Review of the Spuhr ISMS scope mounting system.
The first time I saw a SPUHR ISMS, I thought what an ugly looking scope mount it was. I bought one to try it and was immediately impressed when I opened the box, and it kept getting better from there. The scope mount while odd at first is so exceptionally made and so well thought out that it deserves praise that far overcomes any of the initial skepticism I had. The flat sides allow you to see the complete parallax turret when behind the rifle, this is a great improvement over traditional scope mount systems that I never would have thought of designing the mount this way.
View showing the clearance between mount and parallax turret
The underside of the mount has multiple recoil lugs to fit into the rail for recoil management and also the five mount screws, very robust. This mount also has a built in level which removes the need to buy a picatinny rail mount level and it cleans up the lines of the rifle.
Look at how bright the level is, makes using it easy.
The ISMS is amazingly robust for an aluminum mount, each wide ring top cap is held to the base with six screws and the base is held to the rail with five screws, very solid. This mount is also threaded in multiple places for additional attachments for cosine indicators, lasers, accessory sights etc.
The mount on this rifle is the Spuhr SP-4001 that was bought at the link below as it was the best price we could find. The mount has not shifted or had a less than solid point of impact. It is rather astounding how well this mount is made.
Spuhr SP-4001 34mm Ring Picatinny Mount, 0Mil/0MOA Cant, 1.18” Height
- Ring size 34mm, Cant 0 MIL/0 MOA, Height 30 mm/1.18″, Length 121 mm/4.76″
- Milled out of one billet of 7075 T651 aluminum
- 45 degree split of the rings gives better view of the turrets
- Patent pending solution for indexing the rotation of the scope, using an included tool/gauge to index the scope correctly to the mount and gun
- Built-in level
The Spuhr SP-4001 has 0 MOA built into as the AI has cant built into the rifle base on the rifle. Spuhr does however make many different cant’s, tube sizes and heights. See the attached the PDF for reference in making the selection that is right for you.
In the instruction manual they say to use their tapered alignment shim to mount the scope level to the rings. We tried it and it works ok, I still prefer to use the feeler gauge method as it is most certainly more precise. This is done by using a good undamaged set of clean feeler gauges. You mount the scope in the base with the ring caps on but only finger tight. Then take the feeler gauges and find the thickness needed to be close to a slip fit between the bottom of the erector tube and the scope base. Keep adding shims until you have a snug fit but not enough you are deflecting the scope. Slowly criss-cross tighten the cap screws checking that you do not have too thick of a shim beneath the scope and that you can still slide the shim out from under the turret block. Continue torqueing the screw with the torque screwdriver, you can use one of the ones mentioned in the torque wrench article.
Feeler gauges between turret body and flat of mount
When this is done you will have an erector assembly that is perfectly parallel to the scope base. This is important because as you shoot further and further out you are dialing the elevation on the turret. If the turret is not exactly parallel to the rifle you will also accidentally be dialing windage as the reticle is not only taking a vertical path but also a slight horizontal travel too.
We have found this to be a great scope mount and well worth the investment, you won’t be disappointed.
Two thumbs up.