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Author Topic: Shooting at deer downhill question  (Read 4032 times)

Offline Stein

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Re: Shooting at deer downhill question
« Reply #15 on: May 10, 2017, 08:41:07 AM »
Its not that complicated - on phone calculator press type incline in degrees, press "cos" button, times yards.  Done.

Even easier, press the single button on my Vortex rangefinder.

Offline yakimanoob

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Re: Shooting at deer downhill question
« Reply #16 on: May 10, 2017, 09:56:33 AM »
Its not that complicated - on phone calculator press type incline in degrees, press "cos" button, times yards.  Done.
This would give you the vertical distance, in yards, between your target and a projected horizontal line from your position.  Why would you want to know that value in a shooting situation?

Offline yakimanoob

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Re: Shooting at deer downhill question
« Reply #17 on: May 10, 2017, 09:59:03 AM »
Even easier, press the single button on my Vortex rangefinder.
:yeah:

Modern rangefinders are wondeful.

Offline Magnum_Willys

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Re: Shooting at deer downhill question
« Reply #18 on: May 10, 2017, 10:31:31 AM »
Its not that complicated - on phone calculator press type incline in degrees, press "cos" button, times yards.  Done.
This would give you the vertical distance, in yards, between your target and a projected horizontal line from your position.  Why would you want to know that value in a shooting situation?

Sohcahtoa........    sin would give you vertical

Offline yakimanoob

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Re: Shooting at deer downhill question
« Reply #19 on: May 10, 2017, 04:16:12 PM »
Its not that complicated - on phone calculator press type incline in degrees, press "cos" button, times yards.  Done.
This would give you the vertical distance, in yards, between your target and a projected horizontal line from your position.  Why would you want to know that value in a shooting situation?

Sohcahtoa........    sin would give you vertical

True.  My mistake.  Same question though -- why would you want to know the distance of the horizontal line from you to the vertical line extending up from the deer?   

Offline Nash

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Re: Shooting at deer downhill question
« Reply #20 on: May 11, 2017, 07:59:16 AM »
Listen to The Hunt Backcountry podcast, episodes 72 and 73. Great shooting info and your question is discussed at length.

Offline Magnum_Willys

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Re: Shooting at deer downhill question
« Reply #21 on: May 11, 2017, 08:17:01 AM »
Its not that complicated - on phone calculator press type incline in degrees, press "cos" button, times yards.  Done.
This would give you the vertical distance, in yards, between your target and a projected horizontal line from your position.  Why would you want to know that value in a shooting situation?

Sohcahtoa........    sin would give you vertical

True.  My mistake.  Same question though -- why would you want to know the distance of the horizontal line from you to the vertical line extending up from the deer?

Your bullet drop is based on the horizontal range not the line of sight range - aka "True Ballistic Range" .     Your angle compensating rangefinder in its most basic design measures the line of sight distance, the angle and multiplies the cos of that angle times the line of sight distance to display your the horizontal distance.   

Offline jmscon

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Re: Shooting at deer downhill question
« Reply #22 on: May 11, 2017, 08:44:13 AM »
Gravity affects the horizontal distance, not so much the line of site. Air resistance is more constant and, if shooting down a veriticle face, would slow the bullet down to its terminal velocity. It would take a long, long distance but it would happen. Gravity affects the trajectory but air resistance is what slows the bullet down and will bring it sub sonic eventually. Gravity won't speed the bullet up, air resistance is too great.

Like some are saying, don't worry about it too much. Like bob33 said 45* slope and 200 yards line of site equate to 141 yards horizontal. That's how your bullet will be drop will act.
My interpretation of the rules are open to interpretation.
Once I thought I was wrong but I was mistaken.

Offline yakimanoob

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Re: Shooting at deer downhill question
« Reply #23 on: May 11, 2017, 11:17:18 AM »
AJ, we're veering off topic here, as we're all in agreement that at your stated range of up to around 200yds, you're better off ignoring the effect of the angle.  So if you or a mod want us to shut up, I'll gladly do so.  But until I'm told...   :chuckle:

Magnum_Willys, Jmscon, thinking in terms of the horizontal distance is incorrect, and will lead to some pretty significant error at longer ranges.  For example, say you are shooting at 500yds (along line of sight) at 30 degrees down.  In this case, the force of gravity pulling the bullet down (or more specifically, perpendicular to the LOS) is m*g*cos(30), but there is also a component of gravity pulling the bullet along the line of sight equal to m*g*sin(30).  IF the bullet were traveling in a vacuum, then this would give you the same change in drop (i.e., the difference between the drops shooting at 500yds horizontal and 433yds (500yds*cos30) horizontal would be the same difference in drop between 500yds horizontal and 500yds shooting down 30 degrees).  This change in drop, according to shooterscalculator.com and assuming the previous values of .507 BC, 180gr bullet, and 2750fps muzzle velocity, is 17.56 inches.  Meaning the bullet drops 17.56 inches less at 433yds than it does at 500yds.  In a vacuum, shooting down at 30 degrees would also cause a 17.56" reduction in drop, but because of the component of gravity pulling along the line of sight, the bullet would accelerate and arrive sooner. 

