I'm one of those people who come here to learn. Why don't you provide that further context in your own thread instead of mucking up this one?
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Hornady 4DOF Ballistic Program
- Thread starter AaronSkipDavidson
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I'm one of those people who come here to learn. Why don't you provide that further context in your own thread instead of mucking up this one?
I must admit, I too fell for the fancy marketing hype of the 4DOF system. Then, however, I read Bryan's article and saw the fallacy of "4 DOF" solvers from a physics (equations of motion) and simulation background….
Personally I didn't see the article as promoting or denigrating a certain brand's profitable products (bullets). Bryan is not judging Hornady's bullets against any other company, Berger or what have you. What he IS promoting is his opinion on Hordandy's public claims about their "first of its kind" solver. As he says, the truth is that both JBM and AB have had free online solvers capable of predicting spin drift, aerodynamic jump, and coriolis effect.
Personally I didn't see the article as promoting or denigrating a certain brand's profitable products (bullets). Bryan is not judging Hornady's bullets against any other company, Berger or what have you. What he IS promoting is his opinion on Hordandy's public claims about their "first of its kind" solver. As he says, the truth is that both JBM and AB have had free online solvers capable of predicting spin drift, aerodynamic jump, and coriolis effect.
Are you really making the claim that a six figure doppler radar measuring system is inferior to a budget system comprised of acoustic microphones?
That's not what was claimed. However, that can definitely be the case, depends on how knowledgeable the people running that 6 figure system are. In a prefect world, maybe, but barely, to the extent that its a moot point really. It is a lot more difficult to derive accurate results from that complex system than the system AB uses. We can attain very accurate data relatively easily and is why we have a large database of very accurate drag curves.
But all of that is beside the point. Our data with our system is already pretty much as accurate as with the doppler. The difference, and what is being claimed by Hornady, is that they are getting data from the radar to use in their "4th DOF" which calculates spin drift and aerodynamic jump. This is false because the data required for those calculations can not be derived from the radar data. The AB solver uses dedicated equations that have been repeatedly tested and tuned through live fire testing, but not just shooting over a microphone or radar because that doesn't do anything for these aspects, to calculate spindrift and aerodynamic jump very accurately. Hornady estimates the various coefficients needed for their "4th DOF". So, you have a claimed "more precise" system that is based on estimates. Precision and estimates don't generally go hand in hand. Especially when there are already highly accurate methods being used that don't rely on estimations.
Long story short, practically the radar isn't any more accurate than the system AB uses. And it doesn't do anything for Hornady's claims. People need to understand that "6 figure doppler measuring system" is pretty much a marketing phrase and that it isn't real special. It measure the exact same thing we measure with acoustic's, and that's it.
I'm one of those people who come here to learn. Why don't you provide that further context in your own thread instead of mucking up this one?
Because this is the topic we are talking about in this thread. We aren't "mucking up" this thread, just providing information about the same topic.
BergerFan222
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But all of that is beside the point. Our data with our system is already pretty much as accurate as with the doppler. The difference, and what is being claimed by Hornady, is that they are getting data from the radar to use in their "4th DOF" which calculates spin drift and aerodynamic jump. This is false because the data required for those calculations can not be derived from the radar data.
Hornady's tech document says their 4 DOF solver is using the modified point mass (MPM) method.
The BRL paper in the link explains that the parameters for using the MPM method can, in fact, be determined from radar data. Since BRL has worked out a method for doing it and has been doing it since 1990, I'm not sure why you are saying it is impossible.
http://www.dtic.mil/dtic/tr/fulltext/u2/a229514.pdf
See the introduction on page 1.
Hornady's tech document says their 4 DOF solver is using the modified point mass (MPM) method.
The BRL paper in the link explains that the parameters for using the MPM method can, in fact, be determined from radar data. Since BRL has worked out a method for doing it and has been doing it since 1990, I'm not sure why you are saying it is impossible.
http://www.dtic.mil/dtic/tr/fulltext/u2/a229514.pdf
See the introduction on page 1.
It says they were trying to fit a trajectory to radar data. Doppler Radar provided them with velocity decay data that they then took and tried to replicate using the MPM.
What we are talking about are the coefficients needed to calculate the Aerodynamic jump and spin drift. Those are not derived from radar data.
BergerFan222
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It says they were trying to fit a trajectory to radar data. Doppler Radar provided them with velocity decay data that they then took and tried to replicate using the MPM.
