Originally Posted by
MaltonNecromancer
The second is a grenade launcher. Image is of Delphan Gruss, from the old "Inquisitor" game (the Gary Morley sculpt looks little like the picture, but *does* carry the gun. It was a grenade launcher in game.)
The other guns have never had an official clarification. Given that they've got rotary barrels, I would say that they were Guns That John Blanche thought Looked Cool, rather than any official 40K weapon. Equipping an entire army with infantry-carried rotary miniguns is fruity as all hell, and so well in keeping with John Blanche's style.
What they are depends entirely on how high power you want to count Skitarri as being when you invent rules for them, I suppose. Make them assault cannons, and the army quickly becomes ridiculous, both in fluff and rules terms. It's more probably they're just some ridiculous autogun or multilaser variant. In Dark Heresy or some other RPG, they'd have slightly modified stats, but in the simpler world of 40K, you're probably looking at either lasgun or boltgun stats. Maybe hotshot lasguns at a pinch.