Not grasping the basics of shooting up and down hill

[chutestrate]

You want to aim lower for a downhill AND uphill shot? I struggle with geometry and this makes no sense to me.

If I use a rangefinder and see a whitetail 100 yds out downhill my instinct is to aim slightly higher.

Is there a practical approach to doing this in the field on the fly?

[NSB]

At 100yds on a deer there is no practical reason for doing it. Any difference in trajectory will be minute.

[youngda9]

It's basic trig...A refresher:

Gravity is always pulling straight down and will accelerate your bullet in the downward direction only. If you shoot from a horizontal barrel and the bullet flying parallel the force on the bullet is G*sin(angle). If the angle from the barrel to the force of gravity is 90degrees...then the force on the bullet is G*Sin(90) = 1G. All of gravity will be affecting the bullet "drop" ("drop" is in relation the barrel, which in this case is horizontal).

Now let's say you fire the bullet down a hill at a 45 degree angle. G*Sin(45)=0.707. In that case the bullet "drop"(in relation to the barrel) will be 0.707 times that of which it would be had the bullet been fired horizontally(from the previous example).

Basically any time the bullet path is not horizontal gravity can be is broken into two vectors. One is bullet "drop" (in relation to horizontal flight) and the other tangent tries to accelerate (if the bullet is traveling downward) or decelerate (if the bullet is traveling upwards).

[DougGuy]

Basically, like youngda9 said, gravity only pulls it's strongest when the boolit is fired horizontally, or parallel with the earth's surface. Any time you shoot either uphill or downhill, gravitational pull is diminished, because it's pulling at an angle and exerts less pull on the boolit, therefore causing the boolit drop to be considerably less than when fired horizontally. Since that results in the boolit's point of impact being higher on the target, then you should hold under no matter if you are shooting uphill or downhill.

Boolits travel in an arc or curve, because of the force of gravity pulling against them.

Example: If you shoot a 180gr boolit, @2400f/s in a .308 that is zeroed @200yds, then at 100yds, it will be about 1.5" high. This is perfectly normal trajectory and you would want to remember to hold 1.5" low @100yds for the boolit to strike at intended point of aim. Were you shooting uphill at a steep angle, or downhill at a steep angle, you may want to hold 2.0" to 2.5" low @100yds to compensate for a reduced gravitational pull, but since the rifle was zeroed @200yds, you would only want to hold about 1.5" to 2" low @200yds to strike the intended point of aim.

[300savage]

A far easier way is if the game is higher than you whatever the distance would be if you were to drop a line from him straight down until it was on your level, that's your true distance. So if he is 300 yardsmeasured yards from you on a slope, but only 200 to where he would be if the ground were level, don't aim low, instead just shoot for 200 yards. Works the same up or down.

The only factor other than that to consider is that the animal is still standing balanced with gravity so if you put your cross hairs on his ribs mid body as perhaps you normally would because of the angle of his body in relation to your bullet path you could miss the offside lung. So you would aim lower, not because of the range nor angle of shot but because of the angle of the games body., conversely you would aim Higher on the body for a downhill shot, again because of the body position in relation to bullet path.

So there are actually two calculations to be made. 1 is actual distance, and 2 is body angle relative to bullet path.

[303Guy]

Just how much does the difference in bullet deceleration between shooting 45° up and 45° down make?

[felix]

Calculate the yardage the boolit will ACTUALLY travel (in air), and use that distance in the trajectory formulas. ... felix

[youngda9]

Just how much does the difference in bullet deceleration between shooting 45° up and 45° down make?
very little...not enough to worry about for 99.999% of all shooters.

[oldgeezershooter]

Most people think when you zero a rifle at 100yds. the rifle barrel is level.
It actually is aimed up a little because the bullet starts to drop the instance it leaves the barrel.
I argued with a friend that I could drop a bullet at the same time he fired a gun (Level) and they would hit at the same time. I think it's called physics or something.

[303Guy]

I think it's called physics or something.That was funny!:mrgreen: But it's not quite true.:roll: That's because a bullet actually 'flies'. It has lift. This lift develops as the trajectory increases and comes about as the bullet spin axis deviates from the line of flight. It also causes spin drift. Airflow forces the spin axis to tend toward the flight path. Not sure how much difference it really makes.

