with future projects.

4. ### zp3designMember

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Aug 18, 2007
Thanks you guys.

Mainly what I was hoping to do was help others with angled scope bases and also with understanding MOA.

Bob

5. ### BuffalobobWriters Guild

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Couple of points to remember.

If you shim the rear base much more than 20 MOA then you may need longer rear base screws. You have to make sure they are not too long and hit the bolt. If you try to use too short of screws you risk stripping the threads when they pull loose.

Before you shim a scope check the receiver to see if it is level to begin with. Many are not square and you will begin with some positive or negative angle even with a flat base. This must be accounted for in determining the amount of shim needed.

6. ### 1mspicerNew Member

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Jan 5, 2011
What did you make the shims from?

Last edited: Jan 15, 2011
7. ### zp3designMember

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Aug 18, 2007
Brass shim stock, I think it was 0.010 inches or 0.25 millimeters thick. Here in America it is readily available from industrial supply houses. I purchased a pack of assorted thicknesses many years ago.

zp3