Recommended Ballistic Computer
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Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
No, I did mean fluid and yes, gas like ambient air, does behave like a fluid in its motions around the terrain we shoot on.
I have yet to see anyone propose any theorums on negotiating the visual distortions of light by air/humidity.
As I said before, if you can figure it out, let us all know cause we are all ears.
Jerry
I have yet to see anyone propose any theorums on negotiating the visual distortions of light by air/humidity.
As I said before, if you can figure it out, let us all know cause we are all ears.
Jerry
Jerry is correct. Gas and liquid are both fluids. A lot of people don't understand the difference, and use "fluid" and "liquid" interchangeably.
Last edited:
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
The fact that a liquid or a gas is considered a "fluid' took me by surprise too, some number of years ago. ("Computational Fluid Dynamics" is used to calculate air flows over wings, gas flows inside rocket engines or gun barrels, etc).
Jerry, have you ever had an opportunity to do the test(s) you describe? What were the results? (I have never had the opportunity to do these tests, and am most curious).
A change in the air's pressure, temperature, or humidity should not have an effect on the apparent target position. And as far as I know, neither should a change in light intensity or angle (though that does go against some generally received shooting wisdom!).
Something that will bend light is a density gradient. If the temperature of the air varies with height, over the distance you are looking through, that is will bend light rays (in the direction of the lower density, which is the direction of higher temperature). This is how mirages work (the kind you get on the ocean or in the dessert, where you see a distant object - not the "mirage" we talk of in shooting).
An old shooter pointed out to me a most interesting observation: land surveyors do not (to his and my knowledge) make any compensation for bending of light when they do surveys. And their precision is deeply sub-MOA (they measure in seconds of angle).
Cheers,
Jerry, have you ever had an opportunity to do the test(s) you describe? What were the results? (I have never had the opportunity to do these tests, and am most curious).
A change in the air's pressure, temperature, or humidity should not have an effect on the apparent target position. And as far as I know, neither should a change in light intensity or angle (though that does go against some generally received shooting wisdom!).
Something that will bend light is a density gradient. If the temperature of the air varies with height, over the distance you are looking through, that is will bend light rays (in the direction of the lower density, which is the direction of higher temperature). This is how mirages work (the kind you get on the ocean or in the dessert, where you see a distant object - not the "mirage" we talk of in shooting).
An old shooter pointed out to me a most interesting observation: land surveyors do not (to his and my knowledge) make any compensation for bending of light when they do surveys. And their precision is deeply sub-MOA (they measure in seconds of angle).
Cheers,
Max Owner
CGN Ultra frequent flyer
Had a chance to get my 308 out with Hornady factory match ammo. Used the Isnipe program using G7 ballistics and got my first 5 shots on a steel sheep at 500 yards.
The rest of the box were all hits, too.
I had some issues before and was becomming very discouraged with Isnipe. But my error was using the default G1 ballistics. Not G7.
The rest of the box were all hits, too.
I had some issues before and was becomming very discouraged with Isnipe. But my error was using the default G1 ballistics. Not G7.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Daniel, I am sorry but have no way to scientifically describe what is happening but the image you see does change location.
Do that simple test and it is pretty 'enlightening'.
Again, I am not saying the target or rifle is moving. What I am saying is that the location of the sun vs the ambient conditions can cause an apparent change in position.
The shooting mirage we all talk about is the simplest way for someone to see lights effect on aiming. So does shooting on a variable cloudy day where the sun pops in and out of the clouds.
It can have some marked effects depending on the air conditions.
And yes, if I had a way to quantify this, I would be so much happier cause it would really improve my condition doping skills.
If anyone has a technique even if simply anedoctal or voodoo, I am all ears.
This effect likely isn't a big issue with open sights but it sure shows up with scopes.
Try it and let me know...
Jerry
Do that simple test and it is pretty 'enlightening'.
Again, I am not saying the target or rifle is moving. What I am saying is that the location of the sun vs the ambient conditions can cause an apparent change in position.