But as jmscon pointed out, we don't shoot in a vacuum (and you're 100% correct jmscon in saying the bullet wouldn't speed up -- the drag force dramatically overwhelms the small component force of gravity pulling along the LOS).  But there is still a force pulling on the bullet along the LOS towards the target equal to m*g*sin(30), which reduces flight time.  Running the ballistics computer with the same inputs as above but assuming a 30 degree down angle, we find the drop to be 45.10" at 500yds (compared to 55.10" at 500yds shooting horizontal, so the bullet drops a clean 10" less than it would have if shooting horizontal).

Long story short, if you were shooting at 500 yds down at 30 degrees, and you simply multiply your distance by cos(30) and shoot like you were shooting at 433yds horizontal, you'll be 7.56" low.  That's a pretty sizeable error and could easily lead to a missed or wounded animal.   

Offline jmscon

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Re: Shooting at deer downhill question
« Reply #24 on: May 11, 2017, 12:27:30 PM »
Here is good article: http://www.rifleshootermag.com/network-topics/tips-tactics-network/hitting-a-high-or-low-angle-shot/

Gravity is acting pirpendicular to horizontal not line of sight.

My interpretation of the rules are open to interpretation.
Once I thought I was wrong but I was mistaken.

Offline Igor

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Re: Shooting at deer downhill question
« Reply #25 on: May 11, 2017, 05:20:17 PM »
molṑn labé

Offline yakimanoob

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Re: Shooting at deer downhill question
« Reply #26 on: May 11, 2017, 09:47:40 PM »
Here is good article: http://www.rifleshootermag.com/network-topics/tips-tactics-network/hitting-a-high-or-low-angle-shot/

Gravity is acting pirpendicular to horizontal not line of sight.

Certainly, yes, gravity always acts towards the center of the earth. When we talk about bullet "drop" when shooting at an angle, A, we're speaking in reference to the line of sight, so to figure out that drop in relation to line of sight, we have to consider how gravity is acting in relation to line of sight.

So we split the force of gravity into its component vectors, with one component equal to m*g*cos(A) acting perpendicular to the line of sight, and the other component equal to m*g*sin(A) acting along the line of sight. These two component vectors sum to equal the total force of gravity equal to  m*g acting perpendicular to horizontal as you stated.

The technique magnum_willys (and the article you posted) described only accounts for the first component that acts perpendicular to the line of sight and ignores the second vector acting along the line of sight. It also ignores the air dynamics, leading to error.

P.S., I'm simplifying by talking about line of sight. In reality these calculations are affected by the difference between line of departure (or bore line) and line of sight, especially at extreme angles or extreme distances.

P.P.S., I find it a little funny that the article dismisses velocity as having little effect on bullet flight. Tell that to everyone obsessing about muzzle velocity and talking about magnum cartridges as "flat shooting" because of all that powder.

Offline scoutdog346

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Re: Shooting at deer downhill question
« Reply #27 on: June 01, 2017, 07:17:17 PM »
What caliber?  Scope?  You may want to consider a 200 yard zero.  What distances do you think you will be shooting?

http://www.chuckhawks.com/shooting_uphill.htm

Do a search on sighting in.  Lots of info out there.

A range finder that shows true ballistic range in very helpful.

Most important practice a lot!


Tikka t3x 30-06 with a leupold vx2 4-12 50mm. I am for sure going to get myself a range finder this season. From the area I'm scouting I could easily get a 150-200 yard shot. I can't see myself getting very close to the deer like within 100 yards. I will also be looking down hill into some clear cuts so maybe 150-200 yard downhill shots. I'm using 180 grain bullets. I can't seem to find a place to sight my gun in at 200 yards. All the legal target shooting areas are 100 yards or less. I'll have to see if any local ranges have 200 yards
with that gun...if u r dead on at 100 yard shot and the buck in under 250 yards don't shoot high or low just right on. don't make things any more confusing then need be as urban normal shaking will cancel things out.  think about the longest shot u think ur going to take and figure out what u got to do then and repeat it to ur self intermittently as ur hunting or write it down on so thing u can see as ur hunting and make sure u can see it with minimal movment. but yeah man...250 or under just put the cross hares right where u want to hit.

 

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