[youngda9]

The bullet drop theory is only valid if the fired bullet is shot in a vacuum.

[Outpost75]

A simple rule which works for most hunting rifles is one minute change for each 15 degree increment vector deviating fromthe horizontal, so a 45 degree uphill or downhill hold 3 minutes low, for a 30 degree up or downslope hold 2 minutes low.

You can do all the calculations if you want, but this was taught to me over 50 years ago by a PH, and has brought home lots of game shooting. 30-'06s and. 270s....

[Oreo]

Is there a practical approach to doing this in the field on the fly?

Ballistics calculator on smartphone. There are a few very good ones that can be pre-programmed with your specific load data / gun info / scope recticle etc. In the field you just punch in the distance and elevation difference and out pops the details complete with scope recticle image showing your holdover.

[ammohead]

Hunt to within 250 yards and none of this will matter.

[Mk42gunner]

Hunt to within 250 yards and none of this will matter.

Bingo.

Robert

[Bzcraig]

Poor guys question was pretty simple but the answers, as correct as most were, were still pretty complicated. I think DougGuy's answer was the easiest to understand with a good example for most PRACTICAL purposes.

[Hickory]

Boy, what a bunch of poluka.
There's only three here who would have a chance of getting a deer.
The rest of you be shooting into the hillside or into the sky.

[303Guy]

I can only recall one instance where I shot bad because I did not take the shooting angle into account and then I didn't miss. I hit the back of the head instead of the shoulders and what spectacular hit it was. It somersaulted the hare sideways. It turned the skull into an impulse engine by clipping the back of the head. But I digress. I do not know how to compensate for elevation. I never needed to really because my steeply angled shots were into trees and I had set my scope so it zeroed at tree hight and gave a midrange trajectory of 1¾" or so (which was the scope hight) at 110 yds.

[mroliver77]

Hunt to within 250 yards and none of this will matter.
That is unless you are mouse hunting and get a 250 yard shot up a 45 degree mountain! :kidding:
Jay

[RoyEllis]

The shorter the range to target and flatter the projectile's trajectory, the less compensation needed.
If you really want to calculate what "under hold" is needed, here's a table you can multiply the bullet drop @ range by to figure compensation. I can't imagine anyone needing to shoot over 45 degree inclination, but here it is up to max effective error angle.

UP / DOWN COMPENSATION FACTORS
5 Degrees: Drop Inches x .004
10 Degrees: Drop Inches x .015
15 Degrees: Drop Inches x .034
20 Degrees: Drop Inches x .060
25 Degrees: Drop Inches x .094
30 Degrees: Drop Inches x .134
35 Degrees: Drop Inches x .181
40 Degrees: Drop Inches x .235
45 Degrees: Drop Inches x .293
50 Degrees: Drop Inches x .357
55 Degrees: Drop Inches x .426
60 Degrees: Drop Inches x .500

[300savage]

Pretty simple really. Imagine a right angle triangle, you are at one point, your game is at the other, and the actual effect that gravity will affect your bullet is how far it is from you to the right angle of the triangle.
Which will be directly between said critter and the center of the earth..

[waksupi]

To expand on that. Imagine a right angle triangle, with the base being 6', the vertical being 8'. That would make the distance between the ends 10'. The 10' measurement is of no consideration, nor is the 8'. The only important distance is the 6', as that is the distance in which gravity will have an effect.

[popper]

Not grasping the basics of shooting up and down hill Muzzle up for uphill, down for downhill.:kidding:
Actually, as the chart shows, drop compensation is much larger. Unless you have the computer scope or are a sniper, it will still be gut and experience.

[Wayne Smith]

Basic rule - always aim at hair! As has been stated over and over, within about 200 yds it makes no difference, over that always aim at hair.

[MBTcustom]

Wayne, you miss the point. It's not a question of whether or not they are aiming at hair, It's a matter of which hair they are trying to hit. LOL!

