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Advanced Marksmanship High/Low Angle Shooting - When Do I need to worry about making an Angle Correction?

Jack Master

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So after listening to @Cjwise5 podcast about his experience with high angle shooting, I decided to crunch a few numbers. (I like numbers)

Question: When Do I need to worry about making an Angle Correction?

First of all, we need to understand the amount of elevation change needed to create shooting angles. As Joel said, shooting a 400yd target from the top of 2 conex boxes does not even start to have the heights needed to make angle corrections. Here is a chart the shows how many feet of elevation we need to be above or below our target to create an angle situation. You will see at 400 yards you need to be up 208 feet to get a 10 degree angle.

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But what if we do have an angle situation. How much does it effect our come-ups at angles and distances? Here is a chart for my 6.5 Creed and the corrections needed for angle shooting. This is presented in 2 ways. The first is the actual come-up and the second is the difference in come-up from our flat trajectory. I have deleted any come-ups that are less then 0.07 mil change. Studying the 2nd chart can show us the relativity of the come-up change and when we need to be aware of the conditions to make adjustments. I can start to eliminate areas of concern: any target inside 150 yards is less than 0.2Mil or .75-ish MOA of change, that is less than 1"; any target less than 20 degrees out to 300 yards

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For me, this is one of things we need to ask, does it really matter? How much will this really effect my bullet trajectory? For most shooters this will likely never be an issue. If we are mountain shooting, yes, this will matter. Most shooting ranges are on relatively flat land. I live in Iowa and I doubt I can find a range in the state that I'll need to account for high angles even if they have obstacles that add elevation. Even if I did find a steep range it might have an effect on my bullet but not likely more than 1MOA. To prove this, Lets analyse the dope charts with the elevation gain chart. I'll delete the elevation changes that will effect my bullet by less then 0.2mil or 3/4moa on the Come-up sheet. This will identify the conditions I need to look for before I even start to think about making an angle correction.

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This chart identify's the change in height I need to have before I start to worry about angle changes. I did not notice, until I did this exercise, that at each angle the height is right at 330 feet (or more) of elevation change. Now I know what to look for when asking myself "will this angle matter?". I can now ask, "Is it 300 feet of change?"... 24 feet of Conex box... not gonna matter.

Answer: When shooting upward or downward more than 300 Feet in Elevation for my Rifle.
 
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I started looking into this more recently after finally getting a mildot master. I noticed the simple cosine method was not matching up to a trusted ballistics app. MDM uses a simple cosine calculation of yardage. Here's an article I found easy to understand that talks about how cosine adjustment is not an end-all solution, and it gives a couple different formulas that are still easy.

Don't use a cosine of your dope, because that's not linear. Drop rate over yardage is a curve, so taking a simple percentage of the far-away dope is not going to account for that curve. Yardage of course will always be linear. As further proof, take 600, cut it by .707 (45°), the horizontal range is 424. Take your dope at 600, say it's 3.2 mils, cut that by .707, and it's 2.3 (rounded). But my comeup at 424 is 1.6. 11" difference.
 
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Tagging in for future reference because I want to try this out for myself, but also a few newb questions if no one cares.
1. At what point in long range shots do the quick methods given in the article begin to not work? At the apex of the arc of the bullet?
2. Obviously gravity plays a heavy hand here, so does it matter if your shooting up hill or down hill regarding the calculations for adjusted bullet trajectory?
 
Don't use a cosine of your dope, because that's not linear. Drop rate over yardage is a curve, so taking a simple percentage of the far-away dope is not going to account for that curve. Yardage of course will always be linear. As further proof, take 600, cut it by .707 (45°), the horizontal range is 424. Take your dope at 600, say it's 3.2 mils, cut that by .707, and it's 2.3 (rounded). But my comeup at 424 is 1.6. 11" difference.

Correct. That's why you never use thumbrules without first understanding the long hand math behind it. You need to know A) when does the thumbrule fall apart and B) is the thumbrule any good at all to begin with. Not all of them are.
 
Correct. That's why you never use thumbrules without first understanding the long hand math behind it. You need to know A) when does the thumbrule fall apart and B) is the thumbrule any good at all to begin with. Not all of them are.
Are you saying that as a rule of thumb don't use rules of thumb?
 
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For my 308 at 1,000 yards:

Flat dope at 0 ° = 10.6 mils
Modified Riflemans Rule applied to dope at 30° = 9.2 mils
Strelok at 30° = 9 mils

The modified "Riflemans Rule" isn't perfect, but not too bad.
 
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Thanks all for pointing out how far off the rifleman's rule can be. I've updated the post with more accurate data for my 6.5.
being over 300 feet above or below my target is the new answer.
 
