Uphill/downhill shooting

D

DonV

Guest
Uphill/downhill shooting

Did anyone catch the article in the dec issue of huntin fool? Very good info, I was way off, I figured if you took a steep shot you calculate the horizontal distance the bullet travels and then hold for that elevation and shoot. For example if the shot was steep uphill and the game was 500 yards away but was only 300 yards horizontal you held for a 300 yard shot, not true.

It was very eye opening.
 
Long story short most know that bullets only drop proportional to horizontal distance traveled. What was knew, and very very important was that the distance also affects bullect impact. Reason is bullet still travels entire distance so where your sights are do affect where the bullet hits.

For example if the game is 500 yards away but only 250 horizontal, your bullet drops 250 yards worth from gravity BUT your bullet still travels the entire 500 yards, thus diverging twice as far from your line of sight as it would at 250 yards, this comes into play and makes a huge difference.

Very hard to explain, I read the article twice and I took a ton of math/physics in college and still am not 100% sure I understand it right. Bottom line is simply holding for horizontal distance and shootingcan cause big misses at long range and steep shots.

I have noticed many many times when reading about long range hunts when guys hit high and wondered why they never took into account angle enough, now I know they did take into horizontal gravity aspect but not the fact that the bullet still travels that distance.

They had several examples, at ranges of 300 yards and beyond and angles of 45 degrees and more suffice to say that simply holding for the true horizontal distance causes your bullet to hit high, and it can easily be 8" or more high, it was very eye opening.

Suffice to say if you ae shooting at a dall sheep at 60 degrees above/below you and 400 yards away (line of site), if you are zeroed for 200 yards and simply hold for the true horizontal distance of 200 yards you will hit high by many inches, not dead on as you would think.

I was going to buy an optilogic rangefinder which can calculate true horizontal distance but now I am not going to since it will not take into account what I have mentioned above. I will use a program and make a chart and tape it to my gun, a lot cheaper and a lot more accurate.

The article is a very good read.
 
In your 500/250 yard example the bullet travels through 500 yards of air ... that is ALOT of slowing down and shows why using a 250 yard estimate, where the bullet slows down a huge amount less, is wrong.

Bows are so slow and the range is so short that really using the "horizonal distance" rather than pure distance from say a tree stand, works out pretty close. The arrow doesnt slow down enough either way to really account for much of a change in POI.

The whole angle thing is indeed hella-complicated and I havent totally solved it to an acceptable degree to allow me to put it in PointBlank.


-DallanC
 
You are right Dallan but in your statement that the bullet slows down - you would think the bullet would hit lower not higher, yet another reason many fail to realize what is really going on.

Bottom line is you need to account for the shorter distance AND hold low above and beyond that adjustment. Tough to make yourself do after years of accounting for elevation by holding high, I have never had to aim low in my entire life.

I was wondering about a bow, I suspect since we have multiple pins it minimizes this discrepency.

I wish I could get permission to print the article here.

Again I am sure without reading this article when I finally draw a ram tag and if I take my rifle I am sure I would have shot high. Good info.
 
Ok I will take a shot at this. I think the critical thing about the angle is the effect of gravity across the shot plane. Simply, if you shoot straight down or up the bullet does not drop. Yes it slows down going up, untill it stops. Friction with air does slow down the bullet and on the the flat plane, gravity has effect on the drop. Air density also changes things. Bullets drop slower at high altitude. I have found that it does not make enough difference to worry about.Shot a pig at 408yds on Sunday, up hill 45 degree and never worried about it. Bingo one shot.It is fun to think about this stuff, even if we do not hold degrees in Physics!
 
Blueoak that is what I used to think but it turns out that the true distance does make a big difference, simply put just holding for the actual horizontal distance is NOT enough. At long ranges and steep shots when you think your bullet will be dead on it can be 1 foot or more high.

This is why I posted, I bet 99% of hunters have no clue about this, heck it is easy to see when you read tons of articles about mountain hunting, guys who know their guns and take into acount angle still miss high. I alwasy thought they just screwed up and forgot to take into account the angle, now I know they may have and still missed high.
 
