The bulky metal part came from an old Necron metal destroyer, the arm is from a missle launcher marine, the boxy part of the weapon is from a vehicle missile launcher, The box with the line on the side of the missile launcher cam from one of the ammo boxes from a predator that I cut apart and finally the stock of the gun came from a plasma rifle. Throw on somw wires that I actually drilled into the plastic of the weapon and you have my conversion beamer.
The weapon is super fun to use in actual games too.