Gearbox for my airsoft replica

hello,

I have some problems making the gearbox of my airsoft gun project working properly.

I can make the 2 gears interact with each other as they are supposed to, using a width mate constraint, but I can't give boundaries to the movement, and prevent the gears from interfering.

I included a zip with a test assembly I made, I'd like to make this part working properly before continuing with my project.

Thanks in advance.