yes this is the exact shot on forums and in youtube from months ago people posted to do, arica harbor sitting bases back shooting people as they spawn. Maybe one day you can do it with a rpg. Then it will be original!
my best is 680 but like i said before i got a 580 headshot + an Avenger kill now i did have another shot that was 2 heashots in 1 for i think it was 380 each + a savior kill and a avenger kill which added up to 740 but the actual marksman headshot was 380 so it wasnt to far.
Yet another one but this time was a bit further back and yet still the same 560 so im thinkin the only way to get past 560 is a avenger kill on that + a savior or something.