30 damage isn't really that scary... won't penetrate the front armor of an Atlas anywhere but the head, for instance. But I suppose it's workable anyway. :)
Personally I'd go with the original description of the Volcano cannon (D-laser); a starship main gun. I'd call it a sub-capital laser/3 with a mounting that allows ground-to-ground fire. Keeps your stats, but now the droppers have to watch out! ;D
The game mechanics don't convert perfectly. In EPIC you could kill a light mech with a single medium laser, as long as they fail their armor save. Battletech game rules give more survivability. I'd certainly be afraid of a Super PPC like that. :)
Hopefully this week I'll finish converting over a lot of the standard Imperial tanks. Clearly Titans and superheavies held the most interest for me. I'm not sure that a standard Rhino or Chimera will get any more attention than "tracked APC". Orks, Eldar, Chaos, Tyranids, and Tau all have some interesting stuff I want to look at too, like the Ork Lifta-Droppa, which shoots an anti-gravity beam that actually picks you up and then drops you. :D