This is a very interesting thread that I have enjoyed reading.
In case there are some who's heads have not exploded yet, I'll throw out one more variable for you.
Did you know that in a typical barrel the muzzle is sagging by .005-.012 inches as it is only being held on one end by the action? This changes the point of impact at 100 yards by about 1/2"-1 1/2" and is effected by gravity/angle exactly like everything else (less effect at elevated or diminished angles)? depending on your particular rifle, this can have a more dramatic effect on trajectory than anything else that has been mentioned.

There, now go bandage your heads, and just shoot the darn critters behind the front shoulder. LOL!

[Hamish]

To expand on that. Imagine a right angle triangle, with the base being 6', the vertical being 8'. That would make the distance between the ends 10'. The 10' measurement is of no consideration, nor is the 8'. The only important distance is the 6', as that is the distance in which gravity will have an effect.


DING! DING! DING! DING!!!!!! Wondered how long it would take before someone who can build a build a square outhouse would post,,,,,,,,,

[MT Chambers]

This all sounds like something outta "Best of the West"!

[Larry Gibson]

This is the way I understand it and works for me:

Gravity only works on a projectile the lineal distance traveled across the Earth/globe.

Uphill or downhill is not the same as lineal distance across the Earth.

For Example:
It maybe a 650 yards to the target, but only 500 yards across the Earth because of the angle of the shot.
Then 500 yards would be the trajectory calculated for.

Bill is essentially correct.

Over practical shooting distances (out to 1000+ yards) it is the horizontal distance, not the line of sight distance, to the target that determines hold over. Doesn't matter whether up or downhill.

If the target is at or under the zero range horizontally then aim normally unless the angle exceeds 60 degrees. If the angle of departure (up or down) is 15 degrees or less at practicall deer hunting/shooting ranges no correction is necessary. On smaller targets at longer ranges it is.

So to answer chutestrate's question; if your rifle is zeroed at 100 or more yards then you would not hold over or under. If looking up or down at the deer aim to put the bullet through where the heart lays.

My Leupold rangefinder, a watch and my smart phone all calculate for up or down shooting (its basically the same). Years ago I also developed a cheat sheet (chart) so with the guestimated line of sight and angle of departure it gave me the range to hold over for or to adjust the sights to.

BTW; a bullet in flight does not have "lift". That is a myth. Any decent book on ballistics explains it.

Also; the wind allowance is for line of sight. Thus for longer range shots up or down you hold (or adjust the sights) for the horizontal range but hold for wind using the line of sight range.

Larry Gibson

[303Guy]

Barrel sag! Now that's a consideration. Of course not all barrels are free floated but mine are. Barrel sag would have about the same effect as gravity on the boolit.

[Sweetpea]

Barrel sag! Now that's a consideration. Of course not all barrels are free floated but mine are. Barrel sag would have about the same effect as gravity on the boolit.

I drop a little blue pill into my bottle of Hoppes to counteract this...:guntootsmiley:

[300savage]

I drop a little blue pill into my bottle of Hoppes to counteract this...:guntootsmiley:

Best answer yet...

[303Guy]

BTW; a bullet in flight does not have "lift". That is a myth.No myth, I kid you not. The same force that turns a bullet to follow the line of flight is giving the bullet lift in the direction of the offset of bullet spin axis to flight line. Any modern decent ballistic book will explain it.

Here's how it is calculated;

80037

This is actually for cross-wind lift and can act downward or upward depending on spin direction relative to the wind.

Here's the link so you can see for yourself. http://www.nennstiel-ruprecht.de/bullfly/index.htm#Formulas

Note the title of the article; "How do bullets fly?"

[Beerd]

:veryconfu
..

[Larry Gibson]

303 Guy

I do believe you are confusing the lift of the bullet nose in flight with the lift as in an airplane wing. Note in your example in the absence of yaw there is no lift. Try Rinker's book on ballistics, it's an easy read. Your formula is for the force required to lift the nose. How much it's lfted depends on how much yaw there is. No yaw....no "lift".

