Why not the GAU-16? It's proven technology and flight rated for the 60H. The HCS squadrons have used them effectively for a number of years and IMO would be the best weapon for the "swarm tactic".
It uses ammo that we already stock (granted, it uses A LOT of ammo) so other than storing more, it shouldn't impact the ships armory as much as having to carry an additional type of ammo.
It is also effective for keeping someone else's head down in a non-permissive environment and will allow our crewman to "miss" with the first couple of hundred rounds, but can walk it in to get the next thousand on target....
I think you mean the GAU-17. I still here proficiency can be a problem. The HCS guys get around it because the Reserves have substantially more ammo in the NCEA than a typical REGNAV Type Wing gets (or advertises, anyway).