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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Hornady 4DOF Ballistic Program
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<blockquote data-quote="Bullseye" data-source="post: 1227630" data-attributes="member: 3351"><p>Let's have a short discussion on how the data acquisition systems in question actually work and make sure there are no misunderstandings or incomplete or misleading information in play.</p><p>Acoustic detectors work by detecting the shock waves signature, crack if you will, from a supersonic projectile. By virtue of the physics in play they are unable to detect or measure anything once the bullet goes subsonic, 1,116 fps at standard sea level conditions.</p><p>The range to which a radar can track a projectile is dependent on a number of things, the power output, the antenna gain, the beam width, the signal to noise ratio (SNR) and very importantly the Radar Cross Section (RCS) of the object it is measuring. The RCS in the case of projectiles, is essentially the diameter of the projectile. The larger the diameter of the projectile the greater distance it can track it. The SNR is a variable that depends on weather, atmospheric conditions and clutter such as leaves on trees, anything that will scatter the radar beam. Under favorable conditions, cold air, no leaves on the trees and a clean range a very low SNR exists and the range of the radar can be extended up to 10%. Firing over a calm lake would be ideal.</p><p>Let's examine the specific case Mr. Litz brings up. They used their acoustic detectors to get a time of flight (TOF) measurement of a .375" diameter projectile at 2,400 yards. That is a significant accomplishment. That's a substantial undertaking that requires some preparation and some good equipment. What they got was one piece of one data point, TOF at 2,400 yards. No velocity measurement, no drag or projectile deceleration data; one TOF measurement. They would have to make some assumptions in order to calculate a retained velocity.</p><p>The alleged, low cost and incapable radar that Hornady uses will measure a .375" projectile to 2,700 yards, give or take a little, under typical conditions. This radar unit is the standard in this industry and has been made by Weibel, TERMA and now infinition, who now owns TERMA, since the early 1980's Under favorable SNR conditions about 3,000 yards. In that 2,700 yards it would gather 650, give or take a few, data points, including 75 to 100 transonic and subsonic data points. For every data point we would have: measured velocity, TOF and distance. We would also have a very high resolution projectile drag and deceleration curve for the projectile. All of this would allow a knowledgeable ballistician to discern a number of things about the performance of the projectile, abnormal drag characteristics, magnus and projectile dynamic instability effects, etc. etc. </p><p>By the way the multi frequency, tracking radars Mr. Litz mentions start in the million dollar price tag range and go up. They need to be either permanently mounted or are put on a large truck. In short, pretty much the domain of government entities or the military. </p><p></p><p>I leave it to the reader to form their own opinion about who is and isn't being misleading.</p><p></p><p>As to Mr. Litz's closing comment I will also leave to reader to form his own opinion about that.</p></blockquote><p></p>
[QUOTE="Bullseye, post: 1227630, member: 3351"] Let’s have a short discussion on how the data acquisition systems in question actually work and make sure there are no misunderstandings or incomplete or misleading information in play. Acoustic detectors work by detecting the shock waves signature, crack if you will, from a supersonic projectile. By virtue of the physics in play they are unable to detect or measure anything once the bullet goes subsonic, 1,116 fps at standard sea level conditions. The range to which a radar can track a projectile is dependent on a number of things, the power output, the antenna gain, the beam width, the signal to noise ratio (SNR) and very importantly the Radar Cross Section (RCS) of the object it is measuring. The RCS in the case of projectiles, is essentially the diameter of the projectile. The larger the diameter of the projectile the greater distance it can track it. The SNR is a variable that depends on weather, atmospheric conditions and clutter such as leaves on trees, anything that will scatter the radar beam. Under favorable conditions, cold air, no leaves on the trees and a clean range a very low SNR exists and the range of the radar can be extended up to 10%. Firing over a calm lake would be ideal. Let’s examine the specific case Mr. Litz brings up. They used their acoustic detectors to get a time of flight (TOF) measurement of a .375” diameter projectile at 2,400 yards. That is a significant accomplishment. That’s a substantial undertaking that requires some preparation and some good equipment. What they got was one piece of one data point, TOF at 2,400 yards. No velocity measurement, no drag or projectile deceleration data; one TOF measurement. They would have to make some assumptions in order to calculate a retained velocity. The alleged, low cost and incapable radar that Hornady uses will measure a .375” projectile to 2,700 yards, give or take a little, under typical conditions. This radar unit is the standard in this industry and has been made by Weibel, TERMA and now infinition, who now owns TERMA, since the early 1980’s Under favorable SNR conditions about 3,000 yards. In that 2,700 yards it would gather 650, give or take a few, data points, including 75 to 100 transonic and subsonic data points. For every data point we would have: measured velocity, TOF and distance. We would also have a very high resolution projectile drag and deceleration curve for the projectile. All of this would allow a knowledgeable ballistician to discern a number of things about the performance of the projectile, abnormal drag characteristics, magnus and projectile dynamic instability effects, etc. etc. By the way the multi frequency, tracking radars Mr. Litz mentions start in the million dollar price tag range and go up. They need to be either permanently mounted or are put on a large truck. In short, pretty much the domain of government entities or the military. I leave it to the reader to form their own opinion about who is and isn’t being misleading. As to Mr. Litz’s closing comment I will also leave to reader to form his own opinion about that. [/QUOTE]
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