2 Cool Fishing Forum banner
1 - 9 of 9 Posts

·
Wingnut
Joined
·
60 Posts
Discussion Starter · #1 ·
Ok, I can sight my rifle in on the bench on flat ground at say, 100 yards. I then can climb into a stand at say, 10 ft., and at 100 yards my rifle is shooting quite a bit higher from the elevated stand. Same distance same gun two different points of impact. I figure it has to do with line of sight or even the scope heigth you were discussing previously. I have tried this time and again even when shooting downhill off a mountain and it DOES shoot higher. Ya'lls thoughts???
 

·
I'll keep my gun...You keep the change
Joined
·
10,507 Posts
The hoary old question of where to aim when shooting up or down hill regularly rears its head. It seems that many hunters understand that shooting at a steep angle changes the point of impact, but can't remember why or in which direction.
The correct answer is to hold lower than normal when shooting steeply up or down hill at long range. (At gentle angles you can ignore the problem altogether over the maximum point blank ranges of hunting rifle cartridges.)
This seems odd to many, and they insist on making the problem more difficult than it needs to be. But the reason is simple. Trajectory, the bullet's flight path, depends on the horizontal (level) range to the plane of the target, not the line of sight range up or down hill. Your eye sees the line of sight (slant) range from your position to the target, which is longer than the horizontal range.
Remember that it is gravity working on the bullet during its flight time that causes it to drop. If you were to shoot straight down, say from a tethered balloon, the bullet would have no curved trajectory, it would travel toward the earth in a straight line, just as if you simply dropped it. Likewise, if you shoot straight up, the bullet travels up in a straight line until its momentum is expended. Again, there is no curved trajectory.
You can infer from this that the farther from the level position a rifle is held when a bullet is fired, the less the bullet's drop will be over any given line of sight distance, whether it is fired up or down. Since your sights are set to compensate for bullet drop, and there is less bullet drop when shooting at an up or down angle, you must hold lower than normal to maintain the desired point of impact. For example, if you are shooting up or down at a 40 degree angle and the line of sight range is 400 yards to the target, the horizontal range is only 335 yards. 335 yards is the distance for which you must hold.

TS......hope this helps
 

·
The Jammer
Joined
·
3,594 Posts
Troutslayer (we meet again) was posting his post above as I was writing mine, and I had not seen his prior to posting mine, but he is right on. Following is what I was writing as his was being posted.

I gotta tell you that for most hunting situations, the angle up or down is a non event. Anyone who has played around with one of the ballistics programs (one that takes into account everything, including angle up or down), will tell you unless you're talking angles of 30 degrees or more on pretty long shots 300+, that the difference is negligible.

I would say your problem relates more to steadiness of your rest, and other external variables.
Your scope height will be the same whether you're shooting from the ground or from an elevated stand. So don't worry about that.

Here's some data: for a .450 bc 168 gr .308 bullet at a muzzle velocity of 2600 fps which is zeroed at 200 yards.

Shooting a target at 300 yards requires 6 clicks (1.5 moa) up on a 1/4 moa/click scope with zero up or down angle to the target.

With a 20 degree up or down angle the correction is 4 clicks up on a 1/4 moa/click scope.

Two click difference equals 1/2 moa. .5" at 100 yards, 1" at 200 yards, and 1.5" at 300 yards-- Negligible. and 20 degrees is more than most hunters in Texas will ever encounter.

At a 30 degree angle the difference is 5 clicks or 1.25 moa. Now that's almost 4" at 300 yards, so now it's starting to get significant.

But again 30 degrees is really steep. That's sheep hunting kind of stuff.

Remember your high school geometry. That if the angle of that right triangle is low, the difference in the length of the base and the hypotenuse is insignificant. As that angle increases, the difference between the length of those two lines gets greater. The hypotenuse being the measured distance to the target, while the base of that triangle is the distance over which gravity acts on your bullet.

So it looks like you have a different problem.

When you say "my rifle shoots quite a bit higher from the elevated stand." What is quite a bit? How much??

THE JAMMER.
 

·
I'll keep my gun...You keep the change
Joined
·
10,507 Posts
I cant find any photos or illustrations on the net......but if you know a little about trig.........the hypotenuse is always the long side of an Isosceles triangle.....which if you were shooting uphill or downhill at 30 degrees and were 300 yds away ...

The cosine of 30 degrees is 0.87. The horizontal range for the bullet is only 261 yards (300 * 0.87). In order to hit the target we should hold the gun as if the target were only 261 yards away not 300 yards. If we shoot where the scope crosshairs intersect the target we will shoot over the target. In the field, you probably don't really know the slant range or the slant angle very accurately. Just remember to always aim lower, because any slant range shot, either downhill or uphill, will be higher than if it were a horizontal shot.

 

·
The Jammer
Joined
·
3,594 Posts
That's why my Leupold rangefinder not only gives me slant range to the target, but it also gives my angle, and horizontal distance to my target. In your example above it would show range 300, horizontal range 261, angle up or down 30 degrees. I just look at that horizontal range and take my shot accordingly.

And yes if you have the time and the animal is undisturbed, I would look at my program (which is in a watch like device I wear on my wrist), and crank in the correction. If I don't have the time, I should have known my ballistics for that gun well enough that I could shoot on the fly, and probably hit that 10-12" heart lung shot.

Also when talking about change in hold for angled shots, we are talking about a right triangle, in which again, the hypotenuse is still the longest of the three legs.

Also troutslayer your statement "if we shoot where the scope crosshairs intersect the target we will shoot over the target." The validity of that statement is totally dependent upon where you have the rifle zeroed. If the rifle is zeroed for 261 yards (which is pretty close to where you would be if you were sighted in about 2.5-3" high at 100 on most guns/loads), and you put the crosshairs on the target on that 300 yard 30 degree down angle, you WILL hit the target. If you're zeroed for 261 yards you will hit that target whether it's 30 degrees up at 300 yards, 30 degrees down at 300 yards, or level at 261 yards.

I think a more accurate statement might have been if you shoot at that target that is 300 yards away, and at a 30 degree down angle, and you shoot at it as though it were 300 yards away, you will miss it it every time.

And again I not sure I can totally agree with your last sentence which says "always aim lower." Key word being always. Yes the bullet will hit higher, but on short shots and small angles up or down, the difference is so negligible that I don't think we want to over analyze. K.I.S.S.

This again is a perfect illustration of how valuable having a software program is. I can't tell you how many times I've sat around my den with mine and played "what if" for hours at a time. Changing different parameters to see what the net effect is. some things have a measurable effect. Others do not. I feel that knowing as much of this kind of info as possible enables me, in the field, to be able to more accurately make that "decision on the fly" when I don't have time and be as accurate as I possibly can.

THE "MAN WE'VE HAD SOME GOOD ONES THIS WEEK" JAMMER
 
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top