Uphill/downhill.

basil

Distinguished Member
I`m not trying to purposely make myself sound thick here but..............
Does a bullet fired uphill lose its velocity quicker than a bullet fired downhill??
basil.
 

basil

Distinguished Member
300wsm said:
Yes

fired at 90 deg to the earths surface

Up bullet being slowed by gravity

Down bullet accelerated by gravity
Maybe i should have worded my question better, i was meaning, say over 200-300 yards at a 45 degree angle. Though i`m guessing the answer is the same.
basil.
 

snowstorm

Well-Known Member
IIRC from school, an object moving through space is an object moving through space, irrespective of the angel to the body in question, so gravity will have the same pull on that moving object whether its angled up or down. Gravity doesnt have less pull at any given second at steeper angles.

It would pull the object further down by the time it reaches 100 yards than it would a flat shot, because the round is in the air longer to get there(pythagoras).

The downward angled shot will hit the ground sooner but it will have dropped by the same amount and travelled the same distance as the upward shot when it does.

Having said that there will in theory be a tiny miniscule unmeasurable difference due to the fact that the upward round will be slightly further away from the body doing the pulling (the planet), but we are talking millionths of a m.m.

Try it for real - aim 6 inches high at 150 yds, then 6 inches low. You will have the same degree of drop.
 

tartinjock

Distinguished Member
Your shot placement will also be different. The Round/Bullet/Head, whatever you call it is not travelling as far.

ie, A bullet travelling at an angle, will cover a shorter distance uphill than that of one travelling parallel to the ground. There for gravity will have a lesser affect as it's NOT pulling down on the round for a true horozontal distance..

If you are unsure what I mean, draw a triangle, (With a right angle)measure up or down the angled line say 4cm, draw a line straight down to the Horizontle and then measure, it will be shorter uphill or longer downhill.

Hope that helps towards the answer you need.

TJ
 

snowstorm

Well-Known Member
I'm getting over complicated as well.

Simplifed - every second it goes away from you gravity will pull it down an inch from its path if there were no gravity at all (or whatever). It will pull the same degree whether its going up down or straight.

The bullets mass does not change and gravity pulls on mass. A bullet at a moment in time has a downward pull on it. How it got there or where its going next isnt relevant.

There - thats me trying to be less complicated!
 

snowstorm

Well-Known Member
308 150gn sierra Mk @ 2900fps shot at 0 elevation drops 12.59" at 300yds
308 150gn sierra MK @ 2900fps shot @ 30 degrees drops 9.64 @ 300yds.

Plus the initial distance higher or lower it was aimed at. So the 2nd one still drops more because it is in the air longer. They are both affected by gravity to the same extent.

30 degrees up and 30 degrees down will both drop by 9.64.
 

wadashot

Account Suspended
I was always lead to believe that if you were shooting at a deer, or anything else for that matter downhill at about 45 degrees you would need to shoot for the top of the shoulder as against the heart, as gravity pulls down on the bullet, (common sense would tell you this) :rolleyes: but when you shoot at the same deer at 45 degrees uphill you would say shoot at nearer the bottom of the heart, as the bullet would rise :rolleyes: Although the amount of movement in the bullet, up or down would be neglegible, which has been mentioned. :rolleyes:

Sorry if this repeats anything that has already been said but feel it is a better way of understanding it :eek:

wadas
 

Andy L

Well-Known Member
Snowstorm, You are confusing the hell out of me! :lol:
When you are shooting up hill at a target that is 300 yds away, you should treat the target as if were less than this distance (say 250m depending on angle) This is because gravity only affects the horizontal distance. A 300yd horizontal shot always drop more than a 300 yd angled shot. Hope this makes sense and I am sure I am right but then, my wife says I always think that! ;)
 

jingzy

Account Suspended
MMM

I believe that a shot fired horizontally has more gravitational pull on it than one fired at an angle away from horizontal.

To shoot up or downhill, the aim should be low as there is less gravitational pull on the projectile as it is away from the horizontal to the earths core.
 

snowstorm

Well-Known Member
Remember there no such thing as a sraight or horizontal shot - even aiming dead ahead the bullet always follows a curved trajectory - so even a 'horizontal' shot is fired up hill.

Also, gravity works on an object independently of its angle to the vertical. That's the key point - it exerts the same pull at an instnt in time.

It's do with product moment energy - are there no physicists on here who can explain it less clumsily than I?! :)
 

Bandit Country

Well-Known Member
I'm not a physicist, but here goes.....Think of the right angle triangle with the short side vertical and the hypotheneuse (the diagnonal line) running down from the top of the short side to the acute angle with the third side - call that side the base line and the the firer is at the acute angle. The distance along the base line to the target (the vertical right angled side) is say 300ms. Measure the same distance - 300ms - along the hypotheneuse (diagonal, 'uphill') line and it wont get to the angle with the vertical side, because as we all know the hypotheneuse is the longest side of a right angled triangle. However if you draw a vertical line down from the 300m point on the hypotheneuse it will reach the baseline short of the 300m horizontal distance. So although both rounds will have travelled 300ms in space the round fired along the hypotheneuse (uphill) has travelled a shorter horizontal distance and is less effected by gravity in that gravity acts at right angles to the horizontal - in this case the baseline or Earth's surface. Crudely speaking it will have been 'pulled down' less by gravity than the round fired along the baseline to 300ms. As a result, because the hypotheneuse round has been 'pulled down' less it will strike the target high. The same physics are true for downhill shots - you are simply shooting down the hypotheneuse as opposed to up it. If shooting up or downhill you should always aim lower or adjust your sights accordingly. If in doubt get out on a nice big open hill, put out some targets and give it a go. Top tip ... tracer saves a lot of walking! :) Top tip II ... watch the backstop!
 

mack

Well-Known Member
angle

At the distances we SHOULD be shooting at it makes so little difference as not to matter.
 

