Shooting on an angle

Dave King

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May 3, 2001
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2,366
I've been using the line-of-sight(LOS) distance and cosine of the angle to calculate 'corrected' target distance and it works fine. (I've been using Bruce N. Robinson's MilDot Master for a couple of years.) But, I recently read about using the cosine of the angle and applying it to the elevation correction. (Big discussion on Sniper Country recently.)

I was toying with my ballistics spreadsheet, one I share a common interest in with Peter Cronhelm, and can across a dilema.

I can get a 'corrected' range figure easily enough by using the LOS distance and angle cosine but I can't quite figure out how to get one using the LOS elevation data. The problem resides, for me, in using a 'zero' range setting.

Here's how I am trying to solve the problem.

I elect to use the 100 yard 'zero' as the start point for the angle corrected elevation adjustment, I determine the amount of correction required to adjust for the LOS distance and then apply the angle cosine to this value. But, I have a glitch in that my 100 yard 'zero' value is NOT the correct 'zero' for the shot on the current angle problem, in other words, I have no 'zero' reference point for angular trajectories.

I'm seeking alternative methods to apply the angle cosine to the required elevation correction values. (This is just for my personal enjoyment and not a life-or-death situation.)

Any clues are appreciated.

[ 06-22-2001: Message edited by: Dave King ]
 

Michael Eichele

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Jan 6, 2003
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The rifle range, or archery range or behind the co
Hey,

I am not sure exactly what math you are lookig for but to figure the angles based on a 100 yard zero is difficult. Your use was as follows:

"I elect to use the 100 yard 'zero' as the start point for the angle corrected elevation adjustment, I determine the amount of correction required to adjust for the LOS distance and then apply the angle cosine to this value. But, I have a glitch in that my 100 yard 'zero' value is NOT the correct 'zero' for the shot on the current angle problem, in other words, I have no 'zero' reference point for angular trajectories."

The only way I have been able to do it is using figures in drop inches from a zero yard zero. In other words, if the rifle was fired perfectly level you would need the inches droped at the range you desire to fire. For instance if you want to fire at a 45 degree angle at 500 yards you first find the level drop in inches and multply that number by the number below. Then deduct that number from your normal bullet drop at 500 yards and fire.

5 degrees: Normal bullet drop x .004
10 degrees: Normal bullet drop x .015
15 degrees: Normal bullet drop x .034
20 degrees: Normal bullet drop x .060
25 degrees: Normal bullet drop x .094
30 degrees: Normal bullet drop x .134
35 degrees: Normal bullet drop x .181
40 degrees: Normal bullet drop x .235
45 degrees: Normal bullet drop x .293
50 degrees: Normal bullet drop x .357
55 degrees: Normal bullet drop x .426
60 degrees: Normal bullet drop x .500

Example: 308 win using a 168 @ 2661 = -36" at 500 yards from a 300 yard zero. real drop= 81" at 500 yards. 81 multiplied by .293=24" Deduct 24 from 36 and you have 13" at 500 yards. Set the scope for 13" and fire.

I hope that helps. It maybe somthing you already know. I am not to good at the calculus needed for ballistics. Maybee you can help me??

Thanx
 

Len Backus

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Ok, here's where I show what a jerk I really am by saying I don't care about Dave's problem because my new Leica Locator Plus rangefinder will read the angle of incline and automatically tell me the corrected horizontal distance.


......unless its battery wears out in which case I will call Dave on his cellphone so he can come and help me figure it out.
 

Dave King

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May 3, 2001
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Michael Eichele

That seemed to work in the example you gave, took me a while but it looks correct.


My initial problem was that I failed to correct my 100 yard zero info and was using drop from a 100 zero vice total drop.

This litle incident led me on a nice series of experiments. I'd wanted to know the actual drop from the muzzle to the 100 yard zero so I rotated the rifle 90 degrees on the boreline and fired onto the target. my rounds impacted 3.5 inches low and 3.5 inches left (I rotated left (CCW)). I later used this info on some "cant" stuff I was working on... lots of fun and informative...

Safety tip: Be careful when you rotate your rifle 90 degrees for shooting, theres a good head thumping in the works, best to lay on your side and shoot, forget prone.

Took another good head thumping shooting a thermal vision sight on an M24... system was activiated by a pressure switch in the eyepiece (a very poorly padded eyepiece). Shot a bunch of crop damage deer with this thermal setup this last summer, had a headache for 2 days. "It sure is painful having fun sometimes."
 

Dave King

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May 3, 2001
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2,366
I've had at least one of this little devices, I believe I gave it to Ian at some point... I keep my come-up data in a "Rite in the rain" pad in the Eagle StockPack. Most of my shooting is close enough that I use a stick on data circle in the rear lenscap or just use "standard" 308 come-up data.

My only real interest in the angle issue was academic, "I like to know" things rather than just believe "near truth" that are offered in many cases.

Once I get into Ultra Long Range (> 1000) I'll be getting back into the angles more. My new rifle is waiting and I believe I'll have some more built too..."it never ends".
 

Cybra

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Dec 4, 2002
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Location
Northwest MN
Thanks, Michael, for posting that corrective bit of information. I had assumed that was what was causing minor offsets in some of my calculations, and was just about to consider the fact that the 100 yard zero was only applicable to level-fire scenarios. <knocking his head> Sometimes I really am not so swift.. Sheesh!
Anyhow, thanks for that bit of info.

Dave
 

Ian M

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May 3, 2001
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Location
Sask. Canada
Dave,
You gave me a SWAG wind-dial deely, neet little gadget that works. I have a Slope Doper in my kit, mainly because I like the name since here on the flat-*** prairies we never shoot more than 5 degrees from flat.

More rifles - no way, not the Dave King that I know!!! Nikons just arrived in the US, should have something this coming week. Hope to hunt with one in Texas next weekend. Maybe the new Hornady Bonded boolits in factory loads.

Guess you are aware of Steve Suttles situation, he is in for an operation tomorrow. Steve's in our thoughts and prayers.
 

texas

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Sep 26, 2001
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North, Texas
Ian are those the Nikon you mentioned sometime back? The main deer season ends on the 19th so if thats what you are hunting in Texas then you better hurry.
 

Len Backus

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I need to do a little more testing first. I will say, though, that it is rated to 4,000 yards.

Stay tuned.
 

Len Backus

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Same as the Vector IV

$6,700

Three day delivery

[ 01-13-2003: Message edited by: Len Backus ]
 

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