Dark Brown

The shape is very simple, and doesn't really make use of all the space you have to work with. Your color pallette is very limited, wich doesn't help make your weapon look like magma, and the contrast from one color to the other is really great. Try giving the weapon more volume, use a dark brown for the base color all over the weapon, then maybe add veins or small pools of lava, with a fire-looking gradient. It's a neat concept, but it definitely needs some more work