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Aim Above or Below?

A controversial issue

If the target is not at the same level as the shooter, should he aim the rifle above or below the critical point?

As you can see in our (exaggerated) graphics, when you aim horizontally using a properly calibrated scope, the barrel of the rifle tilts slightly upwards to compensate for the parabolic effect.  In other words, the bullet crosses the sight line immediately after you pull the trigger and travels above that line most of the time. 

If you follow our sight-in adjustment guidelines, as described in another article, both lines will intersect at the vital zone at about 250 to 300 yards. For a target located about 100 yards, the bullet will hit 3 inches above the crosshairs’ center.    

However, what happens when you are lying on the top of a hill and the game moves in the valley below? What if it is you in the valley and a sovereign reindeer roams a mound?

Here is a typical story: 

A hunter, standing at the foot of a hill sees a white-tailed doe on the top. He focuses slightly behind the shoulder bone of the deer, fires and…  The female deer flees as the bullet raises dust behind her. Missed miserably. But, why?

To understand the reason we must consider which factors affect the trajectory of a bullet. These are:

• Thrust

• Rotation

• Nutation (pitch)

• Air resistance

• Gravity 

• Mass

• Shape of the bullet

• Initial velocity

• Length

(Actually, there are only two important factors: the ballistic coefficient of the bullet and its velocity.)

Modify one of these factors and the outcome will vary as well. For instance, if you adjust the scope for a cartridge that leaves the muzzle at 1063 yards per second and then use another cartridge that develops an initial velocity of 890 yards per second, the impact at 250 yards will hit about 4 inches below.

Normally, when we sight-in a rifle both target and barrel are more or less at the same level. 

However, when shooting upwards, we are modifying several factors at once: gravity and air friction, among others. A bullet fired upwards tends to slow down due to gravity. Conversely, if fired downwards, it tends to accelerate.

To counteract the effect, always aim below the desired point when shooting upwards or downwards

In real life, the effect becomes important when the angle between the target, gun and the horizontal line across the muzzle exceeds 30 degrees. 

Now, by way of entertainment, consider this ballistic question:

If you fire horizontally and drop another bullet with similar characteristics from the same height, which one reaches the ground first?  

CVC
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Not sure this is

Not sure this is controversial.  It is a pretty simple concept, gravity only affects a bullet over the horizontal distance which is why whether aiming up or down you have to shoot lower than the range finder reading unless it can correct for the elevation.

Often when I am in a tree, I take a reading at a tree straight across from me and down at the base.  Usually not much difference, but it is always closer straight across.

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Yeah, That ^

I agree that's it not controversial, only often misunderstood.

Conventional wisdom would say to aim high if it's uphill and low if it's downhill.

But physics shows what CVC said, gravity only affects the bullet over the horizontal distance, not the hypotenuse of the triangle created by shooting uphill or downhill.

The answer to the last question is both will reach the ground at the same time. Gravity affects both bullets exactly the same whether they are propelled straight out or dropped straight down.

Kinda neat, ain't it?

 

CVC
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The last question will hurt

The last question will hurt one's brain if they think about it too much.  It is kind of like dropping a feather and piece of lead - they will fall at the same rate, but only in a vacuum.  I wonder if that part is the same about the bullet too?  I wonder if air density and other factors would prevent the bullets from falling at the same rate.  Same about the propulsion - would it affect the rate of drop?

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At most hunting ranges if you

At most hunting ranges if you have your rifle zeroed 2-3 inches high at 100 yards just hold like you normally would and take the shot. If its farther and you miss you'll generally have time for a follow up shot to adjust.

 

Dont over think it, just put the cross hairs behind the shoulder and squeeze.

CVC
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It really depends on the

It really depends on the angle if you have to be concerned about it.  I shot my mountain goat at a ranged distance of 271 yards, but I aimed as if it were 225 yards.  It was a steep steep 70 degree uphill shot so if I had just put it on the shoulder I would have missed or just wounded the goat.  Instead i pancaked him so it does matter even at fairly close distances depending on the steepness of the terrain.

And how did I determine the 225 yards?  Just some informal calculations which means that I pretty much just guessed, but hey, I like to think it was an educated guess.

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It also depends on how you

It also depends on how you sight in your rifle. For however you sight your rifle, the difference between 271 and 225 yards must be able to cause a miss. For me I am still holding dead on the animal at both ranges. At 225 my bullet is almost back to point of aim and at 271 it is a bit low. For me, and my 270 it wouldn't have made a difference at that range. But if it was sighted differently than it could have made a big difference. For my sighting, I have to get out to 350 yards or beyond before it really starts making a difference.

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My rifle is sighted in at a

My rifle is sighted in at a 200 yard zero.  I use a Boone and Crockett reticle that has hold over points.  The crosshair is 200 and then there are lines for 300, 400 and 500.  If I was aiming for a true 271 yards, I probably would have held the 300 yard line a little low or even right on center of the animal.  Since I calculated the distance to be 225 I just held the 200 a hair above center.  It worked out as it just took one shot to bring the goat down and it hit almost where I was aiming.  I think wind drift affected it a little or I pulled it a little, but who knows. 

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Oh and CVC... are you sure

Oh and CVC... are you sure that you were shooting at a 70 degree angle. Don't get me wrong, sheep and goat habitat is severely steep (and I know sheep and goat habitat) and angled shots are the norm. But it is hard to even have a shot opportunity that is at 70 degrees. It would be very hard to find a situation where at 271 yards you would be able to see an animal that was 70 degrees above you because the ground it would be standing on one many times be blocking your view. A 45 degree slope is insanely steep. Use your arm to simulate that and think of a hill that was at that angle. You are not able to stand on a 70 degree slope.

It is also very hard for untrained people to judge slope when they are standing on it because of your perspective. It took me a while to be able to accurately estimate slope with my bare eyes for all the forms I had to fill out for my internship. Luckily we had clinometers to accurately measure it.

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Nah, not sure about the

Nah, not sure about the actual incline.  I don't think it was 45 degrees though.  It was so steep that I could not stay in a prone position in one spot.  I would dig in and even found a hole to put my elbow in and would almost instantly start to slide down hill.  Also, it was so steep that it took a half hour to climb 200 yards.

I just did some calculations and the difference from the ranged distance of 271 yards at a 70 degree angle (if that is what really was) and the actual horizontal distance is and it came to 254 yards.  So my in field calculations were wrong.  I think it might be a good idea to calculate some distances before going to hunt in steep terirtory to get a sense of how to compensate.  Oh well hind sight is 20-20.

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Hey, you put a 9 and a half

Hey, you put a 9 and a half inch billy on the ground, on the side of a treacherous mountain in a far away land. I would not really say that your calculation was "wrong". You were aware that would have some sort of effect on your shot and you made a modest adjustment to your aiming point and you hit your goat. That doesn't seem "wrong" in my opinion. You describing your shot just got my blood pumping. You are so lucky... WHY CAN'T I DRAW A TAG?!

Congratulations again on that goat man... I am so jealous!