The shooting mirage we all talk about is the simplest way for someone to see lights effect on aiming. So does shooting on a variable cloudy day where the sun pops in and out of the clouds.
It can have some marked effects depending on the air conditions.
And yes, if I had a way to quantify this, I would be so much happier cause it would really improve my condition doping skills.
If anyone has a technique even if simply anedoctal or voodoo, I am all ears.
This effect likely isn't a big issue with open sights but it sure shows up with scopes.
Try it and let me know...
Jerry
That was what I was trying to get at with Jerry - I wanted to know what 'affects' he was speaking of. If it's mirage as he's noted, well that's totally a perception issue to our eyes and to your point above, should not affect the target position as far as the gun and scope go... that is until we look down the scope.
If I understand this correctly, if the gun/scope remain in the same position all day, it will shoot in the same spot all day, assuming environmental conditions remain the same.
I thought perhaps Jerry was referring to how light and inherent shadows affect our view of the target (like mirage), or perhaps how the light (sun) heats a barrel.
As for mirage, its not quantifiable from what I know and therefore would likely impossible to measure and compensate.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Which is pretty much my orig point about the benefit of ballistic programs.
They are an aid absolutely and the hand held units are so much easier to use today, BUT something as simple as mirage (sun light vs air), has such a massive effect on POA AND is damn near impossible to quantify, that one shot hits at extreme distances has alot more to do with shooting skill AND experience then the number generated by a computer.
I have seen some great shooters do amazing things and hit dead on in conditions I would have shot better if my eyes were closed.
We haven't even discussed the effects of this ever moving bumpy fluid we shoot through.
Look up Thermal. That will be good for a chat.
Jerry
Sources of Ballistic Program Inaccuracies
by Linden B. (Lindy) Sisk
Last Revision January 30, 2010
--------------------------------------------------------------------------------
Shooters using ballistic programs often find that their field shooting data does not precisely agree with the output from their program.
In addition, shooters comparing the outputs of different programs often find significant discrepancies between the programs. Why?
Below are listed the cause of some inaccuracies in the elevation predictions of ballistic programs. Windage calculations are beyond the scope of this article.
Uncalibrated scope clicks. For example, Leupold M1 dials I have tested are closer to 1 inch per hundred yards than 1 MOA. With a typical .308 load at 1000 yards, the difference in point of impact is about 20 inches. If you don't know how to check that calibration, you may find this article useful: Optically Checking Rifle Scopes
Normal variations in muzzle velocity. A good load may have a muzzle velocity standard deviation of 15 feet per second. That means that about two-thirds of the shots will fall in the range from 15 fps per second above the average velocity to 15 feet per second below the average. At 1000 yards with a typical .308 load, that range of variations will cause shots distributed over a 10 inch range. Nota bene: About one third of the shots will have variations from the average which are even greater. There are many causes of this velocity variation, and they are beyond the scope of this article.
Temperature variations in muzzle velocity. A pretty good powder will exhibit a variation in muzzle velocity of 1 foot per second per Fahrenheit degree. If you chronographed your load at 85 degrees and are shooting at 55 degrees, your muzzle velocity may be 30 feet per second slower than you think it is. I have measured variations as large as 5 feet per second per Fahrenheit degree. The only way to know how big that variation is, is to test it. In addition, my experience has been that the standard deviation of the muzzle velocity increases at low temperatures.
Muzzle velocity measurement errors. Do you believe your chronograph is accurate? The screen spacing of most chronographs is too short for accurate measurement. Some chronographs like the Oehler 35 series allow extending the spacing. The clock frequency of many chronographs is too slow to get accurate and consistent measurements, i.e., more than one shot with the identical muzzle velocity will be displayed with different measurements. Other common problems with chronograph data is failing to compensate for the distance between the muzzle and the chronograph screens, and failing to fire enough rounds to have a good average velocity. People with little understanding of statistics may have a very vague idea of what the chronograph output means. See Statistics for Rifle Shooters
Ballistic coefficient variations. Most manufacturers publish only G1 BCs for their bullets. The G1 coefficient doesn't match very well the shape of modern boattail bullets. To accomodate that, Sierra publishes BCs for their bullets in velocity ranges. However, many ballistic programs are not set up to handle multiple BC values. A better match to boattail bullets is the G7 BC, which will produce a better calculation of bullet velocity at range, which is useful to shooters who are operating near the transonic range of their bullets. Some bullets exhibit unpredicable behaviour in the transonic range. The Sierra 168 grain Matchking is one such bullet.
