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Long Range Tricks And Toys By Ian McMurchy

 
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  #8  
Old 01-26-2008, 10:51 AM
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Join Date: Sep 2007
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Angled shots

Ian,

In this excellent article you state:

“Bottom line is that angled shots are NOT as far as they might appear, the bullet does not travel as far horizontally so it is not effected by gravity as long as it might seem.”

Ok, here’s where I struggle. In an extreme example, I am on a canyon rim. 300 yards below me and 300 yards away (horizontally), is my trophy. The distance from the canyon rim to the target is 424 yards, the angle is 45º.
My rifle is zeroed at 300 yards. The difference between the horizontal distance and target distance is 142 yards.
For arguments sake, my bullet is traveling at 3,000 ft/sec. At this speed, the bullet should be in the air .142 seconds longer than if the target were at 300 yds horizontally. Yes?
The bullet is in flight longer, thus affected by deceleration, friction with air molecules and gravity longer yet it will hit the target high if I don’t correct for the angle.
My math may be flawed but this is counterintuitive.
Gravity is not just a suggestion, it’s the law, I don’t dispute it, I just don’t understand its effect on angled shots.

Aitch
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  #9  
Old 01-26-2008, 03:18 PM
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Join Date: May 2001
Location: Sask. Canada
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The way I have had it explained to me is this is all about gravity, and gravity pulls straight down on things. Therefore the horizontal distance, the bottom line of a right triangle, is the distance over which gravity can pull down. We shot from a three story tower once at 300 yards and the difference was about diddly, maybe a "tich" of hold-under but not much. I hope to play with this someday, I know the perfect place just have to make the time to do it.
I believe the distances would have to be very long and the angle very significant for this to become a factor. But that is what some of the guys here shoot in. The ACI was developed for a reason. You are correct, gravity is the primary factor, we just have to accept it only pulls straight down, not on the hypotenuse distance.

Last edited by Ian M; 01-26-2008 at 03:23 PM.
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  #10  
Old 01-26-2008, 07:45 PM
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I find acceptance of things unexplainable as in "we just have to accept" less than satisfying. I felt the same way when Monsignor Nolan told me "it's a matter of faith".
If gravity only effects the bullet over the horizontal distance "the distance over which gravity can pull down" why wouldn't the point of impact be the same?
I hope someone can direct me to an explanation of this phenomenon. Why is gravity less above or below horizontal? Is it the same if you are shooting up or downhill?
"Gravity for Dummies" perhaps. There is also the distinct possibility that I would just not understand an explanation.
I thank you for your time and expertise.
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  #11  
Old 01-27-2008, 12:47 AM
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aitch,
To be honest with you I have never given angle shooting much thought, other than what I heard from instructors on shooting courses and what I saw the time we shot at an angle at 300 yards and essentially nothing much happened. I guess you could say I blindly believed what they told me, but I certainly should not have expected others to. You have a much more inquisitive mind.

Hopefully some guys who are into exterior ballistics can explain this better, I look forward to learning more myself.

I always think of myself on a cliff, the critter way below on the next mountain. My bullet would be the hypotenuse of the right triangle, but the real distance is the base of the right triangle. Now I believe you are correct about the varying time of flight for the distance the bullet travels. We say wind drift is directly related to time of flight. Why is not drop, damned if I can say. How in heck that works for shooting uphill, again I just believed what I was told. Sorry about not having a better answer, maybe I can get one from my industry contacts or from the many sharp guys on this forum. That is why I hang out here, to learn.

Perhaps I could get Ward Bryan, the owner of Sniper Tools and maker of the ACI to chime-in. I will send him a note tonight.
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  #12  
Old 01-27-2008, 02:58 AM
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Join Date: Jan 2008
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My grandfather and father taught me from an early age that gravity pulls straight down toward the center of the earth, if I shoot straight up the bullet will not have any drop. gravity can only pull the bullet straight down so if you shoot steep up or down the gravity your bullet fights is the same if you were shooting to any target on vertical plane. Basically if you built a huge vertical wall that and hung targets at all different heights and angles from you, the drop would always be the same.

