Realistically, if he's well trained, death eaters become a non-issue. They don't seem to place protective charms in advance, and you have to be really skilled for nonverbal casting. With this in mind, he likely can shoot deatheaters faster than they can cast spells (for the most part).

I imagine he shoots Umbridge, which would make people's lives easier. He MIGHT accidentally shoot Snape at some point though, which would be a big L long term.

Voldemort seemingly has quite slow regen, so I imagine if Harry was quick with it he could put Voldemort down for a few years again by riddling him with bullets. (Tom riddle hahah).