Scope mounts link your airgun to your sighting system but are often overlooked, says Mat Manning
Most airgun shooters put plenty of time and thought into the selection of a new gun or scope, but the significance of choosing the right mounts and ensuring that they are properly fitted is frequently overlooked. Mounts provide the vital link between your airgun and optics, and making the wrong choice will usually compromise accuracy.
It is important to start with a good-quality set of mounts that are right for your airgun and for your telescopic sights. There are plenty of cheap mounts available of course, but, as with most things in life, you tend to get what you pay for — if a deal seems too good to be true it probably is. Reputable brands of quality scope mounts for airgun use include Sportsmatch and Hawke.
If you shoot a recoiling air rifle, your best bet is to opt for a one-piece mount. The additional clamping area provided by this configuration helps to prevent the kick caused by the moving parts of spring-powered and gas-ram air rifles from causing the mounts to creep along the rail, which will result in a loss of zero. Many mounts also have a small pin that can be tapped down into a receiver hole on the scope rail for more anchorage. For airguns with harsh recoil, you can even get one-piece mounts with integral rubberised damper elements, which help to absorb recoil and prevent vibration from shifting or damaging the scope.
Two-piece mounts are the usual choice of airgun shooters who use recoilless pre-charged pneumatics (PCPs).
They are lighter than a one-piece mount and offer more flexibility of movement, which is handy if you need to set them up to straddle a magazine standing proud of the rail. Numerous “special” mounts are also available, including reach-forward designs to achieve correct positioning with very short rails, and models that include an accessory rail into the top half of the ring, which can be handy if you want to fit a compact lamp above your scope. Of course, your mounts also need to match the rail on your gun and the tube of your scope. Most UK airguns feature dovetail-type rails rather than Weaver or Picatinny rails.
The clamps on most mounts will fit 9.5-11.5mm rails — BSA rails tend to be a little wider than the standard, and Sportsmatch produces a mount with an 11-13mm clamp to ensure a good fit and central alignment. Matching the rings of the mounts to your scope tube is straightforward; the tube will be either 1in — often referred to as 25mm — or the larger 30mm.
Choosing mounts that are the correct height is also important, both in terms of achieving good eye alignment with your cheek comfortably positioned on the cheekpiece and for managing the relationship between the line of sight and the barrel. I usually mount my scope relatively low, getting it down as close as possible to the line of bore (providing the arrangement still facilitates a comfortable head position).
Very high mounts exaggerate shift in alignment between the line of sight and the pellet’s flightpath if you cant the gun, which is detrimental to accuracy. That said, you need to have a gap between the objective lens and the cylinder or barrel, and enough clearance to keep the scope tube or saddle clear of the magazine if it’s one that stands proud of the rail.
How to fit scope mounts
With a little care and precision you can fit your own scope mount to your airgun. Take care not to overtighten the screws though, or you will run the risk of crushing the scope tube. Double-check alignments after tightening the screws. Once you’ve finished, you’ll be ready to zero it.
Begin by setting up your airgun on a steady rest and have mounts, screws and Allen keys to hand on a flat, tidy work surface (1). Remove the top sections from the scope rings and place the bases on to the rails (2), ensuring that they are properly seated before tightening them down. When it comes to spacing, I try to allow for 15-20mm between the inside of each mount and the scope saddle, which gives room for adjustment when it comes to fine-tuning eye relief.
If you are mounting up to a recoiling air rifle, ensure that the rear mount, or the back of your one-piece mount, is right up against the recoil plate, if one is present.
Some recoiling airguns also have a hole in the scope rail to accept a pin that drops down from the mount to provide an added degree of anchorage. Place the scope into the mounts, with the saddle fairly central (3). Put the top halves of the rings on and insert the screws very lightly. Try to keep the tension even between all the screws, but keep them slack for now because you’ll need some play to get the eye relief and vertical cross-hair set dead right.
To achieve correct eye relief, shoulder the gun as you would to shoot, and slide the scope backwards and forwards in the mounts (4) until you see a bright, sharp circular image that fills the sight picture. It may help to ask someone to give you a hand with this, but the important thing is to move the scope rather than your head because you should never have to compromise your gun hold to achieve correct eye relief.
It is important to get the gun and the vertical cross-hair exactly aligned to ensure that the trajectory of the pellet rises and falls in correspondence with the reticule. Some shooters use a plumb line to get it dead right, but you can align the vertical cross-hair with anything you know to be dead vertical — perhaps one wall of a house.
With eye relief and vertical alignment sorted, you are ready to tighten down the top sections of the rings. Take your time with this, gently tensioning screws that are diagonally opposite each other to achieve an even loading rather than clamping right down at one end or on one side, which can cause the scope to twist.
Keep working your way around the screws (5), taking them down a little way at a time — don’t overtighten them, or you could crush the scope tube. Holding the short end of the Allen key should prevent you from applying too much pressure — you just need to feel them bite down, there’s no need for any graunching.
Re-check vertical alignment to make sure the scope didn’t twist as you screwed the rings down, which it should not have done, and the job is finished — you’ve got your scope properly mounted. Now you’re ready to zero it on the range (6).