Decreased bullet drop shooting from above or below target?


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7mmstalker
August 6, 2012, 01:19 AM
Today my son and I made some fairly long target practice hits from the top of a hill side to the bottom. Distance guesstimated ~500yds. The line of sight angle from our position to the valley floor looked like ~45 degrees. He was shooting factory 165gr. loads, 180gr reloads (30-06) for me. The lack of bullet drop has made me curious.
Does anybody know of a "rule of thumb" or estimate of this effect?
Two other (hunting) occasions this has surprised me, once uphill, once downhill. At those times, the target was much closer, 100-150 yds.
Sorry I don't have more exact numbers, we don't have a rangefinder, though I'm thinkin' one would be usefull to help me learn more about shooting beyond 2-300 yds.
The rangefinders I've looked at cost about as much as a rifle :cuss:.... Or, those dollars could buy a whole lot of practice ammo!

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allaroundhunter
August 6, 2012, 01:37 AM
What you are asking about is the true horizontal distance that the bullet is traveling and that gravity is acting on it. It is fairly simple to calculate if you know the angle and distance to the target and have a basic knowledge of trigonometry (your son will know it soon). Many shooting rangefinders have this ability now as well as just finding the distance to the target. Some will also be able to give you a rough estimate of your hold-over.

But yes, if your target is at an angle above or below you there will be a change in point of impact because the horizontal distance to the target is different than just the distance to the target.

Sent from my HTC One X

TonyAngel
August 6, 2012, 02:29 AM
Oh, yeah. I don't get too many opportunities to shoot from inclines/declines with my centerfire, but I shoot a lot of rimfire. When practicing for the championship match, which consists of four ARA targets stapled to the carrier one above the other, the targets span about four feet. I can definitely see the differences in trajectories when starting at the bottom target and progress to the top one. Four feet doesn't sound like much, but we are shooting at 50 yards and the 100 ring is about 3/8" in diameter, so its pretty easy to see the subtle effects.

If you want to explore this further without tearing your hair out, you can get an angle indicator which will attach to either your scope or your scope rail and use it in conjunction with a ballistics program on your smartphone, ipod or what have you. I think I paid $5 for the one I use on my Android phone.

chrome_austex
August 6, 2012, 12:29 PM
The easy estimate is to just use the horizontal distance, and not the straight line distance. That gets you really close. In reality, there is slightly more going on, I won't go into that right now.

So: Cos (down/up angle) * true distance = horizontal distance.

So, at 45' angle, 500y is more like the drop for 350y.
30' angle at 500y is like 433y
10' angle at 500y is like 492y (and you can see that anything less than about 10' gets pretty minor).

Float Pilot
August 6, 2012, 12:34 PM
The drop of the bullet over a horizontal distance is the same.
So instead of having the drop it would from point A to point @@ on my graph, it drops the same as it would from point B to point @@.
If you shot straight down the cliff from Point A to point B, then there is no drop since the bullet is heading straight towards the earth. If you shot at a fairly steep angle from point A to point T, then the bullet drop is only the same as it would be from point B to point T. A very short distance.


Top of cliff
A
X
X
X
X
X
X
X
X
X
X
BOOOOOT[/B]OOOOOOOOOOOOOOOOOOOOOOOOOOOO[B]@@TARGET

Zak Smith
August 6, 2012, 04:37 PM
Here is the reference
http://www.exteriorballistics.com/ebexplained/article1.html

Reality is not quite "horizontal distance" but that's better than no correction

SharpsDressedMan
August 6, 2012, 05:30 PM
Aim low, cause your gonna hit HIGH! If your shot was 500 at that angle, and the table shows 350, you only need holdover for 350. Gravity is only affecting the bullet for 350 yards.

Flatbush Harry
August 6, 2012, 05:34 PM
Look at Craig Boddington's article in the current issue of Guns and Ammo. The adjustments for angles are the same for up and down angles.

FH

Centurian22
August 6, 2012, 09:04 PM
If you have an iPhone (might be available on other smart phones as well I don't know) look into the app "iStrelok", it's a ballistics app that allows you to plug in the angle of the shot. Fun to play with different distances and angles to get an idea of where you'll hit. There is also a rangefinding app called "spotter" which is helpful.

Best of luck to the OP and thank you to everyone else who have shed light on this phenomenon. I knew that there was less drop but never knew the physics of why. Gravity only acts on the horizontal distance (basically).

greyling22
August 6, 2012, 09:11 PM
rule of thumb: your shot will go high when you aim downhill. (I first learned this in elementary school in a louis l'amore book.) I believe it also applies to shooting uphill.

rodregier
August 6, 2012, 09:14 PM
http://www.longrangehunting.com/articles/angle-shooting.php

http://www.mildot.com/

Additionally, angle of fire for uphill or downhill shots can be accurately measured, and the up/down compensation can be closely calculated to reduce the errors such shots can induce.

