Shimming A Scope

Shimming a scope is done when a scope is maladjusted, or cannot adjust any further in order to send your shot on target. Some may try shimming a scope by adding bits of thin material inside the scope’s mount rings or even under the mounts themselves, where they connect to the gun. Other than that, a scope may fall just short of the aim point even after adjusting as much as possible, and you want a little play in the adjustment parameters for simple corrections, so shimming a scope can be used to this end as well.

But what’s a shim? Well basically, a shim is a piece of flat… well, anything. Something that you use to adjust something else that is just off the mark. For instance, that annoying wobble that the table does when you and your friends are just trying to play a decent game of poker – what do you do? You fold up a piece of paper a few times over, or a ripped off segment of pizza box, or whatever is handy, and you stick it under the short table leg in question to put an end to the wobble. That’s what a shim is, and shimming a scope uses the same basic idea.

Now if your shot is falling below the mark, shimming a scope to move the rear of the scope up, raises the strike of your shot. To make the strike of the shot go down, the front of the scope is raised instead. This may sound overly simple, but it’s very effective. The one drawback of this, depending on your type of scope mount, is that raising the rear of the scope by shimming below the rear mount can only be done well with a two piece mounting system. If you did this with a one piece mounting system, it would make it difficult for the dovetail to grab hold of the grooves on your rifle.

The practice of shimming a scope may fix the problem, but don’t do it too much or you can bend, distort, or even break your scope tube. The rings holding the scope are made to align with each other so that the tube of the scope is held tightly and straight. When you raise one end of the scope with a shim, the tube of the scope will be bending under stress. A few thousandths of an inch may be somewhat negligible, but any thicker than that will cause enough tension to distort the alignment of your scope. A very slight loosening of one of the scope ring caps can slightly allow for a thicker shim if need be, but don’t overdo it. Shimming a scope may prove helpful in a pinch, but when all is said and done, adjustable scope mounts are a much more permanent solution.

 

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