Angle Compensation

Hi Everyone,

Anyone got any good videos or analogies for explaining the whole angle compensation concept - shooting uphill and downhill vs flat.
I had a couple shots at some tahr last weekend on a pretty steep uphill angle and couldn't for the life of me figure it out.
I've heard the saying, Shoot high aim low, shoot low aim low.
I understand that the bullet will hit lower than expected as the actual distance the bullet is travelling is less, but I don't know how to figure out how much to hold over etc.

Any help is appreciated.

Quick explanation.

Gravity works his best when on a 90degree angle from whatever it's pulling at. So, gravity is at it's most efficient when your bullet is shot horizontally.

When you add an angle (up or down is irrelevant), gravity isn't pulling as efficiently as it can. So you will be shooting higher, at the same distance, than if you were shooting horizontally.

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Originally Posted by sambnz

Hi Everyone,

Anyone got any good videos or analogies for explaining the whole angle compensation concept - shooting uphill and downhill vs flat.
I had a couple shots at some tahr last weekend on a pretty steep uphill angle and couldn't for the life of me figure it out.
I've heard the saying, Shoot high aim low, shoot low aim low.
I understand that the bullet will hit lower than expected as the actual distance the bullet is travelling is less, but I don't know how to figure out how much to hold over etc.

Any help is appreciated.

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And it's not much to do with the distance being travelled being less....actually, that's not really it at all as far as I know. Distance is distance.

The best way I've found to figure it out is by using a ballistic calculator :) flick me a PM with your bullet details and I can give you a little drop chart if you like. Just a quick jam on mine with the .223 (I'll use my 55gr load as it will have the most expanded results, by that I mean it will highlight things much more obviously as it is easily affected) and this is what I've come up with:

Distance; Shot angle; Bullet impact relative to line of sight, in MOA; Bullet impact relative to LOS in Inches
100; 0; 0; 0.01
200; 0; 1.7; 3.51
300; 0; 4.4;13.89

100; 10; 0; 0.04
200; 10; 1.6; 3.37
300; 10; 4.3; 13.55

100; 20; 0.1; 0.13
200; 20; 1.4; 2.96
300; 20; 4.0; 12.52

100; 30 (that's fucking steep); 0.3; 0.28
200; 30; 1.1; 2.29
300; 30; 3.4; 10.83

I hope that makes some sense.

EDIT: the reason I have gone back and added the impact relative to LOS but in inches, is to demonstrate that at those longer distances, you can not accurately hold over time and time again. I purposefully used my little bullets to show an exaggerated example, but I think the point is clear. What is 12.52inches? How high is that? What does that look like at 300 yards? How do you aim an entire sika hind's body width higher? These are the little problems my .223 faces without a scope that dials. Luckily for me - I have a scope I can dial with!

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Originally Posted by Dougie

Quick explanation.

Gravity works his best when on a 90degree angle from whatever it's pulling at. So, gravity is at it's most efficient when your bullet is shot horizontally.

When you add an angle (up or down is irrelevant), gravity isn't pulling as efficiently as it can. So you will be shooting higher, at the same distance, than if you were shooting horizontally.

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Gravity is a constant regardless of angle, it is just acting over a shorter horizontal distance than the LOS distance in an angled shot.

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Originally Posted by Moutere

Gravity is a constant regardless of angle, it is just acting over a shorter horizontal distance than the LOS distance in an angled shot.

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Yeah, what he said :) ^^^

That must be where he got the distance thing from, distance travelled vs horizontal distance.

If you point a range finder uphill though, it says 100yards, then your target is 100yards. However it may be only 50yards of true horizontal travel in which gravity can do its thing on your bullet.

The actual (or true ballistic range 'TBR') is the horizontal distance between you and the target animal. This is the same whether it be uphill or downhill.

Couple of images to help explain TBR:
Attachment 34677

Attachment 34678

Best thing to do (if you haven't already) would be to purchase a rangefinder with built in angle compensation and have it set up to display the actual shooting distance (TBR).

The OP understands the concept, it's the correction they're after.

Edit: sorry jumped the gun there Bryan, a TBR range finder coupled with verified drop chart will be a good start.

