CHOOSING A MOUNT
We have the world's most comprehensive line of tactical scope mounts; it currently spans about 60 different models of various heights, tilts, lengths and ring dimensions. We have therefore compiled this short guide to help you choose the right mount for your needs.
Picatinny or direct/dovetail mount?
The first question is if the mount should be a Picatinny mount (models beginning with SP or QDP) or a direct attachment mount such as Spuhrs line of ISMS mounts for Accuracy International (SA,) Sako TRG/Tikka T3x (ST,) and Sauer SSG (SS)?
The main reason for using a direct mount is to allow a stronger and lower positioning of the rifle scope. If there is no other need for a Picatinny rail Spuhr generally recommend direct mounts on these rifles.
Please note that both Accuracy International and Sako are now making rifles that have Picatinny rails rather than their traditional dovetails, so make sure you check which style of mount is needed for your particular rifle.
Cantilever or block mount?
Most Spuhr mounts are standard block mounts as these will be the best choice for the majority of rifles on the market. There are some exceptions though…..
AR15 rifles usually require a cantilever mount for a comfortable shooting position, and an AR15 with an adjustable stock will more often need a more extreme cantilever than an AR10/SR25 due to the difference in length of the upper receiver. As such, if your rifle has a monolithic upper we recommend using a standard block mount rather than a cantilever design, as a cantilever will be more susceptible to side forces than a non cantilever design.
The height of Spuhr mounts is always measured from the top of the rail to the center of the scope. In the case of a tilted mount the measurement is made at the back plane of the rear ring.
So which height do you need?
First off you need to know the outer diameter of your objective. Please note that "3-12x56" does not mean that the scope has an outer objective diameter of 56 mm - only that the objective lens is 56mm in diameter. Different scopes have different outer diameters for the same lens diameters and it's not uncommon that different models from the same manufacturer feature different outer diameters even if the lens diameter is the same.
Take the measurement above and divide it by two (2) to get the theoretical minimum height required if the optics will be mounted onto a flat rail that extends to and/or past the objective bell. This theoretical minimum height is theoretical for a reason. If the objective has a 62 mm outer diameter and you choose a 31 mm high mount the objective will be in contact with the rail. You will therefore need to add to the theoretical minimum height to get the practical minimum height.
So how much do you need to add? That depends on your personal preference and on what kind of lens caps etc.,you want to use. Also, if you want to use a tilted mount/base you will need to add additional clearance.
If you intend to mount the optics onto a bolt action rifle with Picatinny base you can often use a lower mount than the theoretical minimum height above. Just subtract the height of the base from the theoretical minimum height mentioned above. Depending on barrel contour you might be able to go even lower. But don't forget toleave some clearance for lens caps and/or sunshades!
Night vision/thermal compatibility
When combining the scope with a clip-on system such as PVS22 or NSV 80, to name a few, the height of the mount is not important. Also the instrument doesn’t have to be perfectly in line with the scope.
If we have an offset of 10 mm in height between the primary optic and the NV clip-on the change in point of impact will be 10 mm on 100 meters as well as 10 mm on 300 and 1000 meters; thus the point of impact change is fully parallel. Therefore it’s often unnecessary to have extremely high mounts just to facilitate in-line mounting of a clip-on systems. Various systems allow varying degrees of angular difference. A common maximum angular difference is 2 degrees. If you do want a perfect alignment we do offer the A-700 Clip-On Adapter that will fit onto any of Spuhrs SP-***1 and SP-***2 mounts.
Tilted mounts are necessary when shooting at very long distances. We generally recommend as little tilt as possible as large amounts of tilt really may have a negative impact on the quality of the sight picture. In most cases 6-9 MIL (20-30 MOA) will have no negative impact on picture quality while still providing greater available adjustment range for long-range shooting.
To allow for the greatest available range of adjustment choose a mount with a tilt that is half of the scope’s range of elevation. For example Schmidt & Bender 5-25x56 have a maximum elevation adjustment of 26 MIL (93 MOA,) you should therefore choose a mount with 13 MIL (44.4 MOA) in tilt. Doing so assures that you are able to adjust the sight out to very long distances.
However, when mounted in this extreme elevation it’s common to experience optical phenomena such as an oval pictures when shooting at near targets, etc. We therefore recommend that when fitting a large elevation scope (such as 26 MIL/93 MOA) on a .308 rifle that will only be used out to 1000 meters, to choose a 6 MIL/20 MOA tilt as it’s more than sufficient for that use.
Please note that using a degree of tilt that is more than half of the scope's elevation adjustment will make it impossible to zero the rifle at 100!
Several years ago Spuhr developed our own interface system – the Spuhr Interface – for attaching accessories to a surface. As opposed to many other interface systems on the market the Spuhr Interface can be used not onlyon handguards but also on other products and parts of the firearm – such as their scope mounts – and in their production Spuhr use it for both application.
The Spuhr Interface has outstanding repeatability and durability and it makes installation of accessories such as laser range finders and angle cosine indicators very easy. Installation is done using the same Torx 20 driver as for our rings and clamping screws.
Adding a secondary optic
Though originally more common in the shooting sports, adding a secondary non-magnified red dot sight to work alongside the primary optic can be very useful on long range rifles and on hunting rifles alike as to quickly transition from one target to another without having to adjust the magnification, or to engage targets that suddenly appear close by.
On a heavy rifle that is primarily being shot from a bipod Spuhr recommend placing the secondary optic at the 12-o’clock position using one of our many Picatinny rails or RDS interfaces as it will easier to see over the primary optic than to cant the rifle to the side to use the secondary. On rifles that are primarily fired while standing Spuhr recommend positioning the secondary optic either at the 1:30-position.
Document supply courtesy of Spuhr Mounts.