Larry Gibson

[303Guy]

Nope, no confusion there. That is exactly what it is, lift as is found on an airplane wing although the mechanism is different. Downrange, the nose of the bullet is tilted up relative to the line of flight and this causes The Wind Force because the bullet is moving with a yaw angle through the air. And it does have yaw because the bullet is being turned to follow the line of flight but it lags behind. The following illustration shows that yaw or angle of attack shown by δ. The angle of the wind force, F1, acts rearward and upward, producing drag and lift.

80079

[Driver man]

My mind hurts now. I have found shooting across water can get ineresting results

[303Guy]

Shooting across water taught me how to shoot shotgun. It showed the shape and trajectory of the shot pattern. The rear of the shot pattern would hit the water first as it was travelling slower so dropped more.

Anyway, here is the uphill and downhill trajectory story if one can make out anything. It looked just like that in the article.

80086

[waksupi]

Shooting across water taught me how to shoot shotgun. It showed the shape and trajectory of the shot pattern. The rear of the shot pattern would hit the water first as it was travelling slower so dropped more.

Anyway, here is the uphill and downhill trajectory story if one can make out anything. It looked just like that in the article.

80086


The bottom of the pattern wasn't slower. It was lower!

[300savage]

OK,, just something for folks to think about but how far would a bullet drop if you were shooting 1000 yards straight down ???

[Larry Gibson]

OK,, just something for folks to think about but how far would a bullet drop if you were shooting 1000 yards straight down ???

Or how much "lift" would there be to increase/decrease the distance as 303s reference? 303 should resource more reliable ballistic references than simply on the internet. The answer to 300s question is obvious if he is refering to drop from the line of departure. If from the line of sight. ...then not so obvious.

Larry Gibson

[Larry Gibson]

OK,, just something for folks to think about but how far would a bullet drop if you were shooting 1000 yards straight down ???

Or how much "lift" would there be to increase/decrease the distance as 303s reference? 303 should resource more reliable ballistic references than simply on the internet. The answer to 300s question is obvious if he is refering to drop from the line of departure. If from the line of sight. ...then not so obvious.

Larry Gibson

[DougGuy]

OK,, just something for folks to think about but how far would a bullet drop if you were shooting 1000 yards straight down ???

Bleh.. 1000 yards!

[303Guy]

reliable ballistic referencesWould Nennstiel and Ruprecht be a 'reliable' source? If you have a look at the article I referenced you'll see it is the Nennstiel and Ruprecht work. Funny thing about internet searches and references on external ballistics is they often reference that same work by Nennstiel and Ruprecht.


If a bullet flies stable (gyroscopically and dynamically!) and the transient yaw has been damped out, usually after a travelling distance of a few thousands of calibres, the bullet´s axis of symmetry and the tangent to the trajectory deviate by a small angle, which is said to be the yaw of repose ....

80124

All bullets have a yaw of repose i.e. they all have yaw therefore, they all have 'lift'.


The Magnus effect in external ballistics, also known as 'spin drift'

The Magnus effect is what gives a bullet 'lift' which results in 'spin drift'. One should realise that such lift is not in the vertical plane but sideways. Wind gives a bullet a vertical lift lift component but it is less than the horizontal component.


In January 2009 the Finnish ammunition manufacturer Lapua published Doppler radar test-derived drag coefficient data for most of their rifle projectiles.[17][18] With this Cd data engineers can create algorithms that utilize both known mathematical ballistic models as well as test specific, tabular data in unison. When used by predicative software like QuickTARGET Unlimited, Lapua Edition[19] or Lapua Ballistics[20] can be used for more accurate external ballistic predictions.

Notice how recent this is? There are older studies but not all that old. Thing is, all good ballistics references are recent. Some available references are wrong to some extent.


The writer has performed this study, mainly using Modern Exterior Ballistics by Robert L. McCoy, but with the aid of other references also. Mr.
Hollister’s observations are correct. Section 4.3 of the Exterior Ballistics chapter of the
Sierra Rifle and Handgun Reloading Manual, Edition V, is not correct.

Exterior ballistics is a science. Studies have been conducted and maths applied.

[303Guy]

Here's a curious one; Does a head wind make a bullet shoot higher or lower?

Well, guess what, a tail wind will make a bullet shoot lower than a head wind!

