The top score gets 100 points, 2nd place 99, 3rd 98 etc
If, as often happens, scores are tied then shooters score the same points. For example the winner scores 29 he gets 100 points, two shooters tie for second place so they both get 99, the next placed shooter is actually in 4th so receives 97 points.
If you win you get 100 points (101 - 1 = 100)
If you come in 5th you get 96 points (101 - 5 = 96)
If you scored 61 points then you came in 40th place (101 - 40 = 61)
If you scored 85 points then you came in 16th place (101 - 85 = 16)
There are 10 rounds and only your best 6 scores count. So the maximum total points is 600.
Hope this helps