How to Measure Mounting Length of a Riflescope

By Polona Kraner Jul 31, 2018

Welcome to Optics Trade debates. In each episode, we talk about a different topic and try to answer the most common questions we receive about it. Today, we are going to talk about measuring the mounting length on a riflescope.

Different manufacturers measure the mounting length differently. We at Optics Trade decided on one measurement which we use in our store on all riflescopes.

The measurement that we use starts at the end of the eyepiece and ends at the beginning of the objective bell. The measurement includes the part on which the turrets are mounted.

If the scope has a rail, we measure the mounting length from the beginning to the end of the rail.

The longer the mounting length is, the easier it is to mount the scope so that the user will get the correct eye relief. Eye relief is the correct distance between the scope and the eye. Eye relief is about 90 mm on most modern scopes.

If a scope has a long mounting length, it will easily achieve the appropriate eye relief with any ordinary mount.

A scope with a short mounting length needs to be mounted with a special mount that can extend. The first ring is usually extended backward in order to achieve the proper eye relief.

In some cases, the mounting length is so short that the only usable mounts are the ones specially made for specific scopes.

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Explanation of the term on our website:

Mount length is a length of rifle scope tube where ring mounts can be clamped on (see the picture below).

Mount lengths of the tube on rifle scopes are different due to the length of objective and ocular length and sizes. Wide angle type rifle scopes have longer mount length, due to the front side of the rifle scope has a tube till the end.