[QUOTE=Michael Eichele;460780]For several reasons that are long and hard to explain, shooting for the actual "horizontal" distance is not the best choice. At closer ranges it works fair. The further the shot and/or the steeper the incline, the more error you will have.
A MUCH better method is to take your bullet drop in either inches, MOA or MILS and multiply by the cosine of the angle. Use that value as a correction. This is called the advanced rifleman method.
The absolute most accurate method is neither but it is a long lengthy proccess to do the math. For most real world hunting situations, the advanced riflemans method is a fairly accurate solution unless you are talking about small varmints.
Advanced riflemans method example:
675 yards, 25 degree slope, bullet drop for 675 yards is 91.75 inches, cosine of 25 degrees is 0.906. Take 91.75 * 0.906 = 83.125"
The reality is though that to do the formula correctly you would find that the actual bullet drop is 80.5" and not 83.125". However, 2.675" off is not too bad for a deer size target when aiming for the lungs.
To shoot for the horizontal range you would be shooting for 611 yards. The bullet drop with my example load at 611 yards is roughly 72". That is roughly a 10" margin of error. A 10" error is too much for a clean shot. The best policy? DONT shoot for the horizontal range.
Thanks for this reply, this is great information!!! So, I assume you run a angle cosine indicator
on your rifle and just do some simple math to correct for angle? Do you find this practical for hunting? I guess if you are making a long shot, you will probably have the time to get everything dialed in and setup.