What we are talking about are the coefficients needed to calculate the Aerodynamic jump and spin drift. Those are not derived from radar data.
You are assuming their radar data is limited to velocity vs. distance, when it also includes position and velocity vs. time (the observed trajectory).
The author clearly states in the paper that they have a fitting process that provides all the parameters needed from the radar data to apply the modified point mass (MPM) method.
You are assuming their radar data is limited to velocity vs. distance, when it also includes position and velocity vs. time (the observed trajectory).
The author clearly states in the paper that they have a fitting process that provides all the parameters needed from the radar data to apply the modified point mass (MPM) method.
Please point out where it "clearly" says this. I don't see where it says all of their parameters came from radar data.
You are assuming their radar data is limited to velocity vs. distance, when it also includes position and velocity vs. time (the observed trajectory).
I'm not an expert on this, but to my knowledge Doppler only measures velocity. You can infer (calculate) position because as long as you have velocity data on a time scale, position is simply the first integral. However this would only apply in the x reference, i.e. downrange.
Is their Doppler somehow capable of also measuring y reference? (left to right)
Edit: and in that case, the z reference as well. Not sure Doppler is capable of measuring along more than one axis, which again only yields velocity time-decay...
BergerFan222
Active Member
- Joined
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- 38
I must admit, I too fell for the fancy marketing hype of the 4DOF system. Then, however, I read Bryan's article and saw the fallacy of "4 DOF" solvers from a physics (equations of motion) and simulation background….
There are several scholarly engineering papers and at least one patent that refer to the modified point mass (MPM) computation method as a "4 DOF" technique, so it seems disingenuous to refer to it as a "marketing ploy" or "marketing hype" invented by Hornady. I wonder if the peer-reviewed journals would publish a comment explaining how the authors of those papers are all wrong to describe the MPM technique as having 4 degrees of freedom?
Hornady did not invent the identification of the MPM ballistic method as 4DOF.
Some clarification...
There are many types of modified point mass (MPM) solvers which approximate or neglect various terms for different applications; some are optimized for small arms, some for high angle artillery fire, etc.
It seems that one such MPM model has been referred to as a 4 DOF (this is something I wasn't aware of when I wrote my paper, which will be revised to be consistent with this fact).
The 4 DOF MPM system of equations seems to have been developed for high angle artillery fire where the yaw of repose grows too big to ignore in this application; both in the drift it creates, and the induced drag (the yaw of repose gets pretty big when trajectories arc thru large angles). The lack of fit between traditional PM models and radar data compelled the ballisticians to 'modify' the PM equations to account for the yaw of repose, which allowed for better agreement between the radar data and the model for such high angle artillery fire.
The problem is that this 4 DOF model only calculates yaw of repose, which is enough to get you spin drift, but couldn't calculate aerodynamic jump or limit cycle yaw. Any solver that calculates these additional things requires more than 4 degrees of freedom to do so.
-Bryan
There are many types of modified point mass (MPM) solvers which approximate or neglect various terms for different applications; some are optimized for small arms, some for high angle artillery fire, etc.
It seems that one such MPM model has been referred to as a 4 DOF (this is something I wasn't aware of when I wrote my paper, which will be revised to be consistent with this fact).
The 4 DOF MPM system of equations seems to have been developed for high angle artillery fire where the yaw of repose grows too big to ignore in this application; both in the drift it creates, and the induced drag (the yaw of repose gets pretty big when trajectories arc thru large angles). The lack of fit between traditional PM models and radar data compelled the ballisticians to 'modify' the PM equations to account for the yaw of repose, which allowed for better agreement between the radar data and the model for such high angle artillery fire.
The problem is that this 4 DOF model only calculates yaw of repose, which is enough to get you spin drift, but couldn't calculate aerodynamic jump or limit cycle yaw. Any solver that calculates these additional things requires more than 4 degrees of freedom to do so.
-Bryan
Direct from Hornady: http://www.hornady.com/assets/files/faqs/4DOF-Response.pdf
Hornady Response to Applied Ballistics
Recently the Hornady 4DOF™ Trajectory calculator has been labelled by Applied Ballistics LLC. (AB) as being nothing more than marketing hype, lacking data for predictions and being inaccurately described in its capabilities. Normally we would not respond to internet accusations such as this but because of the standing of AB in the community and possible misunderstanding of what we are doing we feel a response is necessary.
