Post by xbowhunter on Jan 27, 2023 7:40:26 GMT -8
Hello,
I spent many hours searching for an appropriate value for the G1 drag coefficient setting. ATN tech support was not able to provide this information due to the 4K pro being dedicated to rifle ballistics and not arrows. At first I plugged in various values, not knowing what I was really needing, to find the ballistics were not aligning over distance; spot on at shorter yardages however major poa to poi error at distances. Being the bow is set and performs to 350FPS with a 410 gr arrow the FPS setting was required to be at the optic minimum; 328 fps but the issue of poa to poi error persisted. I finally threw in the towel and researched the ballistic drag equation on the net and began running numbers relative to mass, shape and weight of an arrow. The time was well spent and solved the issue.
Relative to speed/arrow mass I used Excel to build a table for bow speeds along with arrow data to find the 4K really performed well with a setting of .04 to .06. .04 performed perfect for my 350 fps bow whereas .06 was perfect for my other bow shooting 380 fps. I also run numbers for the new tech bows running near 500 fps and found the value calculated to be .1 The faster the bow, the higher the value due to increased drag at increased velocity.
I shot the 350 fps bow from 20 yards, zeroed, and followed with 30,40 and 70 as the long range test distance. The setting of .04 provided .375" max error shooting off a rest at 70 yards. Yes, I do make my own custom arrows that are match grade, spine indexed to achieve this accuracy along with shooting everyday 25-35 times per day. The old saying; aim small, miss small
Although this bow now shoots lights out regardless of yardage, I did find one Bug in the ballistic setup. Both FPS and coefficient settings have a direct affect on the ballistic equation, changing the arrow/bullet weight DOES NOT alter the hold over/ ballistic equation. For example; If my performing setup provided a 10" holdover and I changed the weight of 410 to 100 or to 600, the hold over value never changes. Firmware bug? Not sure. I contacted tech support and the tech found this very interesting and stated he would pass this information along to the code writers.
This discovery made a world of difference in the accuracy and in hopes it helps other crossbow shooters that may experience less than acceptable performance at various yardages.
Have a great day,
Carpe Diem
I spent many hours searching for an appropriate value for the G1 drag coefficient setting. ATN tech support was not able to provide this information due to the 4K pro being dedicated to rifle ballistics and not arrows. At first I plugged in various values, not knowing what I was really needing, to find the ballistics were not aligning over distance; spot on at shorter yardages however major poa to poi error at distances. Being the bow is set and performs to 350FPS with a 410 gr arrow the FPS setting was required to be at the optic minimum; 328 fps but the issue of poa to poi error persisted. I finally threw in the towel and researched the ballistic drag equation on the net and began running numbers relative to mass, shape and weight of an arrow. The time was well spent and solved the issue.
Relative to speed/arrow mass I used Excel to build a table for bow speeds along with arrow data to find the 4K really performed well with a setting of .04 to .06. .04 performed perfect for my 350 fps bow whereas .06 was perfect for my other bow shooting 380 fps. I also run numbers for the new tech bows running near 500 fps and found the value calculated to be .1 The faster the bow, the higher the value due to increased drag at increased velocity.
I shot the 350 fps bow from 20 yards, zeroed, and followed with 30,40 and 70 as the long range test distance. The setting of .04 provided .375" max error shooting off a rest at 70 yards. Yes, I do make my own custom arrows that are match grade, spine indexed to achieve this accuracy along with shooting everyday 25-35 times per day. The old saying; aim small, miss small
Although this bow now shoots lights out regardless of yardage, I did find one Bug in the ballistic setup. Both FPS and coefficient settings have a direct affect on the ballistic equation, changing the arrow/bullet weight DOES NOT alter the hold over/ ballistic equation. For example; If my performing setup provided a 10" holdover and I changed the weight of 410 to 100 or to 600, the hold over value never changes. Firmware bug? Not sure. I contacted tech support and the tech found this very interesting and stated he would pass this information along to the code writers.
This discovery made a world of difference in the accuracy and in hopes it helps other crossbow shooters that may experience less than acceptable performance at various yardages.
Have a great day,
Carpe Diem