I'll take a shot at this, too...

In theory, without taking into account the additional slowing of the bullet due to wind resistance, the actual bullet drop of the angled shot is the same as the actual bullet drop at the horizontal distance. But the bullet drop I'm talking about is not where the bullet strikes in relation to your sights, but where the bullet is in relation to the line of the bore. If your rifle is sighted in 2 inches high at 100 yards, then the line of your bore is actually angled up from the line of sight. A 300 yard level shot might hit 6 inches low. But if you shot at a target 300 yards straight up (or down), the actual bullet drop (in relation to the line of the bore) would be zero, so the bullet would strike much higher than your line of sight (the aiming point)...probably by as much as 6 or 8 inches. Any shot between 0 degrees and 90 degrees, the effect will be the same...but only to a lesser extent.

To acurately calculate the bullet impact in relation to your line of sight while shooting at an angle, you would need to know where the line of your bore is at the given range in relation to the line of sight, as well as the amount of actual bullet drop at the horizontal distance of your shot (in relation to the bore, NOT the trajectory of the bullet as you sighted in). Subtract the actual bullet drop (horizontal) from the amount the line of your bore is above the line of sight, and you will know where the point of impact will be in relation to your crosshairs.

Once again, this does not take into effect the additional decrease in velocity from the increase distance of the sloped shot versus the horizontal distance, but I think, for hunting purposes and shots under 500 yards, the difference will be minimal.

That's my theory, anyways...
 
if you're sneaky enough all you have to worry about is powder burns. you guys are gonna fill yer heads fulla so much info that while you'e doin' the calculations, the deer'll run off. it is an interesting subject, but with most of todays modern cartridges in a good rifle, it takes most o' the guess work out for ya.
 
Not everyone uses rifles for only shooting game. Competition shooting is quite popular, in fact I have several regular posters on my website that shoot around 1000 rounds a month (and 2 guys that do that much per WEEK). Discussions like this are quite interesting and quite relevant.


-DallanC
 
Like RLH says modern rifle calibers take a lot of the guess work out of the equation, but if the angle is really steep (up or down) take the old advice of holding LOW on steep shots.

Phantom Hunter
 
Having grown up in Ohio (no rifles allowed) long range shooting is 100 yards. Shots at 300 yards seem to me VERY far. I have only hunted with a rifle 3 times for big game. When I do go on some really big hunt where a loooong shot might happen I will practice a alot and if everything is perfect I might shoot at 400 yards.

As others above mentioned most modern rifles are fast enough to minimize what I am talking about - enough not ignore it, especially on elk size game.

But if you are shooting at sheep or antelope and the angle is 60 degrees or more and the shot at 400 yards or more the difference is enough to miss. I realize the combination of these all occuring at once is remote, most likely you just need to worry about true horizontal distance. I plan to add 1 or 2 figures to my "cheat sheet" that will be taped to my stock when I go on a big hunt. In addtion to wind adjustments, elevation for long shots and angle adjustments I will include one of these.

More often I use such a chart to look at while taking a break and have the more likely scenarious memorized. But you never know when you might be perched way above a nice sheep and have hours to do the math and consider the shot.

Good input guys and again I far from fully grasp this concept, I just thought it was important enough to let everyone know.
 
For me it's a matter of practice. There are many things to influence long range shots, including altitude, barometric pressure, wind, degree of angle, etc. Out to 200-400 yards the effects are minimal, but reaching out there to 700-1000 yards is another story. My furthest killing shots on deer have been 450 yards and coyotes out to 550 yards. But, I'm builing a long range gun as we speak and when finished I'll be shooting that thing at every chance I get, just to find out what it'll do at extreme ranges. It's not unethical if you know you and your guns abilities and don't go past them. It's just a matter of practice...Steve
 
Here in Ohio practice past 100 yards is tough, past 200 I know no where with a range that long. I have never shot past 200 yards in my life, simply because I cannot, sucks, one reason I am reluctant to shoot past 300 - I simply cannot practice that far. You guys that can are lucky!

