I'm currently reading "only in death", a Gaunts Ghosts book. My understanding of a lasgun was that it was an energy based weapon of sorts. In the book, it mentions lasbolts "bouncing and ricocheting" off surfaces, that would suggest mass I assume.
Ok, so what if a lasgun uses some kind of solid ammo? It states that a lasgun ammo clips can be "recharged" by throwing them in a fire (at the expense of the capacity of the clip) in emergency situations.

So....What exactly comes out the muzzle of a lasgun?