Decreased bullet drop shooting from above or below target?

[7mmstalker]

Forgive me if folks are turned off by my loose standards for distance shooting, a little clarification......
My main concern is that for the next year or so my son will be just starting to shoot with optics, open sights has been his training/ experience area so far. We typically shoot our deer under 100yds.
This is the first season we're making a commitment to find and bag a black bear. His ability to stalk is far behind his shooting skills, this will take time and, I think, trial and error in the field.
Dad doesn't want to track wounded animals, nor accept sloppy hunting ethics.
Eventually he may learn to appreciate better stalking skills, I hope.
A lot of our country is foothills of the north Cascade mountains, some pretty steep.
Still, I doubt there will be the need, or desire, to take a shot a a blackie more than 2-300 yds. max. Just wondering about the trajectory issues on a slope.
Most of the bears I've ever seen were on a hill side.

 

[ShadowsEye]

Really love this guys videos, he's a very good teacher.

http://youtu.be/wTSBcNgGMNo

 

[Centurian22]

Awesome video explanation!!! Thanks!

 

[ShadowsEye]

Awesome video explanation!!! Thanks!

No problem, I really liked all his videos, be sure to check out the others!

 

[MCMXI]

The first example in the video is shooting a target 400 yards away at an angle of -40°. The conclusion is that the horizontal distance is 308 yards therefore we're told to adjust holdover for a shot at 300 yards. What if you're shooting a FGMM 168gr .308 Win load? According to ExBal the bullet will drop 35.6" at 400 yards shooting at an angle of 0°. At 300 yards and the same angle, the bullet will drop 16.0". However, if you input an angle of 40° into ExBal, the bullet will drop 23.8" at 400 yards. So that's almost 8" more drop than predicted using the cosine method.

What about a 1,000 yard shot at a 40° angle? For the same FGMM load the drop at 1,000 yards and 0° angle is 434.9". Using the method described in the video, 1,000 yards x the cosine of 40° is 770 yards and the drop at that range and 0° angle is 212.0". Now input a 1,000 yard shot at an angle of 40° and bullet drop is given as 323.7" which is 111.0" (more than 9 feet!) more drop than indicated using the horizontal distance to target method.

Personally, I'll rely upon software like ExBal and printed data tables to make my adjustments. While I agree with Zak's comment that the horizontal distance to target method is better than nothing, it should be obvious to anyone with access to a basic ballistic program that this method is coarse at best. The video does touch on the vector nature of gravitational force at least ... unlike the AMU's explanation.

 

[MCMXI]

In his second example shooting at a target 500 yards away and at an angle of -60° he tells us to holdover for a target at 250 yards and 0° (cos 60° x 500 yards). According to ExBal and the same FGMM 168gr .308 Win load, the bullet drop at 250 yards and 0° is 9.3". However, the bullet drop at 500 yards and 60° is given as 22.8" which is a difference of 13.5" (more than 1ft).

 

[H&Hhunter]

Claiming that gravity only acts on the bullet over the horizontal distance is inaccurate and misleading, as is claiming that bullet drop is the same shooting uphill or downhill (same +/- angle).

In his second example shooting at a target 500 yards away and at an angle of -60° he tells us to holdover for a target at 250 yards and 0° (cos 60° x 500 yards). According to ExBal and the same FGMM 168gr .308 Win load, the bullet drop at 250 yards and 0° is 9.3". However, the bullet drop at 500 yards and 60° is given as 22.8" which is a difference of 13.5" (more than 1ft).

Of course you are assuming that Exbal is correct. Are you assuming a 100 yard zero, a 200 yard zero? The only way to really prove or disprove any of this is get out with an accurate inclinometer and a range finder on a calm day and actually shoot it off a rock solid rest and record what you come up with.

There simply isn't any arguing with hard science. In a perfect world with no variables such as wind, BC, shooter error, range and angle estimation error, zero for your rifle, the math will be 100% correct.

However add in all the variables that mother nature, firearm mechanics, sight variation, and the human body/mind have to offer and you are correct. It can and will give the appearance that the math is incorrect. Which is a darn good reason to not be long range sky popping at live animals.

 

[MCMXI]

Of course you are assuming that Exbal is correct.

That's a good point and one that made me realize that ExBal uses the G1 drag function without any option to use the G7 drag function. Hornady has a ballistic calculator on their website that does offer both G1 and G7 drag functions.

http://www.hornady.com/ballistics-resource/ballistics-calculator

G1 drag function

Using the "advanced" option in the calculator and the same data provided by ExBal for the FGMM 168gr .308 Win load and the same settings for sight in distance and atmospheric conditions, the bullet drop at 500 yards shooting at an angle of 60° is given as 23.0". The drop at 250 yards and 0° is given as 9.3" so both ExBal and Hornady use the same algorithms for G1 bullets.

G7 drag function

Choosing G7 for the FGMM load gives 17.5" bullet drop at 500 yards and 60° and 8.3" at 250 yards and 0°. So the error using the G7 drag function is reduced to 9.2".

Still, a 13.7" error (G1) or 9.2" error (G7) are both significant if the shooter assumes that there's no error using the "horizontal distance to target" method. The Hornady calculator correctly shows that a bullet drops more at + angles compared to the numerically equivalent - angles e.g. 60° and -60°.