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Shims for a Scope

Sometimes when you mount a scope – something just aint right and you can’t get the scope aligned properly to get it bore-sighted.  Slight errors in the making of the base or rings or something…  Many reasons… but the result is that to get the scope bore-sighted right, you have to shim the scope.   Don’t panic.  And don’t go off and order some expensive Shim Kit.  And don’t use Paper shim.  They compress and get thinner over time.   You don’t need to spend any money… well, maybe 75 Cents at most.  You can make your own Shims.   It’s easy to do, and I do it all the time.  I am a professional, and I’m telling you – you can do this at home.  It’s Ballistic Science, but it’s not Rocket Science. All you have to do is to make some Beer Can Shims.

Now, they are called Beer Can Shims, because that’s what they were called when I learned of them… at Ft. Benning.  They called them that, because that was what they used.  They specified the use of Bud Light cans, but you can use Miller, regular Bud, Guinness, or any variety… for Mormons, you can use Mt. Dew, Coke, Pepsi, Full Throttle, Monster… because really, the brand is not important – but a Benning the SOP was Bud Light.  Just sayin.  Personally, I prefer Rockstar.

Pro-Tip: Wash the can out with hot water and dry it.

You use some shears, open the can up, and cut off the tops and bottoms.  Trim up sheet and section it, then cut it into strips.   The width and length are up to you.  1 inch tubes will use shorter ones than 30mm tubes.

If you make enough, you can go all Rip Taylor with them.

When you put them in the ring, under the scope, check the bore-site to make sure that you get the right amount.  Don’t use more than 4 shims.  If you need more than 4, you need to rings and bases or there is something wrong with the gun.  Typically I use no more than 3. When stacking them, but down a long one, then a shorter one on top, then a shorter one than the last.  You don’t want to shim the sides, just the bottom.  If you are shooting too low, shim the Rear.  Too high, shim the front.  Simple stuff… unless you get it wrong.

 

7 Comments

  1. 05/03/2011    

    What about the Burris ring inserts? Have you used any of those? Sure they’re more expensive(by a long shot) But I’ve used them with excellent results, and as an added bonus, they don’t mark up the scope tube at all.

    • 05/04/2011    

      Those are part of the Burris Signature Series… so they work well if you are using the Signatures.

  2. SquirrelCutter's Gravatar SquirrelCutter
    05/04/2011    

    Zen and the Art of Motorcycle Maintenance.

    Look it up.

  3. Brian Parramore's Gravatar Brian Parramore
    05/06/2011    

    I’m a 35 year machinist and I have shimmed many many things with aluminum cans. The material is about .001 thicker at the bottom of the can than at the top. You can use that difference to make fine adjustments in shim thickness.

  4. george's Gravatar george
    11/28/2014    

    I never shim in the rings. always shim under the base. tin foil works well as well as aluminum can material. foil is easy to start screw holes in. try 3 layers of foil to start.

    • MadOgre's Gravatar MadOgre
      11/28/2014    

      There are so many reasons that shimming the base is a bad idea. But I’ll start off with Recoil shearing the tiny screws that are now no longer going as deep into the receiver as they should.

      • Ed Rylander's Gravatar Ed Rylander
        02/15/2015    

        Mounting screws and receivers are always manufactured at least 0.01 deep/long to allow for this very very common needed correction, most parts sellers have “shim kits” to do just this.

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