How to set up scopes and scope mounts to get the best accuracy
- Credit: Archant
Gary Chillingworth brings us some vital information for accuracy
Recently, I was lucky enough to test the Optisan MTC EVX 10 x 44, a great scope with wonderful clarity and depth of field. Then shortly after that, I was asked how to set up a scope and get the best from it, so I thought it would be a good idea to look at some scope mounts and how to set up a telescopic sight for HFT and hunting.
If you want a good all-round telescopic sight for a sub 12ft.lbs. air rifle, then a scope with an objective lens between 32mm and 44mm is a good place to start. Magnification should be 10x or under, and an adjustable parallax can be an advantage, especially if your eyesight is not 20/20. Some scopes to look at are the MTC Range, Viper, Connect, EVX and Mamba, or the Tac30, Panorama and Varmint from Hawke. All of these are great first scopes and won’t break the bank.
The first thing to look at is mounts. They come in two main heights (medium and high) and two main widths (25mm and 30mm) to accommodate different tube sizes. Then you have single or double strap, and single or double screw, but unless you are going to spend a fortune on single-strap, single-screw Leupold mounts, then stick with double screw single, or double-strap mounts, from either BKL or Sportsmatch. The double-screw mount gives both rigidity and stability and it will hold your scope securely onto your rifle.
So which height do you buy? Well, most hunters and HFT shooters try to get the scope as close to the barrel as possible. This practice will give a shallow pellet trajectory, a real boon as it means you will only need one aim point to cover a large distance.
Some shooters like to use a high mount and this type of set-up helps to close up the trajectory at 40 yards-plus, but having the scope set high can cause issues with rifle canting (leaning over left or right) and it makes the closer targets much harder to hit.
When you attach the mounts, make sure the securing bolts all point the same way - this is usually to your right as you look through your scope - and try to make sure they are as far apart as possible. This will create a more stable platform for your scope than having the mounts close together. Think of holding a long stick. If you hold it at both ends, it’s stable; if you hold it at the bottom, it can wave about.
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Eye relief and set-up
After you have attached the base of your mounts to your rifle’s scope rail, place your rifle into a rifle stand or, if you have one, a Black and Decker Workmate. Then place a spirit level on the scope rail and adjust until the rifle’s dovetail is perfectly level and stable. Place the telescopic sight in the mounts, put the top of the mounts on and finger-tighten the screws. Make sure your scope is set to 9 or 10 magnification and if your scope has parallax adjustment, set it to about 25 yards.
You will now need to set up a plumb line with a nice heavy weight and a thick piece of rope, and place it 20 yards in front of your unloaded rifle. Look through the scope at the plumb line. You might need to adjust the fast-focus ring at the ocular end of the scope - the ocular lens is the one nearest your eye.
Wind it in and out by rotating the ring clockwise and anti-clockwise respectively, until the plumb line comes into sharp focus. Look through the scope and make sure the vertical crosshair is lined up perfectly with the plumb line. When it is, tighten up the screws so that they hold the scope securely, but be careful not to overtighten. A good rule of thumb is to tighten the screws enough to hold the scope so that it is just beyond finger-tight and then give another eighth of a turn.
You can then remove the rifle from the rest and take a prone position with the rifle in your shoulder. Loosen the bolts holding the mounts to the dovetail, and slide the scope back and forward along the rail. You will see that when the scope is close to your eye, a thick black ring will appear around the edges of the sight picture. Push the scope forward until this ring disappears so you now have the scope at the optimum distance from your eye. This is the scope’s eye relief.
You can now tighten up the mounts and as long as you don’t loosen the bolts holding the scope in the mounts, you should be able to remove the scope from the dovetail to clean or adjust the rifle and when you put it back on, you should not have to re-zero the rifle, although a check of zero before hunting or target shooting is always a worthwhile thing to do.
You now need to set the parallax. Parallax error (PX) is one of the biggest reasons for missed targets and injured quarry in rifle shooting. To quote my old Beginners to Winners series: ‘Hold your hand out in front of you and raise your index finger so it is pointing towards the ceiling. Close one eye and, with your arm outstretched, move your hand so that your finger covers a point on the wall. Your finger is your scope’s reticle and the point that it is covering up is the target.
‘Now, move your head left and you will see that even though your finger has not moved, when your head is to the left, your finger/reticle is now to the right of the target. So, now move your finger back to the left so that it is covering up the target again and move your head back to its central position and your finger should now be to the left of the target.’
To compensate for this, most quality scopes have parallax adjusters, which will enable you to set your scope with a parallax of 40 yards for a 40-yard target or 10 yards for a 10-yard target, so no matter how much you move your head about, your crosshairs should remain on the target and it will be nice and sharp.
The problems start when you want to shoot HFT, or you don’t want to be resetting the PX on your scope. If you are hunting, you don’t want to be moving around adjusting scopes. So, it is best to find a setting that is a good compromise and this way, the PX setting on a scope can be left alone.
To set the PX on a rifle, find a shooting range or a place to shoot - this must be land that you have permission to shoot on - and then with a tape measure set up some targets from 10 to 45 yards with targets every 5 yards. Old cardboard boxes are perfect. Fill them with dirt or sand and make sure there is an adequate back stop to catch any stray pellets.
Look through your scope at the box 45 yards away and set your magnification to 10, then wind the parallax adjuster back to about 13 yards. If you check the target at 45 yards, you will see that it is extremely blurry.
Gradually, wind the parallax adjuster forward and you will notice that the box will slowly come into focus. As the image becomes sharp and clear, stop. There is a good chance your PX setting will be between 25 and 30 yards. Look through the scope and you will see that the targets from about 17 yards to 45 will be clear - depending on the scope - and from 8 to 16 there will be varying amounts of blur. If you are only ever going to shoot to 20 yards or thereabouts, wind the PX wheel back until the 8-yard targets come into focus.
If you are going to shoot competitively, though, you can use blur to rangefind. Take a look at the 45-yard target and wind the PX adjuster back toward the 20-yard mark and you will see the 45-yard target just starts to blur. When it does this, stop, and take a quick look at the 35-yard and 40-yard targets, which will still be clear. By doing this, if you ever look at a long-range target and see some blur, you will know it’s over 40 yards.
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