Here's the way Wayne van Zwoll explains it, "If you shoot horizontally, gravity acts perpendicular to the bullet path and thus has a pronounced effect on it. Gravity pushing down on the shank of a bullet is the equivalent of a strong full-value or right-angle wind. If the wind shifts to quarter toward or away from a bullet, it drifts less. Apply that principle to bullets fired at uphill or downhill angles, and you would expect less drop as gravity is forced to act obliquely. Think of a bullet fired straight up or straight down. In the absence of wind, neither would scribe an arc. The tug of gravity would be parallel to the line of the bore, so there'd be no reason for the bullet to deviate from a straight path. A bullet fired straight up would travel until gravity and drag pulled it to a stop; then it would decend. The earth's spin would prevent the bullet from landing where it was launched, but touchdown would be very close to that spot....
At any shot angle between horizontal and vertical gives you flatter trajectory than if you'd fired horizontally, wether you're shooting up or down. The effect of gravity on bullet speed- its pressure on noce or tail- is negligible. So you can hold the same, wether shooting up or down. But that hold will differ, especially at long range, from the hold you would want for a horizontal shot. Simply put, you want to aim as if the shot distance were the same as the horizontal component of the shot."
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  #13  
Old 01-27-2008, 12:17 PM
WWB WWB is offline
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Angle Shooting

Everything always goes back to the basics... And the Basics for me takes me back to an incident that happened in Texas during the 1970's. It wasn't a hunting experience, but a defensive survival one. I was not there, however the incident is a Testimony regarding the importance of correcting the sloped distance to target, to the corrected for gravity distance.

There was a bad guy on top of a building shooting down at everyone he could with the intent of killing them. Many innocent people were killed and it took a multitude of armed Citizens to finally stop the murdering.

In this particular scenario, picture yourself in the defensive posture. You are armed with a Remington 700 chambered for the .308 Win. You are 300 yards out, aiming and shooting up to the top of a sixteen story building on a 45 degree angle. If you do not correct your sloped distance to target to the corrected for gravity distance, your bullet will be eight inches above your point of aim. Since you can only see approximately sixteen inches of your target, the correction is mandated and absolutely necessary.

When you Zero your rifle you usually do it shooting straight out, flat. The full force of gravity is indeed bearing down on the projectile. In this zeroing situation, you will adjust the sight's height above the bore for this particular constant; "that being the full force of gravity."

However, when you begin to aim up or down on an angle, the force of the gravity depreciates and the "Constant" (full force of gravity) changes, (lessens). But the sight height above the bore that you dialed in while zeroing, has remained the same.

There are several other elements that should be addressed in order to correct for the change of the "Constant" (force of gravity) and the way that I can explain this best to go through the three methods of correction.

The original method is called the Rifleman Method, and it is merely multiplying the cosine number of the angle that you are holding on to the sloped distance to target. You are all probably familiar with this as your objective is to figure out the "Flat" or straight line distance to target. Because you zeroed your rifle on a flat plane, right? So, 300 yards multiplied to the cosine number for 45 degrees (.7) equals 210 yards. 300yds X .7 = 210.

The next and more accurate method is to utilize the "Improved Rifleman" method. That is where you multiply the cosine number to your "hold" as depicted on your data card. For example, I shoot a .300 Win Mag; and my hold for a 600 yard target without aiming on an angle, is 11.25 MOA. If I was aiming on a 30 degree angle, my cosine number would be, ".87." In this case, I would then multiply the cosine number for 30 degrees, which is .87, to my MOA hold of 11.25. 11.25 X .87 = 9.78 MOA and this is what I would dial into my scope, or if I had a reticle that subtended in Minute of Angle, I would hold on the corresponding mark.

The most accurate method is to utilize Ballistic Targeting Software such as the one manufactured and distributed by "Night Force." This is because the software includes in its calculation, the bullet's weight, the Ballistic Coefficient of the particular bullet that you are utilizing, the sight height above the above, the muzzle velocity and the site in distance. With these set of elements, in addition to the software’s trajectory validation sub-routine, it is capable of calculating the bullets own unique deceleration curve, and deliver to you, The Shooter, a very precise hold.

With the Night force Ballistic Targeting Software, it utilizes either the Cosine number of the angle or just the angle. Many Hunters appreciate utilizing the "angle" that they are holding on because they can use Night Force's Software on their desktop computer to create a data card with the angles that you might be holding on as a cross reference chart in the field. As an example, if you are aiming at a deer 500 yards out, and you are holding on a 20 degree angle, you look at the distance to target on the left hand side of your card, then look at the angle that you are holding on along the top of your card and you will be able to locate your hold for the shot. This is very fast and eliminates the need for an additional calculation in the field...

The following link depicts Sniper Tools Angle Cosine Indicator. Once attached to your rifle, that is where it will stay.

aci-htm Sniper Tools
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http;//www.snipertools.com

Last edited by WWB; 01-28-2008 at 04:58 PM. Reason: Posting a Picture of the ACI
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  #14  
Old 01-28-2008, 04:07 PM
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Join Date: Oct 2007
Location: Windsor Colorado
Posts: 46
One more answer from the boys over at Ovis.

Grand Slam Club / Ovis :: Uphill Shooting, by Zack Skochko

The 308 gif image might not open if you have pop ups turned off.
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