One source of G7 BCs produced by extensive testing is the book Applied Ballistics for Long Range Shooting by Bryan Litz. I highly recommend this book for anyone serious about shooting at extended distances.
In addition, the online program JBM Ballistics has some G7 BCs in its bullet library. It does not tell you what the G7 BC is - just select the a bullet with the label "(Litz)" after the listing in the bullet library. If there is no such label after the bullet you are using, a G7 coefficient is not available. Also select G7 in the main screen.
Range uncertainty. This is a prime cause of differences between the ballistic program output and field shooting data at long range. At 1000 yards with our typical .308 load, a range error of 20 yards will cause an elevation error of about 18 inches, which is 0.5 mil or almost 2 MOA. You may believe your laser rangefinder is accurate - but a one percent error at 1000 yards is 10 yards, and that's assuming that you actually managed to laser the target. The manufacturer of the common Leica 1200 claims an accuracy of +/- 0.5 percent beyond 800 yards.
Elevation variations caused by the headwinds or tailwinds. Headwinds slightly increase the drag on the bullet, and tailwinds reduce it. Not all ballistics programs correctly model this effect.
Aerodynamic jump. This is Bryan Litz's description of this factor: "Aerodynamic jump is what causes groups to slant when shot in varying wind conditions. Basically, when the bullet exits the muzzle into a cross wind, the bullet tries to yaw slightly to align itself with the airflow. When the bullet yaws to the side, gyroscopic action causes it to nose up or down by a small amount depending on the wind direction. This initial yaw has an effect on the trajectory, and is known as aerodynamic jump. The more severe the cross wind, the more pitch the bullet ends up with. Flying to the target at a pitch angle will result in an elevation error that's proportional to crosswind." From: Extending the Maximum Effective Range of Small Arms. That's a good article which describes some of the limitations of existing ballistic programs.
The Eötvös effect. This is an elevation variation caused by the earth's rotation. It is of most significance on long shots taken directly due east or west. Some ballistics program do not correctly model this effect. Bryan's Litz's book previously referenced has a section on how to calculate that effect if your ballistic program does not. The magnitude of this variation might be in the range of 10 inches maximum difference on a 1000 yard shot between a due east shot and a due west shot, depending on your lattitude.
Incorrect specification of atmospheric parameters. Many shooters do not understand the difference between station pressure and barometric pressure referenced to sea level. See Barometric Pressure and Ballistic Software.
Error in Inclined Shot Calculations. Many ballistic program do not correctly compensate for the difference between an uphill shot, where gravity slightly hinders the bullet, and a downhill shot, where gravity is slightly aiding the bullet. For example, on a 900 yard shot at a 30 degree angle, the difference between an uphill shot and a downhill shot is about one MOA. The magnitude of this difference increases with the angle. Most programs I have seen are doing a calculation appropriate to an uphill shot, so what one might do to compensate for that is to hold a little low on a downhill shot.
An additional possible error on an inclined shot is failure to compensate for the difference in air density between the firing position and the target. For example, on a 900 yard shot at a 30 degree angle, the altitude difference between the firing position and the target is 1350 feet. No ballistic program I am aware of attempts to compensate for that difference.
Parallax error caused by improper adjustment. When looking through the scope at the target, the reticle should not appear to move relative of the target when you make a slight movement of your head. If it does, parallax error is present and should be corrected.
Zero errors. If your hundred yard zero is off by a quarter of an inch, at 1000 yards your point of aim will be off by 2.5 inches.