We did not set out to disparage anything that AB or anyone else has done in this industry. They have certainly advanced the understanding and predictive abilities of projectile trajectories in the last 5 years. Just as AB has made strides to advance the science, we too are offering something we feel is another significant step forward in the science and predictive capabilities for small arms ballistics. We are simply trying to advance the science just as everyone else has for decades.
We understand that some of the claims and concepts we are discussing may be foreign, as a 4DOF program has not been previously available to the general shooting public. This technology and predictive methods have been available to the military and defense industry for nearly 40 years. It is proven, validated and mature technology. The 4DOF calculator uses Doppler Radar data to produce high resolution drag coefficient curves for projectiles. Under the right conditions our radar is capable of tracking projectiles above 7mm to well in excess of 2,000 yards. Each projectile has its own unique drag curve. The higher the resolution and fidelity of the drag curve, the better the solution. This is nothing new, however, the use of radar in this industry to produce this drag data is relatively new. Bottom line, the more accurate the measurement of the actual drag of a specific projectile, the more accurate the predicted trajectory.
What is novel about Hornady 4DOF™ is the use of the 4th degree of freedom. This allows for the computation of projectile angle of attack and the associated lift forces on the projectile. This is critical for the accurate calculation of aerodynamic jump, spin drift and to a lesser degree very long range trajectories.
To do this you need to know the mass, inertial and aerodynamic properties of the projectile; we use PRODAS™ software to do this. PRODAS™ is the standard used by most DOD agencies and suppliers when it comes to the design and prediction of projectile aeroballistics. The program has been around for over 40 years. The program operates by using an exact 2D rendering of the projectile along with material properties to accurately determine the mass and inertial properties. This is then combined with predictions of the aerodynamic properties and coefficients by correlating the external aerodynamic shape of the projectile to a very large data base of spark range measurements of similar projectiles.
A spark range is a facility that allows the precise measurement of a projectiles position in space as well as its orientation and angular rate. From this spark range data, precise aerodynamic properties and coefficients are determined for the projectile. PRODAS™ has been validated time and time again over the last forty years by a number of studies by various defense labs with spark range data.
There can be very small errors in some of the coefficient predictions but they are insignificant as it concerns projectile dynamic response and trajectory predictions. In short, we are actually solving analytically the equations of motion and physics of the projectiles flight.
We will be continually adding Hornady and competitors' relevant projectiles to the data base. It is extremely time intensive to generate the projectile files. At this point in time, for typical hunting bullets, we feel any BC based software will provide more than adequate trajectory predictions for their intended use. We will be adding earth based effects soon. This will encompass more than just Coriolis effects. We will also be extending the maximum range of the program to 3,500 meters shortly. App/s will also be coming. We simply wanted to get a working version of the program out there for people to begin to use.
It is our opinion that the proof is in the pudding of any product and is decided by the use of it in real world testing. Merely comparing solutions on a computer establishes nothing, actually shooting the solution will validate the Hornady 4DOF™calculator. We ask that you use the program and give it a fair evaluation before casting judgement on its capabilities. We have expended considerable resources in the development of 4DOF™ and are offering it free of charge as a service to the shooting community.
Hornady Response to Applied Ballistics
Recently the Hornady 4DOF™ Trajectory calculator has been labelled by Applied Ballistics LLC. (AB) as being nothing more than marketing hype, lacking data for predictions and being inaccurately described in its capabilities. Normally we would not respond to internet accusations such as this but because of the standing of AB in the community and possible misunderstanding of what we are doing we feel a response is necessary.
We did not set out to disparage anything that AB or anyone else has done in this industry. They have certainly advanced the understanding and predictive abilities of projectile trajectories in the last 5 years. Just as AB has made strides to advance the science, we too are offering something we feel is another significant step forward in the science and predictive capabilities for small arms ballistics. We are simply trying to advance the science just as everyone else has for decades.
We understand that some of the claims and concepts we are discussing may be foreign, as a 4DOF program has not been previously available to the general shooting public. This technology and predictive methods have been available to the military and defense industry for nearly 40 years. It is proven, validated and mature technology. The 4DOF calculator uses Doppler Radar data to produce high resolution drag coefficient curves for projectiles. Under the right conditions our radar is capable of tracking projectiles above 7mm to well in excess of 2,000 yards. Each projectile has its own unique drag curve. The higher the resolution and fidelity of the drag curve, the better the solution. This is nothing new, however, the use of radar in this industry to produce this drag data is relatively new. Bottom line, the more accurate the measurement of the actual drag of a specific projectile, the more accurate the predicted trajectory.
