So if it started at 1000fps, it would be down to 520fps by their calculation at 1000 yards.
To get there in 3 seconds, he has to average 1,000 fps. So he has to be going considerably faster at the start.
Guess 2,000 fps.
Your Input Variables
Ballistic Coefficient 0.212 Velocity (ft/s) 2000 Weight (grains) 147
Maximum Range (yds) 1000 Interval (yds) 100 Drag Function G1
Sight Height (inches) 1.5 Shooting Angle (degrees) 0 Zero Range (yds) 100
Wind Speed (mph) 0 Wind Angle (degrees) 90 Altitude (ft) 0
Pressure (hg) 29.53 Temperature (F) 59 Humidity (%) 0.78
Ballistics Results
RANGE (YARDS) VELOCITY (FPS) ENERGY (FT.-LB.) TRAJECTORY (IN) COME UP IN MOA COME UP IN MILS WIND DRIFT (IN) WIND DRIFT IN MOA WIND DRIFT IN MILS
Muzzle 2000 1306 -1.5 0 0 0 0 0
100 1660 900 0 0 0 0 0 0
200 1372 614 -11.3 5.4 1.6 0 0 0
300 1154 435 -41.2 13.1 3.8 0 0 0
400 1018 338 -97.1 23.2 6.7 0 0 0
500 930 283 -186.6 35.6 10.4 0 0 0
600 864 244 -316.4 50.3 14.6 0 0 0
700 809 214 -492.5 67.2 19.5 0 0 0
800 761 189 -722.5 86.2 25.1 0 0 0
900 717 168 -1012.7 107.4 31.2 0 0 0
1000 677 150 -1371.1 130.8 38.1 0 0 0