Yeah, the fusion cannon can get some insane damage, I had a q152 fusion cannon with Specced Heavy Metal, Specced Tricky Trajectory, and Specced High Technicalities, and was able to deal 26k damage on a crit once I was buffed up with all the relevant drugs. For some reason the cannon deals more damage than it should, there must be a hidden damage multiplier or a boost may be applying in a weird way. The cannon also seems to have falloff damage the farther away enemies are from the center of the blast, up to 50% at the very edge.