Shooter variations. We have seen two shooters have different points of impact on the same target at long distance using the same rifle and load. That's because of differences in the way the rifle is held by the shooter.
Differences in atmospheric modeling between the programs.
Now What?
Now that we know some of the causes, what can we do?
We can systematically modify the program output by shooting long-range with our load, and then adjusting the BC input to the program until the program output matches the shooting data. I typically do this at a range of 1000 yards with a .308. Nota bene: it should be done at a range and under conditions where you know the bullet has not entered the transonic region. We might say the bullet has entered the transonic region if its velocity has decreased to within 110 percent of the speed of sound. (The speed of sound is about 1125 feet per second at 68 degrees F. It varies only with temperature.) So, if the speed of sound is 1125 feet per second, we might say the bullet is in the transonic region when the speed has dropped to 1238 fps.
If other sources of error discussed above have not been ruled out, it should be obvious that the correction obtained by this process will apply only to this load fired from one specific rifle with one specific scope - maybe.
Understand from this discussion that no ballistic program can produce an output sufficiently accurate to guarantee a first-round hit at ranges beyond a few hundred yards. A ballistic program is correctly used to get you close to that first-round hit under conditions you don't normally shoot in. An example is training with your rifle and load at sea level, and then trying to make a high-altitude shot.
When someone says that their un-tuned ballistic program was "right on at 1000 yards", I generally conclude that if they are telling the truth, they were lucky enough to have offsetting errors.
--------------------------------------------------------------------------------
This file is: http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Programs/index.html
© 2009, 2010 by Linden B. (Lindy) Sisk
Permission is granted to print or photocopy the entire article intact, including this notice. All other rights reserved.
by Linden B. (Lindy) Sisk
Last Revision January 30, 2010
--------------------------------------------------------------------------------
Shooters using ballistic programs often find that their field shooting data does not precisely agree with the output from their program.
In addition, shooters comparing the outputs of different programs often find significant discrepancies between the programs. Why?
Below are listed the cause of some inaccuracies in the elevation predictions of ballistic programs. Windage calculations are beyond the scope of this article.
Uncalibrated scope clicks. For example, Leupold M1 dials I have tested are closer to 1 inch per hundred yards than 1 MOA. With a typical .308 load at 1000 yards, the difference in point of impact is about 20 inches. If you don't know how to check that calibration, you may find this article useful: Optically Checking Rifle Scopes
Normal variations in muzzle velocity. A good load may have a muzzle velocity standard deviation of 15 feet per second. That means that about two-thirds of the shots will fall in the range from 15 fps per second above the average velocity to 15 feet per second below the average. At 1000 yards with a typical .308 load, that range of variations will cause shots distributed over a 10 inch range. Nota bene: About one third of the shots will have variations from the average which are even greater. There are many causes of this velocity variation, and they are beyond the scope of this article.
Temperature variations in muzzle velocity. A pretty good powder will exhibit a variation in muzzle velocity of 1 foot per second per Fahrenheit degree. If you chronographed your load at 85 degrees and are shooting at 55 degrees, your muzzle velocity may be 30 feet per second slower than you think it is. I have measured variations as large as 5 feet per second per Fahrenheit degree. The only way to know how big that variation is, is to test it. In addition, my experience has been that the standard deviation of the muzzle velocity increases at low temperatures.
Muzzle velocity measurement errors. Do you believe your chronograph is accurate? The screen spacing of most chronographs is too short for accurate measurement. Some chronographs like the Oehler 35 series allow extending the spacing. The clock frequency of many chronographs is too slow to get accurate and consistent measurements, i.e., more than one shot with the identical muzzle velocity will be displayed with different measurements. Other common problems with chronograph data is failing to compensate for the distance between the muzzle and the chronograph screens, and failing to fire enough rounds to have a good average velocity. People with little understanding of statistics may have a very vague idea of what the chronograph output means. See Statistics for Rifle Shooters
Ballistic coefficient variations. Most manufacturers publish only G1 BCs for their bullets. The G1 coefficient doesn't match very well the shape of modern boattail bullets. To accomodate that, Sierra publishes BCs for their bullets in velocity ranges. However, many ballistic programs are not set up to handle multiple BC values. A better match to boattail bullets is the G7 BC, which will produce a better calculation of bullet velocity at range, which is useful to shooters who are operating near the transonic range of their bullets. Some bullets exhibit unpredicable behaviour in the transonic range. The Sierra 168 grain Matchking is one such bullet.
