Scope Mounting Height Guide

The list below gives the actual height for each mount, measured from the top of the action to the underside of the scope tube.  This height is commonly known as BH* and is very useful when calculating the height required for a scope mount.

*BH, abbreviation of the German “Bauhohe” = “overall height”

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Mounting Height Calculation

To calculate the required mount height, measure the diameter of the objective lens of your scope and divide by 2 to give you the radius. If your scope has a 56mm objective lens, the actual measured diameter of the objective lens is probably around 64mm for example. Divide this by 2 gives a radius of 32mm. (Measurement (a) on the diagram below)

The radius of your scopes mid-tube, which is the diameter divided by 2. A 30mm mid-tube divided by 2 equals 15mm for example. (Measurement (b) on the diagram below)

The difference between the Objective Lens and the Mid-Tube is the height required of your scope mounts so the scope does not touch the barrel. The calculation is simply (a) minus (b) = Minimum BH to Top of the Action.
In this case 32mm minus 15mm = Minimum BH to Top of the Action of 17mm.

However, most scopes sit forward of the action and over the barrel. The barrel on most hunting rifles will be lower than the top of the action. Depending on your rifle and barrel, you can potentially achieve a lower mount by measuring this gap. If you place a straight edge on top of the action projecting forward over the barrel. Measure from the underside of the straight edge down to the barrel at the point where the objective lens will reach. (Measurement (c) on the diagram below)

Take this measurement (c) away from the height you already have and add 1mm to ensure the objective lens does not actually touch the barrel. For example, the difference between the top of the action and the barrel is 5mm. You already calculated the Minimum BH as 17mm, so you take 5mm away, leaving 12mm. Don't forget to add 1mm for clearance, and you now have a height of 13mm. From the table above you can see that the 30mm Med High is exactly 13mm. So this would be perfect.

The drawing below illustrates the points to be measured
Calculation to use: a - b - c + 1 = Minumum BH
Using the figures below: 32mm - 15mm - 5mm + 1mm = 13mm

If you have lens covers mounted on your scope remember to include this when measuring the diameter of the objective lens. If you change your scope from Summer position to Winter, your scope will sit further back over the thicker part of the barrel and this will reduce the clearance under the objective lens. For this reason, it is recommended that all measurements are taken assuming the scope will be in the rear Winter position.

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