7mmstalker
August 7, 2012, 10:38 AM
Wow, good stuff, thanks for that.
Going to check out the G&A article by Boddington.
The shortcut method of using horizontal distance to estimate hold-over seems adequate for what we do.
Since I've brought my son out in the field, my time and energy for reading and reloading has been in short supply. You'all have helped us both towards better shooting and more ethical hunting.
This site and the discussions are an excellent resource, again, thanks to all who replied!

jim243
August 7, 2012, 11:47 AM
I believe it also applies to shooting uphill.


I always thought it was, Shooting downhill hold low, Shooting uphill hold high?this is wrong

Jim

H&Hhunter
August 7, 2012, 01:14 PM
I always thought it was, Shooting downhill hold low, Shooting uphill hold high?

Jim

NO NO NO NO.......:)


Downhill OR uphill you hold low.

The hold for a 45 deg downhill shot at 500 yards is EXACTLY the same as one for a 45 deg UPHILL shot.

The only thing that matters is the angle it makes no difference whether or not the bullet is traveling up or down.

jmr40
August 7, 2012, 04:19 PM
The difference is pretty small with modern rifles until you get into extreme ranges. But yes the bullet will "appear" to have less drop whether you are shooting uphill or downhill. The real reason is that because of the angle, the bullet is actually traveling less distance than it appears. This is actually more of a concern with archery hunters shooting from high treestands. The arched trajectory of arrows, combined with the steep angles make it a problem there.

Look at Float pilots graphic. A range finder will show the range from top of cliff to target. But in reality the bullet only travels the distance from the base of the cliff to the target.

It would be the same if you were shooting from where he has placed the "target" up to the top of the cliff.

You could use a ruler on your screen to measure the actual differences if in doubt. Doing that with 1"=100 yards I get 4.5" or 450 yards from "A" to target, but only 4.25" or 425 yards from "B" to target, which is the actual distance the bullet would travel.

A 25 yard error in range estimation is only starting to become a problem at around the 400 yard mark. For most rifle shooting this is really not a concern.

Float Pilot
August 7, 2012, 06:51 PM
A 25 yard error in range estimation is only starting to become a problem at around the 400 yard mark. For most rifle shooting this is really not a concern.

Except when I make long-range shots with my 50-90 Sharps or my 45-70 carbine in places like this...

The distances are further than they look in this photo, and I am no super long range competitor like Zak Smith

After climbing the ridge on the left, (the lowest bushes in the photo are chest height) I looked back and saw a HUGE moose back down on the bottom of the meadow (there is a creek bed in there which has cut a winding groove feet deep into the ground, not counting the bushes above it) ....
My range finder said 425 yards....Which I can do with my Sharps,,, on a level range....
But according to my spotter, my shot whistled right over his shoulder by at least a foot.... Then he made the jump to hyper-space...

http://www.thehighroad.org/attachment.php?attachmentid=169578&stc=1&d=1344379776

H&Hhunter
August 7, 2012, 07:23 PM
Except when I make long-range shots with my 50-90 Sharps or my 45-70 carbine in places like this...

The distances are further than they look in this photo, and I am no super long range competitor like Zak Smith

After climbing the ridge on the left, (the lowest bushes in the photo are chest height) I looked back and saw a HUGE moose back down on the bottom of the meadow (there is a creek bed in there which has cut a winding groove feet deep into the ground, not counting the bushes above it) ....
My range finder said 425 yards....Which I can do with my Sharps,,, on a level range....
But according to my spotter, my shot whistled right over his shoulder by at least a foot.... Then he made the jump to hyper-space...



Float Pilot,

That picture just caused me an instant, almost uncontrollable compulsive urge to quit my airline job and move back to Alaska!

7mmstalker
August 8, 2012, 12:42 AM
H&H Hunter......
Go with your gut and do it!
A school buddy talked me into coming up "for the summer", nearly 10 years later my wife said we had to go back to WA state (home & family) before she would submit to my demands to procreate. Now, 11 years later, SHE wants to go back up north!!
Being in the airline industry is one of the better situations for experiencing Alaska. You guys can commute on jump-seat passes. Keep your main residence in the lower 48 and rent a room up there for work and play.
Anchorage is a hub airport for a lot of Eastern European cargo routes. Many international carriers operate there. Fed-Ex and UPS had major air cargo operations bases when I was there, 91-2001, likely still going strong. Passenger routes, not so much. Not sure, but seems that Alaska Airlines has the biggest share of domestic passenger routes.

Edit: Just re-read your post, you said "back to Alaska" maybe you know these things already!



