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Scope Shimming or Adjustable Mounts?

Updated: Oct 7, 2023

Why you may not have enough adjustment

Not got enough elevation adjustment on your scope? Your fellow shooters may have suggested scope shimming or perhaps even adjustable mounts. One is a quick and low-cost fix, the other is a professional solution but may be tricky to get to grips with; but which is right for you?


Right off the bat let's get something straight... the requirement for scope lifting whether that is shims or adjustable mounts is NOT a sign that your gun or scope is faulty!

Scope Adjustment
Manufacturer Scope Adjustment Limitations

Every manufacturer must design for the mass market, this means that the scope you may have is designed to target as large an audience as possible. So adjustment parameters of the scope are designed to operate within a window in which pro-level weapons and budget guns share. This translates to long-range and short-range weapons respectively. If a manufacturer decided to make a scope that suited both needs, sacrifices in features must be made or costs would increase.


Get the right scope for your use

To keep costs down, manufacturers develop generalised scopes that work with a multitude of calibres, ranges and requirements; opting instead to produce adjustable mounts for the ends of the spectrum of users. This is why it is important to understand the requirements of your scope. A higher magnification scope can lead to false ideas of your rifles performance "I can see the target, I should be able to hit it"

Scope magnification to target size relation at 10 meters
Scope Magnification at 10m (Based on 17cm target at 20x power)

A rifle designed for long-range shooting may have an inclined barrel (or declined rail) to build in a compensation for the arc of the projectile. So when you pick one of these rifles and shoot a lot shorter than the manufacturer intended it appears that your scope will not adjust high enough. This is true of the other way around, where a rifle designed for shorter ranges is pushed out beyond its designed range the scope will appear to not adjust low enough.


To Shim or Adjust?

The solution is to lift the scope; this forces you to compensate by lifting or dropping the elevation of the barrel as the scope dictates the elevation of the rifle based on the grip you have on your rifle. This can of course be done with either manufacturing (or purchasing) shims or purchasing adjustable mounts. The choice of which one you want to do is down to you. The best we can do is outline the pros and cons of each.

Scope Shimming/Adjustment
Scope Lift Effecting Impact Point

Shims

Shims are normally thin pieces of aluminium or plastic that are used to pack out your scope either below or above the tube to change the pitch of the scope.

Pros

Cons

  • Cheap

  • Easy

  • Quick

  • ​Can add unnecessary strain to the scope

  • The scope may slip during recoil

  • Over time the shims may need to be replaced

Shim Types

A DIY solution that we see regularly is the use of aluminium drinks cans being used as this is thin and flexible to make your shims without damaging anything as well as being virtually cost-free. There are purpose made shims that can be purchased to achieve the same result with a more professional finish.


Shim Positions

The positioning of your shims dictates how your impact point changes. Rear-Lower and/or Front-Upper shims lower your impact point, whereas Rear-Upper and/or Front-Lower heighten your impact point.


So if your gun is shooting lower than your scope will allow, you need to lower your impact point by lifting the rear of your scope up.


The thickness you may require can be hard to determine, however, most drinks cans walls are about 0.1mm thick meaning a single piece can shift your scopes impact point nearly an inch at 25m, if you need more you can add more shims, but ensure they are cut in decreasing sizes to avoid a pinching effect.

Adjustable Mounts

Most scope mount manufacturers will sell adjustment mounts or elevation altering mounts (MOA rails) that can be used to alter your impact point depending on your choice of shooting. These normally have a linear amount of adjustment, that quite often include attaching your scope to your mounts then unlocking the adjustment to allow tiny adjustments whilst reducing stress on the scope.

Adjustable scope mounts vs shimming
Shims can cause stress on the scope when overpacking

Pros

Cons

  • ​A lot of adjustment

  • Does not stress the scope

  • Even grip on the scope

  • ​Can be difficult to use

  • Over adjustment is common

  • Can be expensive

Conclusion

Your requirements and options differ person to person. However, for us we would always suggest contemplating if the solution aligns with the cost and its outcome. For instance, if you are a casual backyard plinker, adjustable mounts may not be ideal for you. However if you enjoy shooting and are planning to take it pro or it is your main hobby, then perhaps adjustable mounts are worth it to you. If not, a shim works perfectly well in lesser demanding environments.


Think we missed something?

Let us know in the comments below.




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