I don't post to the Hide often, but thought you might find this interesting and possibly useful. I've used Adam MacDonald's Autotrickler and was pleased. I enjoy long range shooting, but find it frustrating trying to spot impacts past 1000-1200 yards, and misses are even worse. MacDonald also has a ShotMarker target system that uses acoustic sensors and uses LoRa to transmit the data back to the shooter. It works very well, and has a marvelous feature that is not promoted. It also calculates the bullet velocity at the target. https://autotrickler.com/pages/shotmarker
The newer generations of "ballistic solvers" are uncannily accurate, especially if they utilize a custom drag profile for the bullet. Historically, these programs used a G1 ballistic coefficient. This compares the bullet in question to an idealized projectile, but G1 is a reasonable approximation for a flat-based traditional hunting bullet. A better fit for the boat-tail bullets is the G7 model. But this is still an approximation and usually becomes much less accurate as the bullet enters transsonic velocities (call this 1050-1300 fps).
From training with Caylen Wojcik, I've become familiar with both Applied Ballistics and the Hornady 4DOF program. Both offer custom drag profiles, where they have used Doppler radar to measure the actual bullet velocity at distance and the "fit" is exceedingly accurate. Both programs allow you to "true" the solutions to your results, but be cautious. You first need to ensure good fundamental marksmanship and that your environmental conditions (especially absolute barometric pressure) are
correctly entered. Hornady uses an "axial form factor" and their technical document explains this (and other details) very well:
https://press.hornady.com/assets/site/hornady/files/ballistic/hornady-4dof-technical-paper-v2.pdf
This truing may be required as the bullet drag can be slightly affected by the type and quality of barrel rifling, muzzle devices and suppressors, and even the choice of powder. In my April class with Caylen Wojcik, we shot steel at 900 yards to evaluate this, and neither myself or my partners needed any correction. It's challenging to do this based on bullet impacts as so many different variables (and the shooter) can affect this. After all, if the bullet strikes are 0.5 MOA high or low, what do you blame?
A month ago I was shooting at 290 yards (they misplaced the 300 yard berm years ago) using the ShotMarker target and my LabRadar. For 24 rounds of 6.5 PRC with the 147gr Hornady ELD-M, the Labradar provided an average muzzle velocity of 3007 fps. The Hornady 4DOF app predicted a target velocity of 2656 fps. ShotMarker reported 2644 fps, so a difference of 12 fps. I've found this well within the "error bars" when comparing my LabRadar to a Magnetospeed (and I tend to trust the Magnetospeed more). I plan to set up at 100 yards and run both the Magnetospeed and Labradar, and use the ShotMarker for target velocity. That should better pin this down, but clearly the ShotMarker must be pretty accurate.
That brings me to last week. I went out to the desert near Boise and put up steel at 550 and 1050 yards and the ShotMarker at 1550 yards. I was using dope from Hornady 4DOF corrected for conditions (station pressure of 27.4", temp of 55, etc.). I promptly had center hits at 550 yards and both 4DOF and Applied Ballistics both called for the same elevation of 2.4 mils.
The 1050 yard target cost me one miss for insufficient windage, but I then had a nice center group visible on this freshly-painted steel. 4DOF called for 6.8 mils elevation and AB called for 6.7 mils. Dandy--I'm not cocky about 0.1 mils even on my good days! (0.1 mils translates to 0.36 MOA).
Things were more interesting at 1550 yards on the ShotMarker. I had two shots off to the right of the target (but ShotMarker actually clued me in to this!) and then put 12 rounds into the target. I did need about 0.3 more mils of elevation than 4DOF predicted. Where this gets interesting is looking at bullet velocity at 1550 yards. For the twelve rounds in the group, ShotMarker reported 1218 fps average velocity. The Hornady 4DOF predicted 1259 fps and called for 13.5 mils elevation. But Applied
Ballistics with the same environment and using Litz's custom drag profile for the Hornady 147ELD predicted 1367 fps and just 12.9 mils elevation. (Happily, I was using 4DOF). See attached JPG of three ShotMarker screen displays.
I got home and looked over this data. Going to the Hornady 4DOF website, I adjusted the axial form factor to 1.02 (a small adjustment according to their technical notes) and this correction provides a target velocity of 1222 fps (measured at 1218) and an elevation of 13.8 mils (consistent with what was required). This would seem to be a more accurate way of "truing" a ballistic solver since it derives from a measured bullet velocity which should only be affected by the rifle/muzzle itself, the drag curve, and environmental conditions. It avoids shooter aiming error, Coriolis, aerodynamic jump, and the like. In a previous email, Adam MacDonald suggested not going below a target velocity of 1200 fps, since at very near the speed of sound the shock wave from the bullet (which is what is detected by the acoustic sensors) is relatively "flat" and measured less accurately that the "cone shaped" shock waves at higher bullet velocities. This ballistic truing process is typically described using target impact location. I'd never considered target velocity before since how in the heck was I going to set up a chronograph at 900 yards and get readings?
The "chronograph" feature of ShotMarker would also make it pretty easy to derive a G7 BC for a new bullet and confirm this at multiple distances. I am finding it to be a convenient and versatile target system. (I have two target frames: one made from plywood and about 2'x3' that I use out to 500 yards, and a second made from metal that is about 8'x8' for long range. He sells spare magnetic sensor mounts that can be left on the frame making it easy to move sensors.) When shooting prone and slung with an M1 Garand, it is a blessing to be able to see shots on target without wiggling over to a scope, and I find the system far easier to utilize than a target camera. But the ability to know bullet velocity at target distance is wonderful and a superb way to "true" Hornady 4DOF.
