Down hill shot question

[lionhunter]

I am hoping that one of you long range experts can answer this question. (Hypothetical of course) If you were lining up a shot from an elevated location, shooting down hill at aprox 120-130 degree angle and the deer was 380 yards where would you hold? I have always been told that at a major up or down hill to hold low, but how low? Is there a comp app that calculates down hill hold over?under? I have a cross hair that is dead on at 300 and one that is dead on at 400. If you had target turrets what would you dial it up for? any input would be helpful.

Whitey

[Coach]

I'm certainly no expert, but the math involved is fairly basic. The bullet will drop according to the horizontal distance between the muzzle and the target. So, whether you are shooting uphill or downhill the drop isn't determined by the actual line-of-sight distance to the target, but by the actual horizontal distance.

 

It's hard to tell in your exact situation how to do the math because you mention shooting downhill at 120-130 degrees. Keep in mind 90 degrees from horizontal would be straight down. I'm assuming you mean 120 - 130 degrees from straight up, which would put the downward angle at either 60 degrees down (180 - 120) or 50 degrees down (180 - 130).

 

In these cases, the horizontal distance would be 330 yards at 60 degrees and 290 yards at 50 degrees.

 

Here's a picture of this example using the 120 degree figure (actuall 60 degrees downhill).

 

Make sense?

[jeffro]

A 90 deg angle is straight down. You need to use an ACI. Angle cosine indicator. Take your range say 380yrds. Then take your dope for 380. Lets say its 5.0 MOA. Then use your ACI and get your reading. If it reads .80 then you take 5.0 times .80. Your dope would be 4.0 MOA. This is the advanced riflemans method. It doesnt make a huge dif until you get out there a ways as you see. .80 is quit steep if you get to messing around with the ACI.

[308Nut]

I am hoping that one of you long range experts can answer this question. (Hypothetical of course) If you were lining up a shot from an elevated location, shooting down hill at aprox 120-130 degree angle and the deer was 380 yards where would you hold? I have always been told that at a major up or down hill to hold low, but how low? Is there a comp app that calculates down hill hold over?under? I have a cross hair that is dead on at 300 and one that is dead on at 400. If you had target turrets what would you dial it up for? any input would be helpful.

Whitey

 

 

You have'nt supplied enough information to get the right answer. Air density, muzzle velocity, BC etc.... all plays a huge part in calculating an accurate number that you would use for compensation.

 

The illustration used by coach does and excellent job of showing you the principals of shooting at an angle.

 

The danger of using the riflemans method is that (due to trajectories) when the range increases and the angle steepens, the numbers are'nt right.

 

For example, using my 338 Edge in standard air density at 600 yards with a 30 degree angle the bullet drop is 39" as apposed to 53" shooting level. If I were to take the actual cosine value of .866 for 30 degrees and multiply it by 600 yards the answer is 519 yards. My bullet drop at 519 yards is about 32" which is 7" different than actual. Why is this? Because all of the variables were not included. If bullets were fired in a vacume, simply multiplying the distance by the cosine would work flawlessly. Then again, if we fired our rifles in a vacume, there would be no trajectory, only a straight line. When you add the trajectory factor into the equasion, each indavidual trajectory has to be compensated differently for.

 

The deeper the trajectory the worse it is as well.

 

For example, using my 308 in standard air density, the same scenario as above yields 61" level and 46" angled. Looking to 519 yards shows me 36". This is now an even larger error than the flatter shooting Edge.

 

The riflemans method will get you closer than nothing at all but to do it right you will have to employ a ballistic calculator for an accurate compensation or perform a very long equasion by hand. The numbers you need to do the math by hand are unfortunately also generated by a ballistic calculator.

 

It is also important to know that angles are angles. It doesnt matter if it is an uphill shot OR downhill shot the formulas and equasions are the same for both. If you deduct 12" for a downhill shot, you will also deduct 12" for an uphill shot for the same angle.

 

 

I hope that helps.

 

M

[jeffro]

308NUT is right about using a balistics calculator as the best means for finding the drop. The riflemans method is the cheap way to angle shooting as you wouldnt need to have a PDA.

[rclouse79]

Quote by 308nut

 

"Why is this? Because all of the variables were not included. If bullets were fired in a vacume, simply multiplying the distance by the cosine would work flawlessly. Then again, if we fired our rifles in a vacume, there would be no trajectory, only a straight line. When you add the trajectory factor into the equasion, each indavidual trajectory has to be compensated differently for."

 

I have gathered from your posts that you are a very good long range shooter. I do not question the fact that you know HOW things work, but your statement makes it apparent you do not understand WHY things work. A vaccum just means that there is no air resistance, and air resistance is NOT what causes things to fall. The reason a bullet falls is because the earth pulls the bullet downward due to the force of gravity. The only variables affecting the force of gravity are the mass of the earth, the mass of the bullet, and the distance from the bullet to the center of the earth.

If you shot a bullet in a vaccum its path would be different because the horizontal component of velocity would remain constant. If you shot a gun with a muzzle velocity of 3100 ft/s it would have a velocity of just over 3100 ft/s 1000 yds down range. This bullet would have dropped practically the same distance as a bullet shot with air resistance in the same amount of time. The only difference is it would be further downrange due to the fact it did not have rapid deceleration due to air resistance.

