Ballistic charts and drop, need help...

Evil_Dark

Evil_Dark

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Hi there,

I'm learning a lot these past months about ballistics for long range and extreme long range shooting. So there's a lot to learn, but the data is entering the head at a good rate ;)

When I try to apply some data to the fields, mismatch occurs and part of learning is to understand why. Now that I have a chronograph and a meteo meter, there is not supposed to have a lot of "gray zone" left...

So I shooted at 300 and 500 yards today, and I cannot match my results with any of the charts that I create with ballistic calculators.

So here is the data collected about meteo:
15 degrees Celcuis, 30%humidity, 30.23 in.Hg of pressure, altitude 475 feets.
My average velocity was 2587fps for a .308Win, 168gr Hornady Match HPBT bullet rated at .226 G7 bal. coeff.

Not sure about the zero of my scope(supposed to be zeroed at 200Y), but at 300 yards I had to dial a 1MOA drop, and at 500 yards I had to dial 9.5MOA, both to be dead-on vertically (grouping average).
The group at 500yards was 5,5"(5-15km/h winds), but the vertical spread was 3" so not so bad...

So heres the math I'm doing and which did not match any of my charts:

If I have -1moa at 300Y and 9.5moa at 500Y, this mean if I zero my rifle at 300 yards, I will have a 8moa drop at 500y, right? But If I enter 2587fps within all others variables on a ballistic calculator, I'm far away from these results...
I would like to understand why.

Thanks for the help!

Dark
 
Drop is an exponential drop curve, not linear, so your assumption that changing your zero from 2 to 300 yards should change your 500yard adjustment by the same amount is wrong.

I think that's what you're asking?
 
Gunneegoogoo said:
Drop is an exponential drop curve, not linear, so your assumption that changing your zero from 2 to 300 yards should change your 500yard adjustment by the same amount is wrong.
Click to expand...
If my turret is at 1moa at 300y and I zero it (turn the cap back at 0 without turning the turret mechanic), at 500y now I will have to dial 8.5moa instead of 9.5moa...


Gunneegoogoo said:
I think that's what you're asking?
Click to expand...
Not really. I want to correlate my drop with a chart, because my drop seems to be a lot more than usual charts at my given velocity.

Dark
 
is your zero correct for 200m? That doesn't seem like much adjustment between 200-300.

only reason I ask is that my chart data
nosler hpbt 168gr, alt 250, temp 70

100 zero
200 2moa
300 4.8moa
500 11.67moa
 
Is your sight height accurate? that plus atmospherics makes a pretty big difference. I'd re-zero at 100 yd and try again. I'd also check the tracking on your scope, could be off.
 
First you should confirm what pressure reading your weather station gives. If you have the option of station pressure, then set it to that and set your elevation to "0" feet in your ballistic calc. If your weather station gives a standard baro pressure then its likly compensated to sea level. In that case youll have to add your elevation above sea level.

Next you have to have a velocity for your ammo at the current ammo temperature. Your muzzle velocity can change well over 100fps from a cold spring day to a warm spring day.

Another possible issue is with your scopes tracking. Its extremely rare to have a scope tracks perfectly. How much is yours off? You wont know until you test it.
 
LeftFootOfDoom said:
is your zero correct for 200m? That doesn't seem like much adjustment between 200-300.

only reason I ask is that my chart data
nosler hpbt 168gr, alt 250, temp 70

100 zero
200 2moa
300 4.8moa
500 11.67moa
Click to expand...
I'm absolutely sure that my zero is not OK at 200y.
In your chart, you have 6.87MOA of difference between 300 and 500. I have 8.5MOA.

My scope seems to repeat very well, but I did'nt tracked it with a ruler to see if there is precisely 1/4MOA per click. I'll have to test it for sure, as I've heard that a LOT of GOOD scopes are a bit off...