What is novel about Hornady 4DOF™ is the use of the 4th degree of freedom. This allows for the computation of projectile angle of attack and the associated lift forces on the projectile. This is critical for the accurate calculation of aerodynamic jump, spin drift and to a lesser degree very long range trajectories.
To do this you need to know the mass, inertial and aerodynamic properties of the projectile; we use PRODAS™ software to do this. PRODAS™ is the standard used by most DOD agencies and suppliers when it comes to the design and prediction of projectile aeroballistics. The program has been around for over 40 years. The program operates by using an exact 2D rendering of the projectile along with material properties to accurately determine the mass and inertial properties. This is then combined with predictions of the aerodynamic properties and coefficients by correlating the external aerodynamic shape of the projectile to a very large data base of spark range measurements of similar projectiles.
A spark range is a facility that allows the precise measurement of a projectiles position in space as well as its orientation and angular rate. From this spark range data, precise aerodynamic properties and coefficients are determined for the projectile. PRODAS™ has been validated time and time again over the last forty years by a number of studies by various defense labs with spark range data.
There can be very small errors in some of the coefficient predictions but they are insignificant as it concerns projectile dynamic response and trajectory predictions. In short, we are actually solving analytically the equations of motion and physics of the projectiles flight.
We will be continually adding Hornady and competitors' relevant projectiles to the data base. It is extremely time intensive to generate the projectile files. At this point in time, for typical hunting bullets, we feel any BC based software will provide more than adequate trajectory predictions for their intended use. We will be adding earth based effects soon. This will encompass more than just Coriolis effects. We will also be extending the maximum range of the program to 3,500 meters shortly. App/s will also be coming. We simply wanted to get a working version of the program out there for people to begin to use.
It is our opinion that the proof is in the pudding of any product and is decided by the use of it in real world testing. Merely comparing solutions on a computer establishes nothing, actually shooting the solution will validate the Hornady 4DOF™calculator. We ask that you use the program and give it a fair evaluation before casting judgement on its capabilities. We have expended considerable resources in the development of 4DOF™ and are offering it free of charge as a service to the shooting community.
This is a reasonable reply, but it's buried in the comments section of a campaign in which so many false statements have been made such as:
"... We've raised the bar on calculating trajectories for long range shooters."
and
"... We're changing everything"
and
"We're the first ones to offer a solver that works with drag coefficients instead of BC's"
and
"Hornady's solver is the first to calculate spin drift and aerodynamic jump..."
and the list goes on.
We all welcome advancements in ballistics and LR shooting. But we can all see more clearly if you have the marketing department take about 20% off the hype and claims of being the first and best at something. Stick to the facts. Don't claim things which aren't true in the first place and we can focus on progress rather than having these discussions.
-Bryan
"... We've raised the bar on calculating trajectories for long range shooters."
and
"... We're changing everything"
and
"We're the first ones to offer a solver that works with drag coefficients instead of BC's"
and
"Hornady's solver is the first to calculate spin drift and aerodynamic jump..."
and the list goes on.
We all welcome advancements in ballistics and LR shooting. But we can all see more clearly if you have the marketing department take about 20% off the hype and claims of being the first and best at something. Stick to the facts. Don't claim things which aren't true in the first place and we can focus on progress rather than having these discussions.
-Bryan
Buckammo
Well-Known Member
Nice. A new ballistic program. Unfortunately, the 4DOF prediction for my 143gr. ELD-X starting at 2725fps is wrong by 4.5 MOA (low) at 800 yards. I can shave this down a bit by using their fudge factor. On the other hand I can use JBM or AB and come within 0.5 MOA at 800 and 1000 yards using the measured velocity, the stock G7 BC, and the correct environmentals.
I guess I am old school, I still determine my actual drops in the field and then fit that data to a model for extrapolation and interpolation. It sure is easier when your model is close to the observable.
John
I guess I am old school, I still determine my actual drops in the field and then fit that data to a model for extrapolation and interpolation. It sure is easier when your model is close to the observable.
John
