As for firing a gun, whether it be rifle or handgun, I'd be surprised if she didn't knock a tooth out if she was using trial/error. :P
As for weapons and understanding the gravity, I kinda built Benjamin to be a fencer. Rich kid, lots of clubs. All that kinda translates to fencing. So the real question is how will he handle killing someone?
I imagine they would have but the writers probably wanted to scoot the show/manga on a little faster. I thought it was weird that at least Yamamoto wasn't hesitant.
Everyone else kinda showed up with their own...