This game is bit tricky to configure mouse sensitivity correctly and to do that while the party is running make all players mad.
I suggest Devs to provide and offline game room where we could verify and configure correctly mouse and controls sensitivity with various scopes without the need to start a match.

you can convert a mouse sensitivity from another game to sandstorm. you just need to know the dpi and ingame sensitivity mouse-sensitivity.com

I hope for an option where you could instantly start a solo game where you start off in a shooting range.

Perhaps you're in a room with a large cache of weapons behind you.

In this special room, you can use PAGEUP/PAGEDOWN to adjust your mouse sensitivity in real time. Clay pigeons be flying through the air up ahead, you can shoot those to test your sensitivity settings.

Believe me that I wasn't tried the "Local Play" yet!
The local play is good play to config the game but a shooting rang with moveable target is always a good idea anyway!