Float Pilot,
One of the field shots that was almost missed because of this was in your back yard. Drew a permit to hunt mountain goat on the east side of Sadie cove. One of those critters looked over a ledge above me, not much more than 100 yds away. All that was showing was his chest and head, so i aimed at the brisket and sent some lead up there. The bullet impacted between the eyes, and exited under / behind one horn. They say those goats are tough to anchor, not this one!
That was also my first, and only, float plane trip, short, but probably the best airplane ride of my life. In a Cessna with stick controls and a powerful 6 cylinder engine, also had the "greenhouse windows" in the top of the cockpit. When the pilot banked around hard to head home, looking at the glacier from those windows felt like you could almost reach out and touch the snow! It reminded me of my first time ever in an airplane, at about 8 yrs old. Words fall short of describing that feeling.

Float Pilot
August 8, 2012, 01:19 AM
Unfortunately we have been flooded with job-less folks over the past few years. (2009) The type who are not looking to be employed, nor have they ever been. The States who were running out of money for their various welfare programs have been buying them tickets here...

So we need folks like you who know how to work and who do not vote against the 2nd amendment.

7mmstalker, you were probably flying with Jose DeCreeft in his L-19 Bird-dog...

My summer office.....

http://www.thehighroad.org/attachment.php?attachmentid=169592&stc=1&d=1344403094

7mmstalker
August 8, 2012, 02:16 AM
You are in god's country there man!!!
Seemed like the deadbeat types were getting a foothold when we were there, sad.
That name sounds vaguely familiar, but the L19 Bird dog I'm sure of. Not a common airplane is it? Seems like he was part of a family operation, most of their clients had bigger budgets and flew in an Otter if I recall. After that memorable take-off, we saw the big Otter coming in under us to pick up another group. Even from far above it looked huge, flying low.
Nice Cub, love that traditional color scheme. The ultimate "fishin' and huntin' rig" for Alaska.

H&Hhunter
August 8, 2012, 10:19 AM
Edit: Just re-read your post, you said "back to Alaska" maybe you know these things already!


7MM,

Yep I started off flying for Ryan Air Alaska In Kotzebue, Aniak and Nome then got hired out of Deadhorse flying for a company doing contract work with the USN in the winter and was an AK Smokejumper pilot in the summer. I put in five seasons and had never planned on moving outside. The I got laid off was going broke one winter and got a job offer down in NM flying for an oil company. So I took it with plans to make it temporary. The rest is history!

Stuff happens and here I am.

7mmstalker
August 8, 2012, 10:53 AM
New Mexico was once on our short list of places to consider if we bug out of WA.
A retired fellow was telling me that living in the higher elevation will get you a four season climate, and some decent hunting. But, I have grown accustomed to the coastal humidity and mild summers. Hot weather above 75 - 80 melts me.
The politics and personalities in most of western WA are a tough pill to swallow, but the jobs are here. So as you say, here we are.
I keep hearing about similar social decay in so many states, we are not unique here, maybe just more concentrated. There are a lot of good people here and a great shooting range 5 min. down the road.
After a couple years of trying, we are finding some deer, Elk are here but too few for much opportunity. My son the new hunter and I bought bear tags this year, we'll see how that turns out.
Hard to compare the hunting in general to AK.
One weekend, two buddies and I bagged over 40 snowshoe hare - many using a handgun- left quite a few there to make more . They must have been at the height of a population boom cycle.
Off to work, happy trails to all!

H&Hhunter
August 8, 2012, 11:35 AM
Good luck on your hunts this year!

hang fire
August 8, 2012, 03:18 PM
The dead beats in AK go back over 40 years when we lived there, saw the hippies out in Unalaska on the Chain. We lived in rural area down on the Kenai, mile post 36, Seward HWY and they were a constant pest. Hearing their first wolf howl, they were beating on the door wanting to know if they could sleep on the floor or out in the feed shed. I got transferred in 1976, so followed paycheck outside.

Our backyard: http://hstrial-rchambers.homestead.com/lpic_op_577x600.jpg

Silver salmon to be cleaned: http://i3.photobucket.com/albums/y92/TANSTAAFL-2/Salmon3.jpg

http://i3.photobucket.com/albums/y92/TANSTAAFL-2/Salmon4.jpg

Spring breakup: http://i3.photobucket.com/albums/y92/TANSTAAFL-2/SlidesBox15073.jpg

1858
August 8, 2012, 04:13 PM
Reality is not quite "horizontal distance" but that's better than no correction

Exactly. Using the horizontal distance method is an approximation. 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).

7mmstalker
August 8, 2012, 10:13 PM
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
August 8, 2012, 10:20 PM
Really love this guys videos, he's a very good teacher.

http://youtu.be/wTSBcNgGMNo

Centurian22
August 11, 2012, 10:22 PM
Awesome video explanation!!! Thanks!

ShadowsEye
August 12, 2012, 02:29 PM
Awesome video explanation!!! Thanks!

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

1858
August 12, 2012, 03:19 PM
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.

1858
August 12, 2012, 03:35 PM
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
August 12, 2012, 08:00 PM
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.

1858
August 13, 2012, 11:51 AM
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.

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