can someone explain……????????
why, when you sight in on level ground your poi changes when you are shooting up/downhill???? do you aim high or low when shooting down/uphill???
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The reason that you shoot high is very simple.
Your bullet is subjected to gravity for a shorter period when you shoot uphill or down hill as apposed to shooting level
Think about it.
It is very simple,
Roachcreek
1/ If it spent less time in flight, you would shoot low.
2/ The time in flight is actually longer if you shoot to the top of a tree compared to shooting at the base of the tree.
3/ Its due to the effect of gravity and how that effect is reduced when an object is not moving perfectly perpendicular to it.
I watched this thread stumble around the answer before I could post.
The reason that you shoot high is very simple.
Your bullet is subjected to gravity for a shorter period when you shoot uphill or down hill as apposed to shooting level
Think about it.
It is very simple,
Roachcreek
But you are wrong.
up or down hill requires the same adjustment….. must shoot lower
No matter how many times we say this walt.. there are still some who refuse to believe either us, or simply physics.
But you are wrong.
up or down hill requires the same adjustment….. must shoot lower
nice
I know this post is old, but here is a simple “easy to remember” formula to use in the field. As we know you always aim low whether your angle is up or down…
Estimate your range to the target and for a 45 degree angle x’s (times) that distance x .7
For a 30 degree angle x’s the distance x .9
example 50 yard target at a 45 degree angle is: 50 yards x .7= 35 yards. Aim dead on as if you were shooting a target at 35 yards (obviously you have to consider your individual zero…)
That is actually a whole other topic of discussion, but I don’t know how airgunners can hit anything with such large scopes mounted so high above the reciever. The crossover angles become so steep when zeroed at close range that accurate compensation has got to be a nightmare.
If you can, try plugging in a scope height of 1″ and see what that does to the calculation.
Teryx
The discrepancy is not caused by the height that the scope is mounted…
The scope height only magnifies the discrepancy…
There are simple and easy solutions to the compensation issue….
One would be to learn the capabilities of your rifle by shooting it and
recording the number of clicks it takes to compensate for different
yardages.
Another would be Mildots…. You shoot the gun at 10-15-20-25-30yds and
so on and record the mildot location as per the POI for each distance….
And I guess 3rd would be to shoot the gun enough to know instinctively
where to aim. I think they call that Kentucky windage…
All of my scopes have parallax wheels that tell me what the range is within
a foot or 2 and range cards in the scope caps that tell me what mildot to
use, so it is a no brainer to figure out where to aim at any given distance.
I can adjust the line of sight but it isn’t necessary. My scopes are mounted
so that the objective sits 2mm above the shroud and/or barrel. I could go
to a smaller objective scope but they don’t offer side wheel parallax
adjustment… I don’t want to give up the ability to range find with my
scopes.
Here is the Chairgun program with a 1″ scope height…. The discrepancy is
still there. I can change all of the input you would like but the fact remains
that if you are going to shoot at an angle you will have to aim low to hit
the same spot.. The more angle the lower you need to aim…. The more
you point the gun towards the sky or ground, the less the pellet deviates
from the LOS….
If you play with the numbers in chairgun I think you will find that the descrepancy is caused by having a huge scope zeroed at such a close range. You’ve got a line of sight that is 1.996″ above the bore zeroed at 30 yards. Imagine the angle that is creating between the bore and the LOS. Both the primary and secondary crossover will shift considerably at 45 degrees wiith that set-up.
That is actually a whole other topic of discussion, but I don’t know how airgunners can hit anything with such large scopes mounted so high above the reciever. The crossover angles become so steep when zeroed at close range that accurate compensation has got to be a nightmare.
If you can, try plugging in a scope height of 1″ and see what that does to the calculation.
Teryx
This information is as per the Chairgun program…
If your scope is zeroed at 30yds and you put the crosshairs on a target in
a tree at a 45deg angle at 30yds, you will shoot right over it and miss by
.636 inches….Math or no math this is how it works… You have to shoot lower
if your gun is pointed upwards or downwards…. The higher or lower you aim
the more you will have to adjust…. Look at the dotted line. That is the
trajectory at a 45deg incline.. Opinions are great but they are not facts….. If
you want to hit what you are aiming at you have to understand what the
pellet will do, not what you think it will do….
@ 30 yds the POI is 0″
@ 30 with a 45 deg incline it is .636″
Ok, let’s say you are 30 yards from the tree, the squirrel is 40 yards up the tree, your target POA is at 50 yards, so if you use the range from you to the tree then you are going to miss your target. Don’t believe me? Then set up two small targets one at 30 yards and one at 50 yards (both of them straight out in front of you, no angle) and shoot them both with the cross hairs at the center of each target. If you have your scope zeroed at 30 yards your POI might be higher when shooting the 50 yard target but either way if you aim at your target like it’s at 30 yards instead of 50 yards you’ll miss. That’s why I was stating you want to range the actual target and not the distance from you to the tree.
The correct answer is that the distance to the tree is the range that you hold at, regardless how far up the tree the rat is.
I’ll take a stab at explaining it, but without a blackboard it won’t be easy. Assume for a minute that the statement above is true. Obviously, the time of flight changes as the actual distance to the target increases. That is true regardless of whether you are shooting uphill or downhill, so logically you would think that the bullet would drop more in either case. It doesn’t, and the reason is vector mechanics. When the bullet is fired horizontally at a target say 30 yards away, the full force of gravity is acting perpendicular to the flight of the bullet. When the bullet is fired at an angle to the ground (up or down), only a fraction of the force of gravity is acting perpendicular to the flight of the bullet. Remember, gravity only pulls down. The steeper the angle of the shot (up or down), the less actual pull gravity will have perpendicular to it’s flight. The result is that the greater the angle, the flatter the arc of the bullet. In a sense, the effect of gravity on the trajectory becomes less as the angle increases, but this is compensated one to one by the increased time of flight.
So, the steeper the angle of the shot, the flatter the actual trajectory will be, but because the bullet has to fly farther (longer), it actually drops exactly the same amount regardless of the angle.
Another illustration. Take a long flexible pole and hang a weight from the end. If you hold the pole horizontally, the weight (gravity) will pull the pole tip down some amount, and bow the pole. As you raise the pole though (or lower it), you will see that the amount of bow in the pole decreases as the angle gets greater. This is the same effect that gravity has on a bullets trajectory as the angle changes.
Just to illustrate this effect at it’s extreme, what happens when you shoot straight up or down? That is when the angle is at it’s maximum and the effect of gravity perpendicular to it’s flight is zero. At this point, the bullet has zero arc. Of course at this point the range to the target and the time of flight appraoch infinity, so the bullet simply runs out of gas and falls to earth.
All of this is mathematical certainty.
Teryx
Hmmmmmmm, seems like the distance from the ‘tree’ is side a, the distance of the ‘target’ from the ground is side b, therefore the distance from target to shooter is side c, or the hypotenuse. Therefore side c is longer than the distance from shooter to tree. If you use the actual yardage from target to shooter it is farther than from shooter to tree.
I’m not a math expert or shooting expert, but this makes sense. So, range find the target and use that yardage 🙂
Walt, that brings back some uuh, Fun memories! 😥 😆
Mike
If I’m shooting a target in a tree, I range the base of the tree. It works. Having read all the interesting posts, I now know why, whereas before I just trusted it.
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No, the time of flight is less effected by gravity when going up at an angle as opposed to level flight on the surface of the earth.
Draw it ot on a sheet of paper.
It is just to simple to seem correct to you.
I spent 20 years shooting in the mountains everyday where everything was up or down.
Roachcreek