"...and consequently be unlikely to hold still in an exposed location for nearly 10 seconds?"
A sniper has a spotter sitting beside him with a high power spotting scope. The projectile would've been subsonic by the time it reached the target, so doubtful that the target would've noticed just another projectile, 0.2" bigger than the other ones being fired at them.
"extreme long range small arms ballistics is a bit of a hit-or-miss affair (ho ho)"
Visit Camp Perry for the National Rifle Matches, and then say that.
Good article! Thanks, Gareth!