Up/Downhill corrections

[Aragorn50]

Any thought to the significance of an angled scope base? I have a 45 MOA base on my "50", which amounts to 0.75 degrees. Scope base and barrel are therefore not parallel.....
Factor of least significance? Gosh I love this stuff..

Scott

 

[Gustavo]

[ QUOTE ]
Any thought to the significance of an angled scope base? I have a 45 MOA base on my "50", which amounts to 0.75 degrees. Scope base and barrel are therefore not parallel.....
Factor of least significance? Gosh I love this stuff..

Scott

[/ QUOTE ]

Scott,

That angle is of almost no consequence. Take into account that the LOS and the LOF are never paralell.

Once you have characterized the trajectory ( Zero Range, MV, BC, DC and environment conditions ) then you have all what is needed. Assuming you have zeroed it at level-fire situation.

Drop is always measured in a vertical direction regardless of the elevation angle of the trajectory. In other words it does not consider the sights or zero. No matter also if it is measured along either a level range or a slant range, since Drop is a vertical distance as it's measured between the extended bore line ( Line of Fire ) and the point where the bullet passes.

 

[blackco]

OK. My dad always told me there was a difference between shooting uphill and shooting downhill and after reading what the pros had to say I always told him BS. (politely, he raised me that way)

Now maybe I'm taking this to an extreme but I'm a very visual person; I just printed out a random trajectory graph (this one only goes to 400yds)...if I rotate it clockwise ABOUT 45* the bullets in this chart "SHOULD" be dropping straight down (no further effect from gravity) and if I rotate it the same angle counterclockwise...the bullets in this chart are just starting to fall below horizontal (full effect of gravity).

So, a few questions arise in my little pea brain:
A. Is this what you guys are already talking about and I'm just starting to catch up?
B. Is this to extreme to matter to us as shooters?
C. Am I just oversimplifying a very complex process because my brain is having trouble grasping the whole thing?

If you print out a drop graph and rotate it you will see what I'm talking about. I understand the horizontal distances are affected by rotating the graph but the effect is still there. I have a feeling there is probably a very easy explanition for what I am seeing, I just don't know what it is. /ubbthreads/images/graemlins/smile.gif

 

[pretex]

is this correct to use then:


Uphill 800 x .94 = 752

Downhill 800 / .94 = 851

 

[jwp475]

As long as the angle up or downhill is the same then the correction is the same...

 

[WildcatB]

As long as the angle up or downhill is the same then the correction is the same...

Not true at longer distances. At longer distances + or - effect of gravity on the bullet is seen.

Here's an example as per JBM:

Bullet/BC/MV/Elevation/Temp/Target/Distance/Angle/Drop
7mm /.87/3250/5000/59/2000/+45 714.2"


Bullet/BC/MV/Elevation/Temp/Target/Distance/Angle/Drop
7mm/.87/3250/5000/59/2000/-45 677.2"

The difference being 36.9 inches. The time of flight is a little different too.

 

[jwp475]

If you are correct then why doesn't Exball ask if the angle is uphill or downhill?

I don't know what you used for a zero distance, but with a 100 yard zero Exbal shows a correstion of 685.3 inches and there is no way to imput a + or - degree it simply asks for the degree, I am going with Exbal as its accuracy is proven IMHO

 

[MagMan]

+1 jwp

you sure would think that a program that has a humidity input would know there was a difference between + & - angles.

I may be wrong but I think someone is confusing their markup with margin.

Maybe we can get Ward to put little -'s on the ACI's.

 

[Shawn Carlock]

The angle is all that matters from horizonal, it does not matter if it is up or down just that it is. A given 45 degree shot uphill is the same dope as the same shot but 45 degrees downhill.

 

[Buffalobob]

OK. My dad always told me there was a difference between shooting uphill and shooting downhill and after reading what the pros had to say I always told him BS. (politely, he raised me that way)

Blackco

Father's Day is coming up. You should save up your allowance and get him something nice for having a lot of patience with you.

 

[jwp475]

The angle is all that matters from horizonal, it does not matter if it is up or down just that it is. A given 45 degree shot uphill is the same dope as the same shot but 45 degrees downhill.

There you have it......Makes no difference up or down it's only the angle that matters....

 

[Buffalobob]

Gravity only works in one direction. It is always down.
A bullet that travels uphill is working against gravity and is being decelerated.
A bullet that is going downhill is working with gravity and is being accelerated.

 

[jwp475]

Gravity only works in one direction. It is always down.
A bullet that travels uphill is working against gravity and is being decelerated.
A bullet that is going downhill is working with gravity and is being accelerated.

Are you saying that you believe that the correction will be different shooting downhill VS uphill?

 

[WildcatB]

If you are correct then why doesn't Exball ask if the angle is uphill or downhill?
IMHO

I don't know. I don't use Exbal, but maybe there's a way you can enter up or down angles? Or maybe Exbal left something out???

I am going with Exbal as its accuracy is proven IMHO

I was just trying to help out. Stick you head in the sand if you want but here's the link, try it for yourself. http://www.eskimo.com/~jbm/calculations/traj/traj.html


SHOOTING UP: Gravity is working against the direction of the bullet when it's shot upward. This slows it down slightly and effects the trajectory which changes the point of impact lower relative to the drop using the same angle shooting down. The change is so slight that you don't really see a significant difference until your target is very far away - beyond a 1000 yards for most loads.

SHOOTING DOWN: Gravity is working in the same direction as the bullet when it's shot. This speeds it up slightly and effects the trajectory which changes the point of impact higher relative to the drop using the same angle shooting down.

It's Physics. I didn't make this up. You don't really see the effect until after 1000 yards. Make sure you change the range to 2000 yards otherwise the difference will only be a inch or two at a 1000 yards. If you want to see the effect even more, change the range to 3000 yards.

jwp475 and MagMan I tried to use small words, but if all this is too much for you to wrap your heads around then just continue to ignore physics and take Exbal's apparent lack of angle direction input as gospel proof that what I'm saying is wrong. I wouldn't want you to actually have to think about something.