Alright, i've decided on am Acquisition: 1000 Echelon Pattern Mark 3 Assault Stubbers, to be issued one per squad of 10.
This weapon puts out a withering storm of well...Storm fire, and has enough armour penetration to completely ignore common squighide. It's easy to use, and takes a relatively common form of ammo. It's a little heavy, true, but I think being able to put out 1d10+4 I, Pen 3 at RoF 6 Storm outweighs the drawbacks. It's in Into the Storm for those who want a look.