The average velocity of any round over 780 feet would need to be ~1,815 ft/s to be consistent with a snick-boom delay of .22.
What is the average of this round over 780 feet? Since it starts at 2,635 ft/s and terminates at ~2,1150 ft/s at 250 yards, the average velocity would be around 2,390 ft/s … too fast to be consistent with a .22 snick-boom delay.
For speed of sound, 780 = VT = 1200T implies T =.65
For this round, 780 = V(T-delay) = 2,390(.65-delay) implies delay = .3236, more than the .22 observed.