Dark
 
Using the data provided, if I choose 267 yards as the zero range, I get this from JBM:

267 zero
300 1.0 MOA
400 4.5 MOA
500 8.5 MOA

Off by 1 MOA at 500 from what you got. That is fairly close. The 1 MOA difference could be due to a number of things. To answer your question about zeroing at 300, if I change the zero to 300, I get this:

300 zero
400 3.5 MOA
500 7.5 MOA

Yes, it just shifts by the difference. If you zero at 300 when you previously had to put on 1 MOA at 300 and 9.5 MOA at 500, your new 500 yard come-ups will be 8.5 MOA.
 
The shift is a pretty basic thing btw. It is used a lot in PRS shooting due to the tight time constraints. For example (using the first set of data with the 267 yard zero), if you had a target at 300, one at 400 and one at 500 and you had to engage them very quickly, a common approach would be to dial on 4.5 MOA. Then hold under 3.5 MOA on the 300 yard target, hold center on the 400 yard target and hold 4.0 MOA over on the 500 yard target using the reticle.
 
Evil_Dark said:
Hi there,

I'm learning a lot these past months about ballistics for long range and extreme long range shooting. So there's a lot to learn, but the data is entering the head at a good rate ;)

When I try to apply some data to the fields, mismatch occurs and part of learning is to understand why. Now that I have a chronograph and a meteo meter, there is not supposed to have a lot of "gray zone" left...

So I shooted at 300 and 500 yards today, and I cannot match my results with any of the charts that I create with ballistic calculators.

So here is the data collected about meteo:
15 degrees Celcuis, 30%humidity, 30.23 in.Hg of pressure, altitude 475 feets.
My average velocity was 2587fps for a .308Win, 168gr Hornady Match HPBT bullet rated at .226 G7 bal. coeff.

Not sure about the zero of my scope(supposed to be zeroed at 200Y), but at 300 yards I had to dial a 1MOA drop, and at 500 yards I had to dial 9.5MOA, both to be dead-on vertically (grouping average).
The group at 500yards was 5,5"(5-15km/h winds), but the vertical spread was 3" so not so bad...

So heres the math I'm doing and which did not match any of my charts:

If I have -1moa at 300Y and 9.5moa at 500Y, this mean if I zero my rifle at 300 yards, I will have a 8moa drop at 500y, right? But If I enter 2587fps within all others variables on a ballistic calculator, I'm far away from these results...
I would like to understand why.

Thanks for the help!

Dark
Click to expand...

Your zero is not right... confirm with an accurate distance from you to target... many ranges are not correct to the target backstop. Start at 100yds.. use the same rangefinder for all distances so hopefully the ranging error is consistent.

Confirm the actual scope travel .. MOA or MRAD is not Inch or CM... a scope with a small adjustment error can carry through to a significant number with a bunch of elevation added.

Scope height, actual velocity, true Ambient, Wind... and the big one... true BC for your rifle... will all affect where that bullet lands.

Ballistic programs are merely approximations based on your input data. Errors here, create errors in the output... but you will "hit paper".

Use a program that allows you tweak the adjusts based on your real world shooting... this will change as the rifle changes. So if the program suggests you need 9 1/2 mins to hit a distance but you use 9 mins with reliability... 9 it is

Position of the sun can have a profound effect on your actual come ups needed so never assume that a number on a LCD screen is gospel.... understand the variables and what will affect your results... shoot lots so you know what your system will actually do in the field... and how to tweak the data

Make sure you are consistent enough to deliver the same follow through so the bullet will see the same launch regardless of position... etc, etc, etc.

As long as you are improving and the results are getting consistent, over time, you will have data that suits your system and you can trust.

Jerry
 
Mystic Precision said:
... and the big one... true BC for your rifle... will all affect where that bullet lands.
Jerry
Click to expand...

Do you mean that BC of the bullet is changing from rifle to rifle?
Is it better to tweak BC on a ballistic program calculator or Velocity in order to get the right chart based on real life?

