Recoil of any kind is currently not possible beyond _really_ gumby looking off centre rotations of the smaller barrel (ie, you set the centre way away from the gun, and have it rotate backwards and forwards by tiny amounts.) or scripting which will as far as I know break collision detection for at least the turret barrel.
There is a "turret-firing" trigger for submodel animations, but it only works for single part turrets, making it completely useless for turret recoil. Believe me I've tried.
Taylor was working on a 'turret fired' trigger that would work with multipart turrets, but according to mantis he's not anymore.
Added to this is that there appears to be a 5 level of hierarchy practical limit to FS models. Anything above this causes bizzare bugs in of all things the rendering process. Shots look 2d, effects appear and vanish depending on the view cameras angle and stuff like that.