Up/Downhill corrections

[Shawn Carlock]

I talked with Jeff again today about that and other items. The formula is a complicated mixture of departure angles, trajectory arcs, time of flight and other items. There is also another good point to be made here. While hunting if you want a place to make an error just use some math in the field. I believe the best way to back up the PC is with an Exbal generated angle drop chart printed from the Excell function in the program.

[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. [img]/ubbthreads/images/graemlins/smile.gif[/img]

[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...

[pstimac]

Originally Posted by jwp475

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.