I know a lot of hunters who are unethical to shoot past 50 yards, but they do! It all depends on how familiar you are with your weapon and that particular shot.
 
Don-
haven't logged on in awhile, but finally got a chance and saw this post. I am really tired right now so all that math is a bit confusing. I had a shot this year that was about 225 yards. It was downhill and fairly steep. Hard to calculate in the moment, but when its the fourth day on a five day hunt and you've got the first bull you've seen, in your sights, you get to figuring real fast. I aimed about four to five inches above the bottom of his his chest, right behind the shoulder and dropped him in his tracks. But, I hit him in the spine and the bullet deflected down and took out a lung and then some. I was surprised at how high my hit was. I will check out that article when I'm thinking clearly. Always got to think about those hard shots. There is always some little complication.
 
Link to shooting uphill/downhill discussion.
http://www.exteriorballistics.com/ebexplained/5th/33.cfm

After reading this , I pulled out my old Sierra reloading manual and looked in the exterior ballistics section and did some computing. I used a 180 gr SBT (bc=.537), @ 3000fps, zeroed @ 250 yards, as my basis (similar to 300 win mag). I did calculations for a 500 yard shot downhill at 45*.

At 500 yards horizontally, the bullet drop from boreline is 59.5" and the bullet path relative to line of sight is -31.9" With the 45 degree angle, the bullet path is raised 17.4", making the bullet path at the target -13.9"

I calculated the horizontal distance to be 354 yards. The bullet path at 350 yards when angled 0* is -7.9" So it appears to me that if you held for the horizontal distance, you would hit LOW since the path is 6" lower than a horizontal hold at 350 yds. The -13.9" path looks to match about a 400 yard hold, not the 354 yard horizontal distance. Even holding for the horizontal distance appears to be in error.

RR
 
Wow! I tried to concentrate on that article but still got lost. Any body have some plain English explinations for us dumb ones. I will throw out some fake numbers just so I can try to get the general priciple down and worry about exact numbers later. Remember these number are not real.

Fake situation: At a flat zero degree angle gun is sighted in at 250 yards. To hit the bullseye at 500 yards at a flat zero degree angle in this situation I must aim 30 inches above the bulleyes.

Now without adjustments to the scope I now shoot 500 yards uphill at a 45 degree angle. To fit this concept do I:
a)still aim 30 inches above the bulleye?
b)aim 20 inches above the bullseye?
c)aim 40 inches above the bullseye?
d)or aim below the bullseye?
 
LAST EDITED ON Dec-16-05 AT 11:51AM (MST)[p]THOSE CHEATING SONS OF XXXXX's!!!

LMAO thats a slick trick they used there to "approximate it".

If you guys knew how many hours I've wasted over the past 3 years trying to calculate this precisely for PointBlank. I tried tackling it from a pure physics model, trying to track how gravity G applies to Vy and Vx of a bullets velocity (its a differential equasion), and figuring in atmospheric changes etc etc (there are another dozen variables to truely track a precise trajectory). All my attempts were pretty close but it always failed in a few cases and I was never totally happy with it. Their trick seems pretty close now that I run some calculations.

I like how they just say:

"There are two other smaller effects on drop as the bullet travels. When a bullet is traveling upward on an elevated trajectory, there is a component of gravity that adds to the drag deceleration of the bullet, but the bullet is traveling into less dense atmosphere that reduces the aerodynamic drag. So, these small effects tend to offset one another."

Or in other words, screw it, its close enough. R_O_T_F_L!!! That totally cracked me up. I've been wading through that crap trying to solve it (not trivial!!) I guess thats what I get for trying to be precise.

...

Look for ANGLE calculations in the next version of PointBlank (rewriting it as we speak in my spare time... should be ready in a couple months).

Thanks for the article redrabbit... been beating my bloody head against the computer for a couple years trying to solve it.

Heres a pict of me trying to solve it with a true physics model in my spare time:

slamhead5uy.gif


:p

-DallanC
 
Dallan,

I e-mailed Sierra regarding my calculations to see if they are correct and how to calculate what to hold for at various ranges and angles. Waiting on a reply.

