Let it not be said that the Space Marine weapon techs sat on their hands and didn't work at coming up with all sorts of weapons with which the armies of the Emperor could bring all sorts of death upon the enemies of Mankind. Forge World has a whole bunch of new heavy weapons with which you can outfit your models.
Heavy Bolters, and Plasma Cannons, and Multi-Metlas! Oh my! There's also the Leviathan Cyclone Melta Lance for your dreadnaughts. I don't know what that does, exactly, but it sounds like the hot winds that would blow across the plain in Kansas during the summer.
All of these are available to order now.