Scope mounts provide a vital link between your air rifle and your aiming system – most often a telescopic sight (often referred to as a scope) – and cutting corners in this area can be detrimental to accuracy. Get it right, and your riflescope will be securely connected without risk of it being shifted by recoil of the occasional accidental bump.
Before rushing to fit a new scope to your air rifle, the first important thing to ensure is that you have the right mounts. Going for a cheap option will almost always turn out to be a false economy, so opt for a quality brand. They may cost a little more but they will last way longer and give a far higher level of performance. My first choice for most of my scope-mounting is the Sportsmatch brand – made in Great Britain to very fine tolerances, these high-quality mounts are extremely reliable.
The clamping part of your scope mounts need to match the scope rail on your airgun. This will usually be dovetail or Picatinny but check before you buy and confirm the exact specifications as there can be variation between dovetail rail widths on different brands of rifle.
The ring part of your mounts will need to match the diameter of the tube of your chosen scope. This will most often be one-inch or 30mm but be sure to check as larger scope tubes are becoming increasingly popular.
Your mounts also need to be the right height. I like to mount my scopes as low as possible – usually with around 1mm to 5mm clearance between the objective (front) lens and the gun. It is often necessary to go higher to ensure that your scope clears the magazine if you have a multi-shot airgun with two rail sections that span the mag’.
Standard two-piece mounts are suitable for most pre-charged (or PCP) airguns, although it can be wise to opt for the extra clamping power of a one-piece mount to prevent creep caused by the recoil of a spring-powered or gas-ram airgun. You may even need to fix an arrester block to the rails behind the rear mount to prevent creep if your airgun has particularly harsh recoil. If you’re in any doubt, tell your local gun shop what airgun/scope combination you intend to marry together, and they should be able to help you make the right choice.
When you’re ready to fit everything together, set yourself up on a clean workspace (a clean workbench or kitchen table is perfect) with all the kit you’re likely to need close to hand. The gun, scope and mounts are pretty obvious but there are a few other handy extras that will help you to do the job properly. Always ensure that you have the correct Allen keys to fit the screws on your scope mounts – a poor fit will result in mangled screw-heads so don’t compromise. And, to ensure that the vertical alignment of your crosshairs is perfect, a level will also be useful. Many gun shops sell specialists bubble levels that fit to scope rails, but you can achieve the same result for just a couple of pounds with a replacement bubble module from your local hardware or DIY store.
Take your scope mounts and begin by removing the screws that fasten the top half of the circular cradle that will hold the scope tube. Lift off the tops from both mounts and put them somewhere safe along with the screws. Then loosen the screws that hold the base clamp of each mount until it opens wide enough to fit to the rails on your airgun. With the mounts in place, loosely tighten the screws so the mounts can still slide along the rails – this applies only to dovetail rails as they won’t slide on a Picatinny rail.
Before you place the scope into the mounts, adjust its reticle focus to suit your eye. This adjustment is done by twisting the ring by the ocular (rear) lens. Place a blank sheet of paper on the table, loosen off the locking collar on the ocular focus adjustment ring, stand up and peer through the scope in the direction of the paper. With the blank background of the paper filling the sight picture, there’s nothing to distract your eye from the crosshairs so you can simply adjust the focusing ring until the reticule looks as bold and crisp as possible. Tighten the locking collar and the task of focusing is complete. If you’re working indoors, a white wall will serve the same purpose as the sheet of paper.
The scope can now be placed into the mounts, which should sit approximately 20mm either side of the saddle beneath the windage and elevation turrets towards the middle of the scope cylinder. Arrange the scope so the elevation (up and down) turret is at the top and the windage (left and right) turret is on the right as you look down the scope from behind. You can now place the top halves of the rings back on. Tighten the screws, but only loosely so the scope can be turned within the mounts.
The next task is to ensure correct eye relief – the required distance between your eye and ocular lens to achieve the optimum sight picture. To do this, mount the gun into your shoulder (very carefully because the scope is not securely attached) and then look through the scope with your head in the usual place on the cheekpiece. Don’t adjust your hold or the position of your head but instead slide the scope and mounts either backwards or forwards on the rails until you achieve a clear, bright sight picture that fills the tube as you look down the scope. When you’re satisfied that eye relief is exactly right, place the gun back in the support and fully tighten the base of the mounts to the rails of the gun. For Picatinny mounts, which won’t slide, you will need to lift them off to change their position.
Now it’s time to get things dead level. Using either a proper shooter’s bubble level or a DIY bubble balanced on the scope rail behind the rear mount, make sure that your gun is set absolutely horizontal in its rest. Look using either a vertical plumb line or a wall edge or doorframe that you know to be perfectly vertical, look through the sights at the plumb line and twist the scope (without shifting the angle of the gun) until the vertical crosshair is aligned with the vertical line. This will ensure that, wind and canting aside, the rise and fall of the pellet’s trajectory will always correspond with your vertical crosshair.
Eye relief and scope angle are now correct, so you can now tighten the top clamps of the scope rings, and there is a way to do this properly. By first gently tightening the rear left screw on the rear mount and then gently tightening the corresponding rear right screw on the front mount, you can gradually achieve an even pressure that won’t twist the scope. Continue working around the mounts, tightening those corresponding “opposite” screws until you feel the grip is sufficient to prevent your telescopic sight from creeping. You want them to just start to bite, but not too much as there is a risk of them crushing the scope tube.
Your scope is now correctly mounted and ready for zeroing.
