Sure, he shot a guy in the head point-blank. That wasn't the impressive part of that, it was that he appeared next to the guy in an instant. If you can do that. A knife works just as well.

I think though that most people at the Strawhats level don't have anything to fear from guns unless the gunner doesn't something supernatural. Even if you aren't bulletproof like Luffy, Franky or a Logia user, people like Zoro and Sanji are fast enough to just dodge bullets.

Franky is all the gunslinger the Strawhats need and more.