We know from the experience of others if not our own that cross wind effects are not horizontal but angled and the angle depends on the spin rate and the direction of spin.

It's also true that the same speed and angle of cross wind affects wind drift more in on direction than the other. That's due do wind drift being added too or subtracted from spin drift.

P.S. My apologies to chutestrate for drifting off topic (excuse the pun). I doubt any of the above is relevant to shooting uphill or downhill although wind drift might be a real concern at longer ranges on small critters.

[Duckiller]

303 guy you have more expensive rifles than I do. My 03A3 that shoot 2-3 inches at 100 yds doesn't have any lift that I can measure. Airfoils are not symetrical about a horizontal axis therefore I question your lift theory. Also I have never seen an airfoil that resembles a SWC profile. Where does it get its lift? My little Marlin wants to know. Zero your long range rifle at 3' high at 100yds and don't shoot at any thing over 250 yds and you won't have to worry about where to hold. If you want to worry, determine the horizontal distance, not the line of sight, to your game and that is what your hold should be based on. If you are going on a cable TV show and shoot game at 800-1000 yds you will want to worry about shooting uphill or down and But this should not be a problem for you because you have been shooting at long distances targets every week for the last 10 years and know just how your load in your rifle will preform. We mortals keep our shots under 250yds. Less if it is not the last hour of the last day of the season.

[303Guy]

Was that meant to be sarcastic? I hope not. I only have 303's, most of them old - like over a 100 years old.

All I said was a bullet fired horizontally does not fall to the ground at the same rate as one being dropped as was taught in high school (not far of though). I was challenged on my statement that bullets 'fly' and I was trying to explain, is all. I produced a number of quotes but I didn't claim to be an expert shot or long range target shooter. I did say it's not overly relevant to the thread but I'll attempt to answer the question;

It's a phenomena called the Magnus effect. Basically it's a 'lift' generated by a rotating cylinder or ball or spitzer bullet when air passes over it. A sailing craft was once fitted with a pair of cylinders rotated by a motor and it actually sailed in a wind but the idea was not too successful. To have any lift at all, a boolit/bullet has to have yaw and that's what this is all about. A bullet/boolit will have yaw as gravity induces a trajectory. It's called Yaw of Repose. That was part of what I was trying to prove.

80175

This is for a bullet travelling through a crosswind. It's not a very strong lift and only really shows up at long range or in strong winds close to the muzzle. It can be a significant factor and seems to increase at lower BC. I've had wind drift issues at 100m, like a bullet drifting right off an A4 target sheet onto the next.

[Larry Gibson]

Hmmm. .......seems we are understanding now that bullet drift, wind drift and lift are all different aspects of a bhai ullets flight.

Larry Gibson

BTW; the reference 303 uses is correct. I suggested Rinker as his book is an easier read and not so easy to misunderstand.

[felix]

Yep, 303guy just illuminated what pro breaking ball pitchers inherently "knew" all the time. Good pitching coaches employed relief pitchers based upon wind direction and the pitchers' ability to rotate the ball accordingly for a hellatious curve or slider depending on the hitter. ... felix

[Duckiller]

303, No scarsam intended. Most of my guns are older and great for hunting , but not benchrest accurate. With a 2-3 MOA gun I am not sure if I could see a boolit "Fly". I worry about gravity, horizontal distance to target and cross winds.

[303Guy]

Well, it now seems wind drift is more significant than I had realized. I'm not good at estimating hold over or under so I sight my rifles to have a point blanc rise and fall of 1¾" from the line of sight and with a 2" high scope that gives me 200yds point blanc range with my hornet and 180 yds with my j-word 303. For cast I expect no more than 150yds. I don't expect to shoot cast at too much elevation but I see at 30 degrees which is possible, I will have to keep elevation in mind. And wind. Winds can be strong in the hills! Elevation could be significant with longer range shooting with my 25-303 so I better get out there and start practising and learning how to allow for it.

PS. All my guns are older than I am! I have to use my great nephew's picture for my avatar because the system won't allow mine - it gives a 'driver out of date' error message!:wink:

Nah, I'm only 60.