500 is the max for a marksman headshot, you can obtain a higher total kill points for additional combat modifiers but the marksman headshot maxes out at 500 points.
For instance:
The 1st bullet you shoot all game after getting rolled repeatedly kills 2 from the far enough away to get the max marksman pin, both kills being headshots from the m95. The two happen to be the pilot and gunner of a severly damaged blackhawk carrying a full load (pilot, 2 gunners and 2 passengers) all whom are your nemesis' and just killed one of your teammates seconds before... oh and did I mention you are parachuting when the bullet hits? So lets add it up.
50 kill pts x 5 = 250
Headshot x 2 = 20
Marksman Headshot x 2 = 1000
Parachute Kill x 5 = 150
Multikill = 100
Vehicle Destroyed = 100
Avenger Kill x 5 = 250
Avenger Pin x2 = 200
Payback Pin x 5 = 1000
1 bullet, 3070 points
then you could Hypothesize that it got you and your squad the highest score in the game and it took the other teams tickets down to 0. So you could add 200 for best squad and 200 for best player and 100 for a round win on top of any other Insignias/Stars you may have unlocked. Lets say you got your platinum star for the m95 which was your 2nd overall (add 10,000 for the star and 10,000 for Valorous Battlefield Knowledge). Also you got your 500th headshot and 100th Marksman Headshot thats another 10,000 and 5,000 respectively.
So potentially at the end of the game you could have 38,570 points for 1 bullet.
Thats just an example of what noxx_ did last week but he didnt get a screenshot.