One source of G7 BCs produced by extensive testing is the book Applied Ballistics for Long Range Shooting by Bryan Litz. I highly recommend this book for anyone serious about shooting at extended distances.
In addition, the online program JBM Ballistics has some G7 BCs in its bullet library. It does not tell you what the G7 BC is - just select the a bullet with the label "(Litz)" after the listing in the bullet library. If there is no such label after the bullet you are using, a G7 coefficient is not available. Also select G7 in the main screen.
Range uncertainty. This is a prime cause of differences between the ballistic program output and field shooting data at long range. At 1000 yards with our typical .308 load, a range error of 20 yards will cause an elevation error of about 18 inches, which is 0.5 mil or almost 2 MOA. You may believe your laser rangefinder is accurate - but a one percent error at 1000 yards is 10 yards, and that's assuming that you actually managed to laser the target. The manufacturer of the common Leica 1200 claims an accuracy of +/- 0.5 percent beyond 800 yards.
Elevation variations caused by the headwinds or tailwinds. Headwinds slightly increase the drag on the bullet, and tailwinds reduce it. Not all ballistics programs correctly model this effect.
Aerodynamic jump. This is Bryan Litz's description of this factor: "Aerodynamic jump is what causes groups to slant when shot in varying wind conditions. Basically, when the bullet exits the muzzle into a cross wind, the bullet tries to yaw slightly to align itself with the airflow. When the bullet yaws to the side, gyroscopic action causes it to nose up or down by a small amount depending on the wind direction. This initial yaw has an effect on the trajectory, and is known as aerodynamic jump. The more severe the cross wind, the more pitch the bullet ends up with. Flying to the target at a pitch angle will result in an elevation error that's proportional to crosswind." From: Extending the Maximum Effective Range of Small Arms. That's a good article which describes some of the limitations of existing ballistic programs.
The Eötvös effect. This is an elevation variation caused by the earth's rotation. It is of most significance on long shots taken directly due east or west. Some ballistics program do not correctly model this effect. Bryan's Litz's book previously referenced has a section on how to calculate that effect if your ballistic program does not. The magnitude of this variation might be in the range of 10 inches maximum difference on a 1000 yard shot between a due east shot and a due west shot, depending on your lattitude.
Incorrect specification of atmospheric parameters. Many shooters do not understand the difference between station pressure and barometric pressure referenced to sea level. See Barometric Pressure and Ballistic Software.
Error in Inclined Shot Calculations. Many ballistic program do not correctly compensate for the difference between an uphill shot, where gravity slightly hinders the bullet, and a downhill shot, where gravity is slightly aiding the bullet. For example, on a 900 yard shot at a 30 degree angle, the difference between an uphill shot and a downhill shot is about one MOA. The magnitude of this difference increases with the angle. Most programs I have seen are doing a calculation appropriate to an uphill shot, so what one might do to compensate for that is to hold a little low on a downhill shot.
An additional possible error on an inclined shot is failure to compensate for the difference in air density between the firing position and the target. For example, on a 900 yard shot at a 30 degree angle, the altitude difference between the firing position and the target is 1350 feet. No ballistic program I am aware of attempts to compensate for that difference.
Parallax error caused by improper adjustment. When looking through the scope at the target, the reticle should not appear to move relative of the target when you make a slight movement of your head. If it does, parallax error is present and should be corrected.
Zero errors. If your hundred yard zero is off by a quarter of an inch, at 1000 yards your point of aim will be off by 2.5 inches.
