How do you adjust point of aim when shooting uphill or downhill? Will O’Meara says there are numerous factors to consider when shooting at an angle.
Shooting at angle can cause your bullet to strike higher than on level ground. How much it affects your projectile depends on the angle and the distance. In this article we will explore the effects that angle is likely to have on your shot. We will cover a few scenarios to demonstrate the difference, we will look at how to measure the angle and how to calculate the effect it has.
It should also be helpful to look at how angle or steep terrain can force us into different shooting positions and how we can build a solid shooting position for high angle shots. In hunting scenarios, our shot placement will also need to be considered and compensated for.
While the primary purpose of the article is to provide practical solutions, it is worthwhile looking at the theory behind shooting at an angle. The two principles in play here are the law of gravity and the theory of trigonometry.
Let’s first look at gravity. What we need to know about gravity is that it pulls straight down. It doesn’t care if you are on a mountain. Imagine you are shooting from the top of a cliff to a target on the ground; gravity only cares about how far the target is from the base of the cliff.
When trying to wrap my head around this, I think about it in practical terms. Say I am perched on top of a cliff that is 500 metres high. If I shoot straight down, it’s the same as dropping a stone over the edge – I don’t need to make any elevation adjustment, it’s just like the target is at the muzzle of my rifle. Now imagine that there is a cliff opposite me, level with me – aiming here is like shooting on flat ground (let’s ignore the effect of thermals for the moment).
The target on the distant cliff is also 500 metres away, but now I need to apply 3 mRad (30cm clicks) worth of elevation to my scope in order to strike the target.
In this example, both targets are at a range of 500m. The first one is at 90 degrees and experiences 0 metres of gravity; the second target is at 0 degrees and experiences 500 metres’ worth of gravity. Therefore we can imagine that between 0 degrees and 90 degrees, our projectile will suffer varying degrees of gravity depending on the angle. Again, gravity only cares about the distance from the base of the cliff to the target.
Let’s apply our cliff analogy to trigonometry. In a right-angled triangle, the cliff face will be the ‘opposite side’, the line of sight from you to the target will be the ‘hypotenuse’, and the line from the base of the cliff to the target is called the adjacent side. (Does this take you back?)
So, applying our base model of a right-angled triangle, any rangefinder will give us the straight line distance from us to the target (hypotenuse), but what we need to know is the length of the adjacent side, as this is the axis on which gravity operates.
The basic rule of thumb is that the adjacent side is always shorter than the hypotenuse – this is why you would always miss high if you didn’t allow for the angle. It is also the reason that the rule applies the same whether you are shooting uphill or downhill – it’s the same line and experiences the same gravity.
So we can measure the straight-line distance. The only other thing we can measure is the angle. If we have the angle and the hypotenuse (straight-line distance) then we can calculate the adjacent side (shoot-to distance).
There are numerous ways to calculate the angle. The most basic is using an outstretched arm, but this is a bit makeshift so let’s look at tools to give you a more accurate reading. I’ve used a piece of card with angles marked every 10 degrees. Attached to this card is a button on a string – this is rudimentary but it works.
It will give you your angle; you then just need the list of cosines for each angle. You then multiply your straight-line range by the cosine of the angle and the answer is your shoot-to distance, using the table opposite as a reference.
As you can imagine, this could be a pretty tedious calculation in hunting scenarios: “Just wait a moment whilst I check my homemade angle finder, consult my cosine table, find my calculator and make a quick calculation of the shoot-to range…” How can you shorten the process?
You could use a rough rule of thumb (25 degrees = 10 per cent less, 35 degrees = 20 per cent less, 45 degrees = 30 per cent less), but in the heat of the moment such data can be hard to recall – the brain is usually busy enough with windage and elevation data and shot placement.
I have used a cosine angle indicator in the past. This little device is mounted on your scope or action and will show the cosine in a percentage (90 per cent, 75 per cent etc.) You then multiply your straight-line distance by this percentage. So I’m on top of the cliff, I range the target at 600m, my cosine angle indicator says 90 per cent, so my shoot-to range is 90 per cent of 600m = 540m. I apply my elevation or holdover for 540 metres, fire and strike the target.
Again, some calculation is required – and personally I found that I didn’t really want this extra gadget hanging off my scope, since at the time I also had a bubble level on there.
The next tool, and the ultimate solution to my mind, is a rangefinder with built-in angle compensation. I have been using the Leica Geovid HDR for two years now and have it set up so the shoot-to distance comes up automatically. I just range the target and it gives me the shoot-to range, no calculations required.
Let’s look at how, in practical terms, shooting at an angle can affect our shooting position. I favour prone wherever possible; if I’m shooting at an extreme angle, I’m more than likely either falling away from the gun or pushing it down the hill. This can affect how I’m loading the bipod – this was covered at length in the last article.
The point is that you need to focus on building a solid position, and shooting at angle can make that more difficult. In many cases I find that a sitting position can give me a comfortable position for a high angle shot. A long bipod can be a good solution here but a short quad sticks set-up is even better. I also like to use whatever aids are available and will often tuck my bum bag or pack in under my arm, look to support my elbows on my knee, and so on.
It is important to practise these positions and know what works for you and how your kit can be used to its maximum utility. Another important factor to consider is that you will need to apply the windage for your straight line distance – so in theory your elevation could be for 400 and your windage for 500.
The final point I’d like to cover in relation to high-angle shooting is shot placement. When dealing with steep angles, you need to treat the animal in much the same manner as you treat a quartering shot. You need to be aware of where to place the shot to strike the vitals.
This normally means you picture where the bullet will exit. At an angle, this will differ depending on whether the animal is above or below you. If the animal is below you, you should place your shot high in the vitals because it will exit lower and thus maximise the lethality of your shot by hitting both lungs.
The reverse is true if the animal is above you; aim low on the vitals and your bullet will exit high. It’s also worth noting that the taking neck shots at angle can have added complexity – I have seen deflection in extreme cases and as a rule I now avoid neck shots in high angle scenarios.
To give a real-world scenario, let’s have a look at how high angle could affect my own mountain hunting rifle. The calibre is .270 Win, it’s zeroed at 200 yards, and I’m shooting 130gn Federal Vital Shok.
So I’m perched atop a windswept hill on a cold December day. I have a target at 350 yards (line of sight) – the angle is 35 degrees. Without taking the angle into consideration, I will apply 11 clicks (1cm clicks) and miss my point of aim by 16cm (over six inches). If I take the angle into consideration, I will know that my shoot-to distance is 290 yards and I will apply six clicks (1cm clicks).
What if we reduce the range and increase the angle? At 250 yards on a 50-degree slope, my shoot-to distance will be 200 yards. If I fail to compensate, my shot will be three inches high. If my field accuracy is estimated at 1 MOA (meaning I can hit a 1in target at 100 yards, a 2in target at 200 yards…) I could potentially be 5.5in high.
The point here is that if you are hunting in steep terrain, you need to know how to measure and apply your shoot-to range. It can be difficult to practise high-angle shooting owing to the terrain required, but if you know how to use your tools, understand and are well practised in building a solid shooting position and understand shot placement, a tool like a rangefinder with angle compensation will stand you in good stead.