I like your point blank program, and hope you can get that bloody mess off your keyboard.

Doug~RR
 
donv were at in ohio are you located at i live in ohio and the gun range i shoot at is putting in a 500 yd range its going to be the longest in ohio besides camp perry its sandusky county sportsman club
4209712115a8bdc2.jpg
 
No point in trying to get it too exact. Wind drift is even more of a guess at the longer ranges. The bottom line is that lots of people are really fooling themselves about their long range capabilities when you throw in real things like uphill/downhill and wind drift. The more you actually shoot under those conditions, the better, but who does that?
 
I live between cleveland and akron.

Dallan that is funny!

I do agree with all that this only affects things at long ranges, for me further then I am ever likely to shoot.

redrabbit, intresting what you calculated I expected a higher hit not lower, but still the point is valid, simply holding for true horizontal distance is not enough in your scenario.

Trey, I here you, I get a headache just trying to figure this out. Very confusing.

Again one thing that hit home for me is how many guys I here about who hit high at steep angles & long range. Guys who understand the adjustment for angle. This article made me realize why. From my own informal reading I would guess 3/4 or more of high/low misses at long range and steep angles are high.
 
huntin fool is a pricey magazine that provides a lot of statistics for draws in every state, pretty serious big game, pack in, high dollar magazine.
 
Ok, I think I understand how to calculate the appropriate adjustment to where your bullet will hit, based on the formula that the adjustment = do [1-cosineA]. What I'm still not clear on is whether this adjustment is applied to where your bullet would hit based on the ranged distance to your target (ie, uphill or downhill) or the horizontal (level) distance to your target.

To illustrate, consider the following scenario:

Your gun is dead-on at 250 yards level distance, and is 10 inches low at 400 yards level distance. You are shooting at the nomad buck at a ranged distance of 400 yards up the hill, which works out (coincidentally, because I'm trying to keep it simple) to 250 yards level distance. Assume the adjustment = do [1-cosineA] = 6 inches. Do you now hold 6 inches low or 4 inches high? In other words do you adjust for the point of impact of 0 inches low based on a level distance of 250 yards, or for the point of impact of 10 inches low based on the ranged distance uphill of 400 yards? Since the nomad buck is only about 10 inches deep from the top of the back to the bottom of the chest, where I, oops, I mean you, hold could mean a miss instead of collecting a spike . . . er. . . trophy buck.

Can anyone help me out on this one?
 
bcmulie I wish I could, but if I was that smart I would not be typing this I would be on my 2 month, round the world hunt.

You know understand what to take into account - but how much is the big question, from the limited tables the article provided I know typically you need to hold a little low, in your case maybe 4-6", but that is only a guess. Sorry, but at least you know now to look around.

When I do go on a hunt where this might occur I plan to find some stats and tape a couple to my stock, and if required take a quick rough guess, better then nothing.

No you see why Dallan is bashing his head on the keyboard!
 
LAST EDITED ON Dec-20-05 AT 11:01AM (MST)[p]You dont have enough info, we need to know the total drop at the 400 yard range.

The angle we know as 51 degrees up:

sqroot( 400^2 - 250^2) = 312 yards vertical
atan(312/250) = 51 degrees

*Guestimating* a velocity and BC to hit the trajectory you give:
(bc = .50, velocity = 3450) we get a total drop at 400 yards of -27.7"

From there its now simple to compute. Your horizonal trajectory is -10.61 so running the new angle calculation we arrive at an ajusted drop of -.342"

So with a 10" killzone if you held more than 5" high or low you would miss. In this case sighted in at 250 yards shooting 51 degrees up with a bullet of .50BC going 3450fps you would aim dead center to hit it.


-DallanC
 
DallanC, I just went back and read my post and realized that the formula I had in square brackets didn't appear in my post. The adjustment should have = do(1-cosineA), per the Sierra website. If I'm understanding correctly, in your post you've figured out exactly what "do" (the total drop) and the angle would have to have been based on my invented numbers. You've then rerun the calculation, adjustment = do(1-cosineA). Do I have that right?

