OMG
it wasn't the goal to jetisson the tubes after firing them.
that's for an emergency case. you'll be always able to fly the plane with a CG slightly moved but you have to trim much more than usual, at least if you have to escape you do not have any draggy "air brakes tubes" slowing you down. Just the same for the BK75 in the HS129, it wasn't the goal to drop it after firing the shells