While i have had a bit of time to think this whole thing over, I believe i came to a sound enough conclusion based on some other topics as well.
I have stated elsewhere that the HoP should really not be as engaged in Cargo as he is IF there is a Quartermaster present, and if not really cargo techs can do it all alone... So i only deem it logical for the HoP to both organize and arm the Gateway expeditions. He is the one that grants weapon permits and he is the one in charge of general public so I honestly see no other reason or role in the game that could fit this job any better. Now whether or not the Head of Security is willing to provide arsenal support to the expedition team is another thing, and I will agree that Gateway expeditions should not be forced but rather spontaneous and heavily dependent on the type of round currently being played.