As Moutere said, gravity only affects the horizontal component of the projectiles travel. If you are shooting 100m at 45 degrees up or down hill then the horizontal component is cos(45) * 100 = 70.7m, so it has the same drop as a 70m horizontal shot. This is an approximation as the projectile still slows as if it is travelling the 100m plus the extra deceleration of the vertical component of gravity sin(45) * 9.8 ms^-2, but these tend to be negligible over the distances we are dealing with.

Minor point but the method based on horizontal distance gets worse the further out you get. It works fine at "normal" hunting distances out to 400 or 500 or so but after that I would recommend you estimate the angle and put that into you ballistic data.

I would have tried to explain angle shooting as gravity deflection is always the same regardless of angle but with angle some of that deflection is along the line of sight instead of perpendicular to it i.e. vertical. The portion of gravity deflection along the line of sight you don’t see so you are simply left with less vertical deflection. (i.e. what Gadgetman said!)

Couple of other points though about hold over. As Dougie's data shows, a 300m shot with a 30 degree angle (quite steep) changes your point of impact about 3 inches. Typically this would not result in a clean miss on a good central shoulder shot. The other consideration is the angle you are looking at the animal at. If you are above an animal you want to hit it a little high to angle the projectile through the vitals. If you are below an animal you need to aim a little low on the shoulder for the same reason.

Lastly @Dougie, I suggest you sight your 223 in at 200m and re-run those deflection numbers. You will see, with a 200m zero, it is quite easy to hold over on animals out to 300m or so at typical 223 velocities.

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Originally Posted by Moutere

The OP understands the concept, it's the correction they're after.

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Hopefully he still understands it after reading some of the replies ...

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Originally Posted by Gillie

Lastly @Dougie, I suggest you sight your 223 in at 200m and re-run those deflection numbers. You will see, with a 200m zero, it is quite easy to hold over on animals out to 300m or so at typical 223 velocities.

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But I don't like hold-over, that's the point :P

Sorry slightly off topic but one of the reasons I love my .223 so much is that it doesn't lie. It's been a great learning tool for me to have often subtle factors with a big calibre come glaring down at me with the small, light bullet. Wind..doesn't lie. Distance...doesn't lie. I've had great fun learning to dial with my little Weaver scope on this rifle. You'll see the other day when I shot my first deer with it, I dialled! 179 yards, 2.07inches drop, 1.1MOA - I sure did click those four clicks!!! :)

(also at 300yards I have only 448fpe and 1914fps so probably not happily hitting bigger deer out there! I like +500fpe)

http://i.imgur.com/S6sk1nI.jpg

This is listed in metres, but it's perfectly applicable to treat the chart as yards instead.

A note for the keen - As far as I can process, while you reduce your distance for the vertical component, you should still calculate your wind based on the full distance. Particularly of effect the further out/steeper you go.

Has the Coriolis effect been taken into account:P

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Originally Posted by StrikerNZ

A note for the keen - As far as I can process, while you reduce your distance for the vertical component, you should still calculate your wind based on the full distance. Particularly of effect the further out/steeper you go.

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That makes sense now that you mention it, though I hadn't thought about it before - the wind is acting on the bullet over its flight time across the full travelled distance.

Just use a range finder that outputs a horizonatl distance, not slope. Then you can forget all about it.

If you are going to use the cosine method, it is more accurate to multiply the drop of the straight line distance by the cosine. Shawn Carlock has written a good article on this. The most accurate is to get a good ballictic program and input all the data. But the cosine method is close enough out to 600-800 yds depending on your load.

My rangefinder outputs angle so I just input that into applied ballistics along with distance. Its interesting till you start working with angle how much it can affect your point of impact when wanting a clean kill shot in a hunting situ

A recent experience, an uphill shot of 707m called for 4.5 mil but with 10 degree angle factored in became 4.3 mil and a height difference of about 150mm which would in some cases be enough to skim over the back of a fallow or goat.

I wouldnt bother dialling a 223 for 300m shots as gillie says a zero at 200 still doesnt drop significantly in my opinion not to want to hold over a little at 300 considering ow much a 223 drops over 200m , like an inch an average shooter might flinch or pull the shot that much!

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Originally Posted by scoped

I wouldnt bother dialling a 223 for 300m shots as gillie says a zero at 200 still doesnt drop significantly in my opinion not to want to hold over a little at 300 considering ow much a 223 drops over 200m , like an inch an average shooter might flinch or pull the shot that much!

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I'm not an average shooter. :)