Andy McLachlan takes a look at the various adjustments you need to make when your target is above or below your line of fire
The physical act of shooting either well above or below the ideal horizontal plane can be fraught with many difficulties. Gravity, and its effects on both ourselves and the trajectory of our pellets, works against us even more than it usually does when we are within our comfort zone of nice flat ground, with our target placed in a position that allows the shooter to adopt the comfy ‘butt in the shoulder and head on the cheekpiece’ position we all know and love.
This pleasant scenario allows us as shooters to make the most of both supporting our rifles and ensuring that our heads are positioned centrally to the scope to eliminate that bane of airgun target shooters’ lives: parallax error. When we set up our rifle and scope combinations, we always strive to make sure that our heads are properly positioned so that we are looking straight down the centreline of the optic. This involves the setting up of the correct eye relief and cheekpiece height. The way I check that this has been achieved personally is to close my sighting eye and then rest my noggin on the cheekpiece. If I see a perfect sight picture when I open my eye, voilà!
In an ideal world, where everything we shoot at is positioned to allow for a horizontal shot to be taken, we would all be able to maintain our optimum levels of accuracy. As you know, though, we live in a far-from-perfect world in many ways. Regarding our current perspective of shooting relatively low-velocity, small projectiles at targets that are often very small, this means that any target positioned either above or below, say, 30 degrees from the horizontal can induce many errors into our delivery of a well-placed shot. Thirty degrees is bad enough, but when angles start approaching 45 degrees, things can get very hairy indeed.
There are many reasons for this. The first regards how you intend to support your gun in such a position that will give you the stability to take an accurate shot. When shooting HFT competition, it is almost compulsory for a course-setter to place what is normally a small killzone target high in a tree, sometimes across a valley and often way down in a ditch. Now for anyone who regularly practises yoga or who has been blessed with the ability to move like a snake, positioning yourself – while touching the peg, remember – will not be a problem when you line up for the shot. For the rest of us, this will usually prove to be somewhat more of a challenge.
Depending upon the severity of the incline you face, you then must support the weight of both gun and scope (usually around 11lb) into a position that is not liable to slide or move even slightly as you attempt to take the shot. At a recent round of the UKAHFT series, for example, despite considering myself having a good purchase on the peg with my supporting hand, I watched my scope picture move slightly downwards as I released the shot. My grip had slipped just as I fired the shot, and the pellet landed below my target. This error was due to both the severe angle at which I had the gun positioned and me not double-checking that the position was sufficiently secure before taking the shot.
The next consideration is that you have positioned your head as near as you can to provide the optimum sight picture. If you cannot do this, you may notice a blacking of the image around the outside or even a whiting out of the image as light passes around the outside of the scope’s lenses.
This image distortion will confirm that your scope is not correctly aligned with your eye, leading to our old enemy parallax error creeping in. This manifests itself by your central point of aim appearing to move about in the scope image rather than staying locked onto the target.
As a hunter, you would adjust your parallax focusing at this point to try to remove any error. However, during HFT competition, you are not allowed to make any adjustment to your scope, so must rely upon your ability to make the best of a bad job. Sometimes, when your gun must adopt an attitude approaching 45 degrees or more either up or down, it is very difficult to place your head near its optimum position as you struggle to maintain a steady hold and reduce the wavering about of your gun barrel. In addition to that, it is very difficult – or impossible, sometimes – to position the gun properly in your shoulder.
Finally, you need to consider the flightpath of your pellet as it travels towards its target, reducing in velocity as it goes, and the effect of gravity pulling it down to earth. If you shoot at a horizontal target, the trajectory of your projectile is readily calculated, and can be observed as a gradually increasing curve as it is pulled down by Sir Isaac Newton’s favourite force.
However, as you are not shooting in the horizontal plane when you shoot up into a tree or down into a ditch, the effects of gravity are slightly different. Basically, gravity has less time to influence a pellet’s trajectory, and if you aim using your normal markers you will more than likely hit high of your intended position. To allow for this, we don’t need to have the intelligence of Sir Isaac to work out that if we aim slightly lower than normal for the range, we are more likely to hit the target. This applies both to high and low targets that require a significant angle of rifle to be adopted when preparing for the shot. Like everything in shooting though, the amount of reduction in aim height will depend upon all the other variables such as range and individual pellet performance.
There are a lot of articles online that explain the effects of elevated shooting in far more depth than I have managed here. If you are into that type of thing, you will be able to work things out to the millimetre. For the rest of us, the opportunity of shooting some high and low targets and observing where the fall of shot has landed will give you some idea of how much aim adjustment will be required to hit the target. Basically, when high or low, just aim low!