Bandit Country

Well-Known Member
Couldn't agree more Mack - although this is the Ballistics & Technical thread so I'm assuming the ethics of practical stalking or deer management aren't under debate.
 

jingzy

Account Suspended
http://www.loadammo.com/Topics/April04.htm

Look at the link above and you will even get drawings.

Shooting Uphill and Downhill

Shooters are sometimes confused about the bullets path when shooting uphill or downhill. For instance, does the bullet strike high when shooting downhill and strike low when shooting uphill? Sierra and other bullet companies have done extensive testing on shooting uphill and downhill and have found the following to be true for a given cartridge:

The true vertical bullet drop is the same for level fire and uphill or downhill shooting for the same range. See Figure 1. The vertical drop, do, is the same for all three methods of shooting over the same range.
The bullet velocity is the same whether shooting over a level range or shooting uphill or downhill. In other words the bullet does not slow down faster in uphill shooting than with level shooting and the bullet velocity does not increase when shooting downhill.
A rifle zeroed in at level range will shoot higher when shooting uphill or downhill.
For a given angle of fire the bullet will shoot high by the same amount weather shooting uphill or down hill.


Fig 1- Bullet trajectories for level fire, shooting uphill, and shooting downhill

The theory as to why the bullet always shoots high for uphill and downhill shooting is based on the projectiles path in relation to the pull of gravity. Gravity works perpendicular to the horizontal line. It's the horizontal distance traveled by the bullet that is important rather than the actual linear distance traveled. This is explained by the use of trigonometry and the right triangle shown in Fig. 2.


Fig. 2-Using trigonometry to explain uphill/downhill shooting

According to the rules of trigonometry the cosine of THETA is equal to the horizontal range divided by the slant range (hypotenuse). By rearranging the terms, the horizontal range is equal to the slant range (hypotenuse) multiplied by the Cosine of THETA.

Assume we have zeroed a rifle at 300 yd on a level range and we are shooting at a target on a slant range of 300 yards. Assume the slope angle THETA is 30 degrees. The cosine of 30 degrees is 0.87. The horizontal range for the bullet is only 261 yards (300 * 0.87). In order to hit the target we should hold the gun as if the target were only 261 yards away not 300 yards. If we shoot where the scope crosshairs intersect the target we will shoot over the target. In the field, you probably don't really know the slant range or the slant angle very accurately. Just remember to always aim lower, because any slant range shot, either downhill or uphill, will be higher than if it were a horizontal shot.

 

tartinjock

Distinguished Member
jingzy said:
http://www.loadammo.com/Topics/April04.htm

Look at the link above and you will even get drawings.

Shooting Uphill and Downhill

Shooters are sometimes confused about the bullets path when shooting uphill or downhill. For instance, does the bullet strike high when shooting downhill and strike low when shooting uphill? Sierra and other bullet companies have done extensive testing on shooting uphill and downhill and have found the following to be true for a given cartridge:

The true vertical bullet drop is the same for level fire and uphill or downhill shooting for the same range. See Figure 1. The vertical drop, do, is the same for all three methods of shooting over the same range.
The bullet velocity is the same whether shooting over a level range or shooting uphill or downhill. In other words the bullet does not slow down faster in uphill shooting than with level shooting and the bullet velocity does not increase when shooting downhill.
A rifle zeroed in at level range will shoot higher when shooting uphill or downhill.
For a given angle of fire the bullet will shoot high by the same amount weather shooting uphill or down hill.


Fig 1- Bullet trajectories for level fire, shooting uphill, and shooting downhill

The theory as to why the bullet always shoots high for uphill and downhill shooting is based on the projectiles path in relation to the pull of gravity. Gravity works perpendicular to the horizontal line. It's the horizontal distance traveled by the bullet that is important rather than the actual linear distance traveled. This is explained by the use of trigonometry and the right triangle shown in Fig. 2.


Fig. 2-Using trigonometry to explain uphill/downhill shooting

According to the rules of trigonometry the cosine of THETA is equal to the horizontal range divided by the slant range (hypotenuse). By rearranging the terms, the horizontal range is equal to the slant range (hypotenuse) multiplied by the Cosine of THETA.

Assume we have zeroed a rifle at 300 yd on a level range and we are shooting at a target on a slant range of 300 yards. Assume the slope angle THETA is 30 degrees. The cosine of 30 degrees is 0.87. The horizontal range for the bullet is only 261 yards (300 * 0.87). In order to hit the target we should hold the gun as if the target were only 261 yards away not 300 yards. If we shoot where the scope crosshairs intersect the target we will shoot over the target. In the field, you probably don't really know the slant range or the slant angle very accurately. Just remember to always aim lower, because any slant range shot, either downhill or uphill, will be higher than if it were a horizontal shot.


Was what I said?? ;)

Well done for finding the info, been head scratching this today with a couple of others.

TJ
 

mack

Well-Known Member
reply

Bandit Country said:
Couldn't agree more Mack - although this is the Ballistics & Technical thread so I'm assuming the ethics of practical stalking or deer management aren't under debate.
Point well taken.
 

basil

Distinguished Member
I had a feeling this would be a lively discussion.
Sorry guys, but i had to ask.
basil.
 

Bandit Country

Well-Known Member
jingzy said:
http://www.loadammo.com/Topics/April04.htm

Look at the link above and you will even get drawings.
Thanks for the link Jingzy. I've been asked this before and the pics make it pretty clear. I didn't realise that our American cousins also spell "Hypotheneuse" differently to us!
 

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