Shooter variations. We have seen two shooters have different points of impact on the same target at long distance using the same rifle and load. That's because of differences in the way the rifle is held by the shooter.
Differences in atmospheric modeling between the programs.
Now What?
Now that we know some of the causes, what can we do?
We can systematically modify the program output by shooting long-range with our load, and then adjusting the BC input to the program until the program output matches the shooting data. I typically do this at a range of 1000 yards with a .308. Nota bene: it should be done at a range and under conditions where you know the bullet has not entered the transonic region. We might say the bullet has entered the transonic region if its velocity has decreased to within 110 percent of the speed of sound. (The speed of sound is about 1125 feet per second at 68 degrees F. It varies only with temperature.) So, if the speed of sound is 1125 feet per second, we might say the bullet is in the transonic region when the speed has dropped to 1238 fps.
If other sources of error discussed above have not been ruled out, it should be obvious that the correction obtained by this process will apply only to this load fired from one specific rifle with one specific scope - maybe.
Understand from this discussion that no ballistic program can produce an output sufficiently accurate to guarantee a first-round hit at ranges beyond a few hundred yards. A ballistic program is correctly used to get you close to that first-round hit under conditions you don't normally shoot in. An example is training with your rifle and load at sea level, and then trying to make a high-altitude shot.
When someone says that their un-tuned ballistic program was "right on at 1000 yards", I generally conclude that if they are telling the truth, they were lucky enough to have offsetting errors.
--------------------------------------------------------------------------------
This file is: http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Programs/index.html
© 2009, 2010 by Linden B. (Lindy) Sisk
Permission is granted to print or photocopy the entire article intact, including this notice. All other rights reserved.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
That was likely THE BEST info on error in ballistic programs. Trevor60 thanks for posting.
Now for those who are now totally discouraged and figure hitting anything at distances over 50ft an impossibility, take heart.
The key is get your rifle, your ammo, scope, rangefinder AND a ballistics chart/software and go shoot it.
The ballistics program will get you close enough to see the impact. Then manually adjust your real world adjustments into the program. Remember, you are tuning for your series of errors....
If the load is good, the scope tracking well and the shooter doing his job, the 'new' chart will work under most conditions likely to be experienced. Just use the adj. data again, and if it is working, you will hit what you want to.
I take a number of shooters out LR plinking each summer and they almost always run into this concern that their program doesn't agree with reality. to which I say, who cares.
If your data agrees with your set up and that gets you on target, does it really matter if the number is different from what the computer originally spat out?
Have fun... Shoot LOOOOONG
Jerry
PS was out plinking with my Savage Shilen 223 yesterday and went out to 1210yds (per Swaro rangefinder). The JBM data using Bryan's data for my 80gr Amax was actually pretty darn close. I was within 1 min of data which likely accounts for a different zero and or ambient conditions and/or scope or see list above.
Now for those who are now totally discouraged and figure hitting anything at distances over 50ft an impossibility, take heart.
The key is get your rifle, your ammo, scope, rangefinder AND a ballistics chart/software and go shoot it.
The ballistics program will get you close enough to see the impact. Then manually adjust your real world adjustments into the program. Remember, you are tuning for your series of errors....
If the load is good, the scope tracking well and the shooter doing his job, the 'new' chart will work under most conditions likely to be experienced. Just use the adj. data again, and if it is working, you will hit what you want to.
I take a number of shooters out LR plinking each summer and they almost always run into this concern that their program doesn't agree with reality. to which I say, who cares.
If your data agrees with your set up and that gets you on target, does it really matter if the number is different from what the computer originally spat out?
Have fun... Shoot LOOOOONG
Jerry
PS was out plinking with my Savage Shilen 223 yesterday and went out to 1210yds (per Swaro rangefinder). The JBM data using Bryan's data for my 80gr Amax was actually pretty darn close. I was within 1 min of data which likely accounts for a different zero and or ambient conditions and/or scope or see list above.
armagedon41
New member
- Location
- Edmonton, Alberta
Im voteing repost that under a better named thread and get it stikkied. GREAT Info.
