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 discuss mounting dimensions or dimensions associated with riflescope mounts.
There are two measurements which are we commonly asked about, BH and KR. BH stands for build height which comes from the German word Bauhöhe. It’s the distance between the upper part of the rifle and the bottom part of the tube.
In case you have a complete mount (like the Recknagel pivot mount) the bases are calculated in the total BH height of the mount. It takes into account the height of the base, the height of the front foot and the ring all the way to the scope barrel. You need to take the base and all other parts into account when measuring BH.
If you take a look at a Picatinny monoblock, the BH of a Picatinny is not calculated in the total height, you have to add it to get a BH. For example: if BH of a Picatinny rail is 7 mm, you have to add 7 mm to the BH of the monoblock to get a total BH.
If we are comparing a mount from Spuhr to a Recknagel mount, we always use the same way of measuring for all the brands.
On our webpage, BH is measured from the lower mounting surface of the mount to the upper, even with Spuhr (normally measured from the Picatinny rail to the center of the rings).
In the case there is a rail on the scope, the BH is the measurement from the rail on the rifle to the lower part of the rail on the scope.
KR means extension, it comes from the German word Kröpfung. It’s measured from the middle of the screw (where the mount holds the rifle) to the end part of the front ring. And it is also measured from the middle of the key to the end of the ring on a pivot mount.
In most cases, the KR or the extension (at least on all hunting rifles) goes backward, so we can get the scope back enough to get the proper eye relief.
AR rifles also have the extension but it goes in the other way, forward. We measure it from the middle part of the front screw to the end part.
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Explanation of the terms on our website:
BH stands for Bauhöhe (ger.) which means overall height. It is measured from the mounting surface of the rifle to the lower surface of the riflescope’s tube.
KR stands for Kröpfung (ger.) which means extension. This is the distance between the mounting surface and the front ring, measured horizontally. If the ring is exactly above the mounting surface, the KR is 0 mm.