One tends to watch crazed girl shoot, having loaded round (10)
I believe the answer is:
horologist
'one tends to watch' is the definition.
(person who fixes clocks or watches)
I don't understand how the remainder of the clue works.
(Other definitions for horologist that I've seen before include "Watchmaker" , "Maker of timepieces" , "Clockmaker" , "person behind grandfather" .)