I can help you start, but ive never fully achieved the bouncing around the room part.
First off, you'll need the said weapon to be labeled, "grenade", like so:
Then give it a salvo count of 5 or something, and a nice spread so that its not all a clump when you shoot it.
secondly, in the ordanance file, (labeled "shell"), play around with these lines:
velocity is the speed intensity essentially, and gravity basically defines whether it will go up or down once its in the air.
I know theres a line telling the shell (grenades) to bounce off objects, that would go in your ord file, but i dont know of one that tells it to bounce off the terrain as well. Hope this helps