It's described in the fluff as an ornately-decorated Boltgun, but honestly, that's boring, so here's what I did:
I stuck the front half of the Sternguard Heavy Bolter onto the back half of the flamer that comes in the new
Tac Squad box, and I like how it looks. It's huge, but not by a totally ridiculous degree, and I'm quite fond of it. It still needs a bit of cleaning up and I'll probably throw some more decorative doodads onto it, but as of right now, I'm fairly pleased.
What have you guys done with yours?