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I noticed the simple cosine method was not matching up to a trusted ballistics app. MDM uses a simple cosine calculation of yardage.
As you already noted, applying the cosine to the distance causes large errors.
Don't use a cosine of your dope, because that's not linear. Drop rate over yardage is a curve, so taking a simple percentage of the far-away dope is not going to account for that curve. Yardage of course will always be linear. As further proof, take 600, cut it by .707 (45°), the horizontal range is 424. Take your dope at 600, say it's 3.2 mils, cut that by .707, and it's 2.3 (rounded). But my comeup at 424 is 1.6. 11" difference.
The modified rifleman's rule works much better for the very fact that your dope is not linear.

Applying the cosine to your dope as percentage isn't a perfect solution, but it works reasonably well.

In the example you gave above, the modified riflemans rule would have been 0.3 mils off....amounting to a 6" difference between calculated and actual at 600 yards.

All this ignoring the fact that a 45° angle would probably represent the most extreme angle possible in an actual situation.
 
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I am now questioning the accuracy of some ballistic solvers when it comes to high angle predictions. I found a new spot where I was shooting at 1100-1400yds @ -12* & 4DOF gave a .3 mil difference from FFS. Both have been spot on at smaller angles. I chose FFS & it was correct. 4DOF was .3 mil less than the actual dope. Didn't check any of the other apps but I was very surprised that 4DOF was wrong.
 
I am now questioning the accuracy of some ballistic solvers when it comes to high angle predictions. I found a new spot where I was shooting at 1100-1400yds @ -12* & 4DOF gave a .3 mil difference from FFS. Both have been spot on at smaller angles. I chose FFS & it was correct. 4DOF was .3 mil less than the actual dope. Didn't check any of the other apps but I was very surprised that 4DOF was wrong.
I did a quite similar exercise and my conclusion is that 4DOF is wrong when it comes to applying the corrections for slope shooting, the farther...the worse it gets. To the point where the 4DOF solution is clearly not making any sense at all. I don't know if it's a bug or wrong math...but flawed it is for sure.(n)

PS: I'm not surprised 4DOF is wrong, it is a hyped up app when all is said and done, the real value is in their radar data.
 
I jumped on JBM this morning to double check my 4Dof and couldn't get JBM to give any results. At 90 degrees(flat) or -45 degrees(doemhill) the output was all the same.
 
I ran some numbers in 4DOF again & it's definitely not calculating angle fire correctly. Used my conditions from last time & changed only the angle. Showed 8.7 mil @ 0*.
Said 8.3 mil @ -11* which was .5 mil off.
Said 8.2mil @ -12* which has to be bs.
A .1 mil change between-11* & -12* ?
They need to check into this & add a LH twist for my new barrel. :giggle:
 
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I ran some numbers in 4DOF again & it's definitely not calculating angle fire correctly. Used my conditions from last time & changed only the angle. Showed 8.7 mil @ 0*.
Said 8.3 mil @ -11* which was .5 mil off.
Said 8.2mil @ -12* which has to be bs.
A .1 mil change between-11* & -12* ?
They need to check into this & add a LH twist for my new barrel. :giggle:
Not only slope firing calcs are wrong...but that's another story ;)
 
Thanks for the write up. I noticed you had everything in MILS. Are those better than MOA in high angle shooting?...

Sorry. Had to... But seriously, thats an awesome write up. I'm in the same position as you for not needing to shoot high angle, but the theory is pretty awesome. Saving this thread for future reference.
 
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You're welcome. I'm my AO I very rarely get to shoot at 0* angle or over flat ground. Usually shooting across canyons.
 
I have shot plenty with the Kestrel using the AB solver and that math has been dead on out to a 1600m. I’ve used the rules of thumb and they’re sometimes pretty close but accounting for both airline distance and gravity distance without doing plenty of math will have some short comings.

The hardest part of shooting at high angles is building the position, and having a solid tripod. Having a good range finder to give you the angle or at least some tool to give you the angle is also very important.

Overall though most people will never take a high angle shot.
 
Doing more number crunching of the the data above we could set a value to look for in the field. Multiply the yardage by the first number in the angle.

10 Deg = 1 x 625yards = 625
20 Deg = 2 x 325yds = 650
30 Deg = 3 x 250yds = 750

If I used 600 as the thread-hold for knowing I need an angle correction, I could Look for this in the field.

Example:
Range finder says 300 yards (line of light) at 25 degress
Simple head math is 300x2.5 is more than 600 so I know I need an angle correction.

Example
Range finder days 450 yards at 12 degrees
head math of 450x1.2 = 540 --> No Angle correction needed.

This will be a different value for each rifle or caliber so you'll have to find yours. I'm curious if this number might be your rifle MPH for wind x100 as a starting point.
 
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