The G7 ballistic calculator can allow the "trajectory validation", ( http://www.gseven.com/ballistic-program ) so you are entering "real life drop results" along all others data and it will give you a chart based on these results. I can see that the program changes the FPS to build a chart that match my results. I've heard other people changing the ballistic coefficient of the bullet to come close charts results with real life. Is there a better way to do that the other?

Dark
 
Evil_Dark said:
Do you mean that BC of the bullet is changing from rifle to rifle?
Is it better to tweak BC on a ballistic program calculator or Velocity in order to get the right chart based on real life?

The G7 ballistic calculator can allow the "trajectory validation", ( http://www.gseven.com/ballistic-program ) so you are entering "real life drop results" along all others data and it will give you a chart based on these results. I can see that the program changes the FPS to build a chart that match my results. I've heard other people changing the ballistic coefficient of the bullet to come close charts results with real life. Is there a better way to do that the other?

Dark
Click to expand...

Strelok has a "truing" feature. I don't see why one should have to change the BC. It's a constant (well, it is for mortals like us - Litz understands that it changes as it moves downrange, but Sheldon Cooper also understands the 19th dimension.....).
 
here is your first problem.........your range has the following

100 yard target frame
200 yard target frame
300 meter target frame
500 meter target frame
600 yard target frame

without a proper laser range finder on that range your never going to know what it is your trying to accomplish. still doesn't account for alot of your errors but knowing the target distances will take some of the error out and get you closer.
 
Evil_Dark said:
Do you mean that BC of the bullet is changing from rifle to rifle?
Is it better to tweak BC on a ballistic program calculator or Velocity in order to get the right chart based on real life?

The G7 ballistic calculator can allow the "trajectory validation", ( http://www.gseven.com/ballistic-program ) so you are entering "real life drop results" along all others data and it will give you a chart based on these results. I can see that the program changes the FPS to build a chart that match my results. I've heard other people changing the ballistic coefficient of the bullet to come close charts results with real life. Is there a better way to do that the other?

Dark
Click to expand...

Yes, BC is a moving target... Bore roughness, number of lands and grooves and how that engraves in the bullet, muzzle velocity, twist rate, mag feeding damage can all affect the ACTUAL real world flying through the air BC. Even ambient conditions can have slight affects on this (yes, the programs try to adjust for this in the math IF you can input good info)

best part... as your bore wears and affects the bullets differently, the drop chart will need tweaking (either caused by a change in bullet drag and/or muzzle velocity)

BC is most definitely not a fixed number even from the manf of the bullets... lot to lot variation can and does affect the shape you get in the box... just compare meplat diameters from lot to lot of the same bullet. Berger is one of the best for keeping up with current lot data... and if you track their BCs, they most certainly change them from time to time.. Smart for them and a great service to us shooters.

So I always get a giggle when shooters swear that this bullet must do XYZ and their program will give them accuracy to a 1/4" at 1 million miles. Shoot some bullets and you will quickly see what I mean.

Hell, take the same box of bullets .... load them in a few rifles at similar muzzle velocities and group them on paper at LR.. see what you get.

Being involved in Team shooting with what should be near identical set ups, we always have to tweak what actually happens on target cause things are never perfectly identical. Small adjustments.. sure, but adjustments never the less.

But the solution is very simple.... I print my drop chart and then mark in the corrections I need for my set up. Confirmed over many trips at multiple distances. This was confirmed with my rangefinder, my scope, my ammo, my rifle, my shooting, my real estate. Did I get dead reliable and repeatable drop charts to within 1/4 min out to 1000yds... YEP.

Can you take this data, enter it back into the ballistics software to "tweak" the values so it matches... you can now... and once you do, the software will adjust these tweaks as you go to different locations. So you are creating perfectly "flawed" results that suit you and your set up precisely.

Would it work for another rifle using the same cartridge and bullet.... maybe, but I wouldn't bet a double double on it

Jerry
 
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