It's easily possible. Simple maths would do it, by using the % 'Modulo' (remainder) operator.
Go to System --> Compare two values, then write this:
It means, when the remainder of (shots/10) = 0, then do something. So every multiple of 10 (of shots) it will become true.
Your events will then simply be:
..and so on!
(Note: It will also unexpectedly trigger when shots or kills are 0, because 0%10 is also 0. So just have another condition of shots > 0 to solve that). Let me know if it works.