[Jim K]

I understand better where you are coming from, calculating b from c cos (35 degrees). That works fine and does give you the length of line b (the calculation assumes the angle ba is a right angle). But your basic falacy is in believing that the bullet is "affected by gravity" only for the horizontal distance b. That is simply not true, depending in part on the velocity and caliber. The bullet is affected by gravity (falling) at every point on its path between the muzzle of the hunter's rifle and the deer. And that path is a parabolic curve, which means it is longer than either b or c. To see this, draw a curve upward from the line of sight (a plain arc will do for illustrative purposes). Now measure ALONG THAT CURVE. That is the length of the bullet's path and the distance (and time) for which the bullet is "affected by gravity." And your calculations based on straight lines go out the window.

Now let me be clear. I am not saying there is no need to aim high/low in cases where there is a vertical distance between shooter and target. I think if you draw a true parabolic curve on a strip of paper, pin it at the shooter and swing it around, you will be able to see what happens, not exactly, but close enough.

What I am saying that your method of calculating the amount of holdover/holdunder is not valid. Can it be an approximation? That depends on the length of the bullet's path, which depends on its trajectory - a .45-70 will have a longer path (sharper curve) than a .30-'06. And of course its velocity, which you consider a constant, will be dropping all the time. All those things have been calculated by smarter folks than I, but your method is simply not valid.

Jim

 

[sting75ray]

I am just glad it is flat out here in western Ok and don't have to worry about all of the angles while shooting my 45/70 downrange. Great info though. I remember reading something along those lines in a Shooting Times magazine a few years back.

 

[goofy]

Jim K sory The Numbers that JLA is saying IS corect I spent 4 hours with a cornell profesor last night talking about it.The bullet is efected by gravety the second it leaves the barrel WE MAKE IT ARCH if we don't it will hit the ground quick. So we adjust our scopes so it will not.The round arches because we are shooting it up in the air and setting our scopes so that it hits the target.When a projectile is lunched it immediately starts to drop WE create the arch so it can go farther.And gravity effects it differantly shooting up and down.When shooting up gravity pulls it back(slowing it down)and when shooting down it slows down slower(keeping a more constent speed).The arches that are created are different.The arch when shooting up is greater then shooting down.This is due to the diference of the track due to the effects of gravity. Gravity remains constent at the same angle wether you are shooting up,down,leavel. It pulls straight to the center of the earth.Now there are ALOT of variables weight of the projectile,speed,humidity,wind and angle.But the numbers that JLA gave are corect(simplifyed) but correct.And this goes for ANY projectile bullet,arrow,rocket,bottle,stone it does not matter.

 

[JLA]

And to add, once you figure the holdover and adjust your scope for THAT range, you have just set the arc required for the round you are shooting at the holdover distance..

Bullets travel too fast to take into account the distance being up or down hill, they only meet atmospheric resistence and gravity, one of which is constant and the other of which relates directly to the bullets Ballsitic co-efficient of the bullet.

 

[JLA]

I understand better where you are coming from, calculating b from c cos (35 degrees). That works fine and does give you the length of line b (the calculation assumes the angle ba is a right angle). But your basic falacy is in believing that the bullet is "affected by gravity" only for the horizontal distance b. That is simply not true, depending in part on the velocity and caliber. The bullet is affected by gravity (falling) at every point on its path between the muzzle of the hunter's rifle and the deer. And that path is a parabolic curve, which means it is longer than either b or c. To see this, draw a curve upward from the line of sight (a plain arc will do for illustrative purposes). Now measure ALONG THAT CURVE. That is the length of the bullet's path and the distance (and time) for which the bullet is "affected by gravity." And your calculations based on straight lines go out the window.

Now let me be clear. I am not saying there is no need to aim high/low in cases where there is a vertical distance between shooter and target. I think if you draw a true parabolic curve on a strip of paper, pin it at the shooter and swing it around, you will be able to see what happens, not exactly, but close enough.

What I am saying that your method of calculating the amount of holdover/holdunder is not valid. Can it be an approximation? That depends on the length of the bullet's path, which depends on its trajectory - a .45-70 will have a longer path (sharper curve) than a .30-'06. And of course its velocity, which you consider a constant, will be dropping all the time. All those things have been calculated by smarter folks than I, but your method is simply not valid.

Jim

IT ALWAYS WILL BE A RIGHT ANGLE. It can never not be.

 

[Jim K]

"Bullets travel too fast to take into account the distance being up or down hill..."

That is not quite true either, but I refuse to get in any deeper. And pardon me, but didn't you just negate your whole argument? You claimed to have found a precise number that will give a holdover distance, apparently without regard to velocity, bullet shape, air resistance or any of those other nasty little details. Now you say that they do count, which means your precise figure is still invalid.

Hi, Goofy,

Most of that is perfectly correct. But how does it jibe with JLA's contention that gravity only affects the bullet while it is travelling the distance of line b and not at any other point in its own (curved) path?

Jim

P.S. With that, I give up. That darned pig just won't sing.

