Is it possible to make a jetpack as a gun, like for jetpackless units you just buy it and have it use it?

Yeah, kinda. It works differently than a jetpack, though. Basically it's reverse recoil that pulls you in the direction you aim.

See the AAL snake mod; he's got a propulsion device alongside his jump jetpack.

Yes i have that mod, hmm ima start working on that sep mine will make it look like hes flying by farting .

just btw, numgun already made a farting gun. Don't think it makes you move though... very much that is.