[azgutpile]

Quote by 308nut

 

"Why is this? Because all of the variables were not included. If bullets were fired in a vacume, simply multiplying the distance by the cosine would work flawlessly. Then again, if we fired our rifles in a vacume, there would be no trajectory, only a straight line. When you add the trajectory factor into the equasion, each indavidual trajectory has to be compensated differently for."

 

I have gathered from your posts that you are a very good long range shooter. I do not question the fact that you know HOW things work, but your statement makes it apparent you do not understand WHY things work. A vaccum just means that there is no air resistance, and air resistance is NOT what causes things to fall. The reason a bullet falls is because the earth pulls the bullet downward due to the force of gravity. The only variables affecting the force of gravity are the mass of the earth, the mass of the bullet, and the distance from the bullet to the center of the earth.

If you shot a bullet in a vaccum its path would be different because the horizontal component of velocity would remain constant. If you shot a gun with a muzzle velocity of 3100 ft/s it would have a velocity of just over 3100 ft/s 1000 yds down range. This bullet would have dropped practically the same distance as a bullet shot with air resistance in the same amount of time. The only difference is it would be further downrange due to the fact it did not have rapid deceleration due to air resistance.

 

I believe you both are saying the same thing.

[rclouse79]

"I believe you both are saying the same thing."

 

You are wrong. He is saying bullets drop due to air resistance. The fact is they drop due to gravity.

[Coues Sniper]

"I believe you both are saying the same thing."

 

You are wrong. He is saying bullets drop due to air resistance. The fact is they drop due to gravity.

Gonna go out on a limb here and say 308Nut is aware of gravity . I believe you are misunderstanding what he meant.

[rclouse79]

"Gonna go out on a limb here and say 308Nut is aware of gravity . I believe you are misunderstanding what he meant."

 

Everyone on earth is aware of gravity at some level. After all, everyone has seen its effects since they were born. There is a difference between being aware of something and having a sound understanding of how things work. You believe I misunderstood what he meant because you also do not have a basic understanding of physics.

 

308 QUOTE

"If bullets were fired in a vacume, simply multiplying the distance by the cosine would work flawlessly. Then again, if we fired our rifles in a vacume, there would be no trajectory, only a straight line."

 

Case #1- 308 was talking about a lack of air resistance when he referred to a vacuum. This is the correct definition of a vacuum. For those of you who agree with his statement and think objects follow a curved path because of air resistance, please explain why the moon follows a curved path the earth. (hint: there is no air resistance in space)

 

Case #2- When 308 referred to a vacuum he was thinking that meant no gravity. This is not the correct definition for a vacuum. In the case of no gravity the bullet actually would follow a straight line path. In this case there would be no need to multiply the distance by cos of the angle. In fact there would be no need to worry about distance at all. You would aim directly at the target regardless of distance.

 

The bottom line is it was a misconception. There is nothing to argue about, the laws of physics have been know for quite some time and not much has changed in the area of mechanics. Trying to defend the misconception simply announces your ignorance. Perhaps I should have not pointed it out. I am sure many people would have been happier thinking their bullets would follow a straight line path if they could get rid of that darn air resistance.

[Coues Sniper]

Please do not hint towards either me or 308 of being ignorant. If there is nothing to argue about, then calm down. If he misused the term "vacuum", then big whoopie. My point is, you're telling a guy who knows more than 99% of the shooters out there he is wrong and doesn't know that gravity causes a bullet to drop. It's ludicrous .

[Outdoor Writer]

Then again, if we fired our rifles in a vacume, there would be no trajectory, only a straight line. When you add the trajectory factor into the equasion, each indavidual trajectory has to be compensated differently for.

 

Hmmm, I'm not real good in calculating things, but the above is off according to the laws of physics. A vacuum still has gravity at work. Thus the bullet will still drop just as fast and as far as in the normal atmosphere. The only difference: it will travel farther before doing so.

[Outdoor Writer]

If you shot a bullet in a vaccum its path would be different because the horizontal component of velocity would remain constant. If you shot a gun with a muzzle velocity of 3100 ft/s it would have a velocity of just over 3100 ft/s 1000 yds down range. This bullet would have dropped practically the same distance as a bullet shot with air resistance in the same amount of time. The only difference is it would be further downrange due to the fact it did not have rapid deceleration due to air resistance.

 

 

Whoops. I should have read on and saw where you addressed it.

[rclouse79]

I am calm, I think this is fun. I said in my initial post that 308nut is probably a better long range shooter than most everyone, myself included. I know that I am ignorant in many areas, as is everyone else in the world. If I thought I knew something and someone pointed out that I had made a mistake I would be grateful. Thinking that you are an expert on physics based on the fact you know where a bullet will hit after punching data into a pda is ludicrous. If all you care about is where the bullet will hit and don't care about how it gets there then disregard my posts.

[Coues Sniper]

I don't think you understand what I am saying, so I'll try once more and leave it be . 308, along with most people on here, are fully aware of the physics involved and WHY the bullet does what it does. Not just the end result of a ballistics program. The error you are pointing out is, in my opinion, quite basic. I think you are nit-picking the use of a word and assuming a gross misunderstanding of fundamental physics was made. Which I believe is not the case. That is the reason for my comments.