From your post, I take it that the adjustment is applied to your point of aim. In other words, I should aim 0.342" above my target for a direct hit? That's really the question I have - namely, do I change my point of aim based solely on the "adjustment" (-0.342"), or based on the "adjustment" added to where my bullet strikes at 400 yards relative to my line of sight (-0.342" + -10.61" = approx -11")?

DonV - I'm with you printing out a table. Right now I have a trajectory table taped to my rangefinder, but it doesn't have adjustments for angled shooting. I'd like to add that in once I understand how it all works.

Thanks guys.

bcmulie
 
>in my post. The
>adjustment should have = do(1-cosineA),
>per the Sierra website.
>If I'm understanding correctly, in
>your post you've figured out
>exactly what "do" (the total
>drop) and the angle would
>have to have been based
>on my invented numbers.
>You've then rerun the calculation,
>adjustment = do(1-cosineA). Do
>I have that right?

do(1-cos(a)) = the amount the bullet flys high when shot at an angle. You take the ABS value and add it to the horizonal drop of your trajectory.

In the hypothetical case above you said zero'd at 250 yards, at 400 yards you are -10" low. Calculating the amount the bullet flys high while shooting that steep angle, we find it shoots 10.61" high. So add the two together we get the number I quoted. Note you never gave me ballistics info such as BC and velocity so I guessed on those to make a trajectory that fit the 250 zero, 10" low @ 400 so the numbers arent exact... but its within an inch.

51 degrees up is damn steep though and you are shooting a *really* fast rifle with *perfect* bullets to get a trajectory like that too...I know its hypothetical but wow.


>From your post, I take it
>that the adjustment is applied
>to your point of aim.
> In other words, I
>should aim 0.342" above my
>target for a direct hit?

No. Aiming directly at the Nomad, 400 yards away at an angle of 51' vertical your bullet hits .342" high from your point of aim. A slower more realistic shooting rifle would show a much greater difference in PoA vs PoI.


>DonV - I'm with you printing
>out a table. Right
>now I have a trajectory
>table taped to my rangefinder,
>but it doesn't have adjustments
>for angled shooting. I'd
>like to add that in
>once I understand how it
>all works.

This is a feature people requested for PointBlank v2.0. They want a small 1x4" trajectory table they can print and tape to their scope / stock. I'll be adding it.


-DallanC
 
DallanC, thanks for clarifying. To be sure I've got it clear, my understanding of the applicable formula is as follows:

X = Y - do(1-cosA)

with the variables defined as follows:

X = where you should aim for a direct hit

Y = bullet drop from line of sight at the ranged (rather than horizontal) distance to the target

do = bullet drop from the bore at the ranged distance

A = angle at which you are shooting

Do I have this right?

Also, I'm not familiar with PointBlank. Is this a ballistics program that you developed? If so, when do you expect to have version 2 completed, and how can I get a copy?

Thanks again for your help. I'm sure we're boring lots of other MM members, but I personally find this quite interesting. :)

bcmulie
 
>Do I have this right?

Yes. Most all of this data except for the do(1-cos(a)) is all calculated in PointBlank

>Also, I'm not familiar with PointBlank.
> Is this a ballistics
>program that you developed?
>If so, when do you
>expect to have version 2
>completed, and how can I
>get a copy?

I am surprised you havent heard of it. Its one of the most popular Ballistics programs on the net... the free price tag might have something to do with that :). Its been around for 5 years now... geeze almost 6 now that I think about it.

Its available at my website, www.HuntingNut.com.

Whats amusing is I've gotten emails from people who asked Sierra for a cheaper option to their Infinity program and they always point people to PointBlank.

I am just beginning the re-write of v1.8 to include all the feature requests people have been bugging me with for the past couple of years. Adding in angle calculations to it is EASY.

Oh yea I wrote a PHP version of PointBLank that works online but you have to register with the site to access it (site is free).


-DallanC
 

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