You are forgetting the most simple reason, sample group and history.
Why are there fewer black olympic swimmers?
Someone might prattle off "bone density" or "melanin affecting skin density", but the real reason has been know for quite some time. Due to racial discrimination in the late 1800s and early 1900 (and not to mention slavery before that), black people were not allowed into public swimming pools, and eventually, when legally allowed, it was shunned heavily. As a result there isn't a history of swimming in black culture, so fewer of them do it. Also olympic swimming does require a certain wealthier class of person to get regular access to the pool for training, and there is still a economic divide at the highest levels between white and black athletes.
The same is with shooting, it has been male dominated for so long that there is very little impetuous for girls to get into it growing up. It's a very stereotypical father son bonding thing in the US and other countries, and speaking from my own experience, as a member of the rifle (and archery) clubs in university, it appeals more to men than to women.
So in the end you just have a smaller pool of women in shooting, and thus less chance you'll have olympic level athletes.
But really all this would mean is that if competing together, fewer women will win, but (guessing now) it is quite likely that the proportion of medals won would be somewhat close to the proportion of women active in the sport.