The newer generations of "ballistic solvers" are uncannily accurate, especially if they utilize a custom drag profile for the bullet. Historically, these programs used a G1 ballistic coefficient. This compares the bullet in question to an idealized projectile, but G1 is a reasonable approximation for a flat-based traditional hunting bullet. A better fit for the boat-tail bullets is the G7 model. But this is still an approximation and usually becomes much less accurate as the bullet enters transsonic velocities (call this 1050-1300 fps).
From training with Caylen Wojcik, I've become familiar with both Applied Ballistics and the Hornady 4DOF program. Both offer custom drag profiles, where they have used Doppler radar to measure the actual bullet velocity at distance and the "fit" is exceedingly accurate. Both programs allow you to "true" the solutions to your results, but be cautious. You first need to ensure good fundamental marksmanship and that your environmental conditions (especially absolute barometric pressure) are
correctly entered. Hornady uses an "axial form factor" and their technical document explains this (and other details) very well:
https://press.hornady.com/assets/site/hornady/files/ballistic/hornady-4dof-technical-paper-v2.pdf
This truing may be required as the bullet drag can be slightly affected by the type and quality of barrel rifling, muzzle devices and suppressors, and even the choice of powder. In my April class with Caylen Wojcik, we shot steel at 900 yards to evaluate this, and neither myself or my partners needed any correction. It's challenging to do this based on bullet impacts as so many different variables (and the shooter) can affect this. After all, if the bullet strikes are 0.5 MOA high or low, what do you blame?
A month ago I was shooting at 290 yards (they misplaced the 300 yard berm years ago) using the ShotMarker target and my LabRadar. For 24 rounds of 6.5 PRC with the 147gr Hornady ELD-M, the Labradar provided an average muzzle velocity of 3007 fps. The Hornady 4DOF app predicted a target velocity of 2656 fps. ShotMarker reported 2644 fps, so a difference of 12 fps. I've found this well within the "error bars" when comparing my LabRadar to a Magnetospeed (and I tend to trust the Magnetospeed more). I plan to set up at 100 yards and run both the Magnetospeed and Labradar, and use the ShotMarker for target velocity. That should better pin this down, but clearly the ShotMarker must be pretty accurate.
That brings me to last week. I went out to the desert near Boise and put up steel at 550 and 1050 yards and the ShotMarker at 1550 yards. I was using dope from Hornady 4DOF corrected for conditions (station pressure of 27.4", temp of 55, etc.). I promptly had center hits at 550 yards and both 4DOF and Applied Ballistics both called for the same elevation of 2.4 mils.
The 1050 yard target cost me one miss for insufficient windage, but I then had a nice center group visible on this freshly-painted steel. 4DOF called for 6.8 mils elevation and AB called for 6.7 mils. Dandy--I'm not cocky about 0.1 mils even on my good days! (0.1 mils translates to 0.36 MOA).
Things were more interesting at 1550 yards on the ShotMarker. I had two shots off to the right of the target (but ShotMarker actually clued me in to this!) and then put 12 rounds into the target. I did need about 0.3 more mils of elevation than 4DOF predicted. Where this gets interesting is looking at bullet velocity at 1550 yards. For the twelve rounds in the group, ShotMarker reported 1218 fps average velocity. The Hornady 4DOF predicted 1259 fps and called for 13.5 mils elevation. But Applied
Ballistics with the same environment and using Litz's custom drag profile for the Hornady 147ELD predicted 1367 fps and just 12.9 mils elevation. (Happily, I was using 4DOF). See attached JPG of three ShotMarker screen displays.
I got home and looked over this data. Going to the Hornady 4DOF website, I adjusted the axial form factor to 1.02 (a small adjustment according to their technical notes) and this correction provides a target velocity of 1222 fps (measured at 1218) and an elevation of 13.8 mils (consistent with what was required). This would seem to be a more accurate way of "truing" a ballistic solver since it derives from a measured bullet velocity which should only be affected by the rifle/muzzle itself, the drag curve, and environmental conditions. It avoids shooter aiming error, Coriolis, aerodynamic jump, and the like. In a previous email, Adam MacDonald suggested not going below a target velocity of 1200 fps, since at very near the speed of sound the shock wave from the bullet (which is what is detected by the acoustic sensors) is relatively "flat" and measured less accurately that the "cone shaped" shock waves at higher bullet velocities. This ballistic truing process is typically described using target impact location. I'd never considered target velocity before since how in the heck was I going to set up a chronograph at 900 yards and get readings?
The "chronograph" feature of ShotMarker would also make it pretty easy to derive a G7 BC for a new bullet and confirm this at multiple distances. I am finding it to be a convenient and versatile target system. (I have two target frames: one made from plywood and about 2'x3' that I use out to 500 yards, and a second made from metal that is about 8'x8' for long range. He sells spare magnetic sensor mounts that can be left on the frame making it easy to move sensors.) When shooting prone and slung with an M1 Garand, it is a blessing to be able to see shots on target without wiggling over to a scope, and I find the system far easier to utilize than a target camera. But the ability to know bullet velocity at target distance is wonderful and a superb way to "true" Hornady 4DOF.
