Aim Above or Below?
10-30-2010, 08:49 AM
#1
Spike
Thread Starter
Join Date: Oct 2010
Posts: 8
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?
Please check out my facebook page and fan page. We are a local magazine aiming to preserve traditional hunting and the values it has wrought in America and would love your input. Thanks!
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?
Please check out my facebook page and fan page. We are a local magazine aiming to preserve traditional hunting and the values it has wrought in America and would love your input. Thanks!
10-31-2010, 06:41 PM
#3
Fork Horn
Join Date: Oct 2009
Location: NC
Posts: 113
QUOTE: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?
Because he is a lousy hunter, with a cheap scope.
He'll spend the next day in the gunstore, bitching about how his
"x-mag" is a worthless gun.
Because he is a lousy hunter, with a cheap scope.
He'll spend the next day in the gunstore, bitching about how his
"x-mag" is a worthless gun.
11-03-2010, 07:23 PM
#4
Fork Horn
Join Date: Jul 2010
Posts: 131
that is the most complicated explanation for shooting uphill and down I have ever tried to read. The reason most people miss is because of misjudged distance. if a deer is down hill at 400 yards that dont mean you aim at 400. Leave him at the same distance but bring him straight up to your eye level and thats the distance you aim. He may be 400 yards down hill but actually only be a hundred yards out. shoot for what he would be if you brought him up to eye level.
11-04-2010, 10:13 AM
#5
Nontypical Buck
Join Date: Dec 2006
Location: Lubbock, Texas
Posts: 1,401
On a 200 yard shot on a flat shooting rifle the difference is only going to be an inch or so even at a 30 degree angle which is a pretty extreme angle. (It calculates out at being a 175 yard shot instead of a 200 yard shot).
On a 400 yard shot at a 30 degree angle it is going to start making some difference as that would be the equivalent of a 350 yard shot on level ground. Maybe 5 or 6 inches on a flat shooting rifle. Again, a 30 degree angle would feel like you are almost shooting straight down and having a good angle through the vitals would be as important as anything on a shot at that extreme angle.
