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shimming a scope

How to Shim A Thermal Rifle Scope

You may have knowledge of shimming from a construction perspective, shimming a door or window. Did you know it is possible to shim the scope of a rifle? It is not the most suitable fix, but it acts as a temporary solution. You might have to use this method if your scope becomes badly knocked out of alignment before a search or, in the event of argon shooting, you are up against a case of barrel droop.

What is Shimming? Shimming is when you put a thin piece of material between the scope and the back scope ring to raise the elevation to not adjust to the scope modifications and properly align your scope with the barrel. Follow along with this manual to learn precisely how to shim a rifle scope.

Some Things You'll Need

Mounted Rifle Scope -- Shimming is sort of an emergency fix, so if you're using this technique, you likely already have your scope mounted to your rifle. When it is not, then a better way to fix an altitude alignment problem is to use flexible scope rings or a unique elevated mounting base. Shimming can harm your scope, so it is not the best nor long-term alternative.

Hex Wrenches -- you'll want to have these to remove your scope from the scope rings. It's probably a great idea to take some of them on your hunting pack or rifle case just in case of a crisis.

Very Thin, Sturdy Material -- many substances will work in a pinch for shimming. The key is they need to be thin—thin, aluminum pop cans, laminated cards, business cards, etc.. The material type does not really matter. It can be plastic, aluminum, or paper. Something as thick as a credit card is far too thick. Try to keep it quite thin and stiff though pliable.

Scissors -- Ideally, you need some scissors to cut your material to the appropriate size to match between the scope and back scope ring.

Small Level -- Another tool you might choose to carry in your hunting package just in case. This is to analyze that the scope is re-mounted correctly and level when you're finished shimming.

The Way to Shim A Rifle Scope

how to shim a scope

Remember that this is simply a crisis or temporary fix. You really don't need to have many shim layers if you can help it since it will lead to damage to your extent and make it more unstable. A couple of layers just is best. If you want more, make sure to reduce your shims in size to better cradle the extent and lineup to another shim when layered.

Step 1 -- Pick And Cut Your Shims

Whatever you wish to use for shims or have available. Aluminum pop cans work excellent and shape the scope rings quickly. Cut them out small enough to fit smoothly into the bottom part of the rear scope ring. If you're using more than one, cut the shims somewhat smaller every time so that they will line up together when layered and cause minimal harm to the extent.

Step 2 -- Eliminate Scope From Scope Rings

Take out your rifle bolt. Then eliminate the scope from the rings using your hex wrenches. Have the bottom section of the rings attached to the rifle.

Step 3 -- Place Shims

Place your shims with the biggest inside the back scope ring and slowly layer accordingly. You should only need two shims. If more is required, ensure you know approximately how far the shims will change your shot each 100-yards.

Step 4 -- Re-mount The Scope

Smoothly place your scope back on the rings and shims and properly tighten back down. You need to tighten these down gradually and evenly not harm your scope when it pushes back on the shims. Make sure that the scope is nice and tight so it will not move around because of recoil.

Step 5 -- Check For Level

Double-check your level to be sure that the scope is level and one side isn't tightened more than the other—your desire your shims sitting completely.

Step 6 -- Sight-in

Now that it is all back together, you need to check fire and zero your scope to ensure that the shims work for you. If it is possible to zero the scope, success! You're ready to hunt. Otherwise, repeat the steps adding fewer or more shims as needed. This is simply a temporary or emergency fix, so make sure to find the appropriate equipment to correctly fix your mount whenever you can.

Common Questions

Why would I want to shim my scope?

Occasionally, your scope might be knocked very far from alignment anyhow. You wouldn't necessarily have the ability to resolve this correctly if you're, for example, traveling for a hunting trip or contest. Another reason can be for barrel droop on an air rifle. This is the point the barrel really sinks and leads in another direction of the reticle.

How many shims do I want?

This is dependent upon your shim material depth. A pop can shim include about three to four inches each 100-yards per shim. Other substances may have minor differences but should be somewhat similar as long as you do not use something too thick.


You now know the way to shim your rifle scope a bit. We hope that this guide was useful to you in gaining an understanding of doing this method, but we expect you to not actually have to use it. Needing to do this implies that something is screwed up, and again, shimming could even damage your scope. But if you do end up with this manual, we hope it saves your search or competition! Damaging or not, this may be the specific method needed to quickly fix your rifle and get you back on target.

About the Author Rob Carson

I work in commercial construction, in Dallas, TX.

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