JK

 

[goofy]

Hi Jim K Well on your last post about your question. I if you are saying that gravity efects the bullet in the whole arch of it's flight you are right. And if JLA is saying that gravity only efects the bullet for the distance of B he is also right.You both are saying the same thing.The bullet may travel a total distance of say 300 feet in a arch up and away(I did not write down JLA numbers) But only travels 200 feet across the earth then the bullet is effected by gravity for all of it's 300 foot arch(up and away) with in the 200 lateral feet traveled.If you were to draw stright lines up from line B that would represent gravity even thow the bullet travels 300 feet(and is effected by gravity the whole time) up and away. It is only traveling 200 lateral feet across the earth.(effected by gravity the whole time)So you are both right about that.

 

[cutter]

That Info is very useful!! Thanks very much! It made sense to me, it give the true shooting distance and thats all. You need to know what the bullet drop is for your specific rd. Thanks again.

 

[JLA]

That Info is very useful!! Thanks very much! It made sense to me, it give the true shooting distance and thats all. You need to know what the bullet drop is for your specific rd. Thanks again.

Excellent. Someone else that perfectly understands how to use this math.. :thumbsup:

 

[wyoredot]

I'm heading out to the fabled land 'o plenty dumdogs. My trusty .257 Rbts and I intend to do crowd control. I will apply these things I have lernt when I try the 250 and 300 yd shots. I think it will be a blast. For me anyway.

 

[JLA]

"Bullets travel too fast to take into account the distance being up or down hill..."

That is not quite true either, but I refuse to get in any deeper. And pardon me, but didn't you just negate your whole argument? You claimed to have found a precise number that will give a holdover distance, apparently without regard to velocity, bullet shape, air resistance or any of those other nasty little details. Now you say that they do count, which means your precise figure is still invalid.

Hi, Goofy,

Most of that is perfectly correct. But how does it jibe with JLA's contention that gravity only affects the bullet while it is travelling the distance of line b and not at any other point in its own (curved) path?

Jim

P.S. With that, I give up. That darned pig just won't sing.

JK

No I did not negate my whole argument.. And I did not find 'A' precise number, I simply put 2 and 2 together using things I learned 10 years ago in HS and found an easy to use chart full of precise numbers that help to calculate holdover distance quickly in the field.. Again, THIS TOPIC is for determining holdover when shooting over an angle.. You still have to have a range card put together for the weapon system you are using to shoot over the angle so you can adjust the optics to compensate for THE HOLDOVER DISTANCE... Again, multiplying the cos of the angle by the line of sight ONLY gives HOLDOVER which ONLY accounts for the linear distance the bullet is affected by gravity, NOT gravity itself or any other variable... YOUR RIFLE/CARTRIDGES specific ballistics performance, which is a good idea to have on a range card taped to your weapon, calculates the rest of the variables just like shooting over a level distance. It seems pretty simple to me, and more and more folks chiming in seem to get it too. SO.. take it if you can use it, if you dont understand, feel free to disregard, I wish I could help you to understand because it really is useful information but apparently I am better at figuring out stuff like this while laying in bed at night than I am at explaining Trigonometry to a machinist..

 

[JLA]

I'm heading out to the fabled land 'o plenty dumdogs. My trusty .257 Rbts and I intend to do crowd control. I will apply these things I have lernt when I try the 250 and 300 yd shots. I think it will be a blast. For me anyway.

Please post a range report, some hands on application may help put the facts to rest..

Thanks Wyo..

 

[brad87]

I think what he's failing to understand is the fact that the parabolic curve of the bullets path through the atmosphere is already taken into account and is no longer an issue because you already sighted your rifle in at the range prior to taking it hunting.

When you can say that my rifle is sighted in for 200 yards, and I know at 250 I have 3 inches of drop, and at 300 I have 6 inches, etc. etc. etc... then once you find the distance using JLA's little math thing (btw, I HATED trig and geometry, I'll stick to algebra, thanks) your rifle will take care of the rest. The 300 yard line of sight thing he mentioned later on that came out to be a 261 yard equivalent shot, yeah, he just holds 3 inches high instead of 6 inches, because he knows how his gun shoots.

 

[JLA]

:thumbsup:

 

[The_Rifleman]

Nevermind, I am too busy to even think about all the false assumptions, but try this one. How does your system deal with the various trajectories for different ammunition?

Jim

I see what you mean JLA. His comment displays a total misunderstanding of the concept.

 

[Zane71464]

FINALLY......Found this thread Josh and thank you for your time and knowledge on this subject. The "avaerage" hunter-shooter" that Ive ever talked to in person never heard of such a thing. Not all, I stand corrected, but most and this was new to me as of just a couple years back when I believe it was you that got me into shooting the .22lr out to 300yds.
Well, Ive been digging for info and trying to figure this whole angle shooting out and pretty much have, sept, got a hugh problem with 'one" distance in particulair. I'll have to dig up a pic or two to decribe what I'm into.
It lasers 149 yards, but with my rifle trajectory, it's 250-300yds! I'll dig up a pic or two to better explain and with some help, might just get this long time headache of trying to figure this out understood!!! It's been bothering me for a couple years now. I'll dig up a pic er two....