In my opinion, the single most bad - a$$ weapon on any battlefield, bar none, is the unrealistically large rotary cannon.
However, we only have stats for minifig-sized miniguns. Originally I just treated each barrel of the gun like an independent gyro rifle, but this became so tedious that I made some stats for larger weapons:
Range 8", use 4, damage 1D6+1, fire cone 15 degrees/2-finger cone, 10CP (this is essentially the man-portable version, mounted on a vehicle)
Range 12", use 4, damage 2D6+2, fire cone 15 degrees/2-finger cone, 20CP
Range 16", use 5, damage 2D6+2, fire cone 30 degrees/3-finger cone, 30CP
Range 20", use 5, damage 3D6+3, fire cone 30 degrees/3-finger cone, 60CP
Range 20", use 6, damage 3D6+3, fire cone 45 degrees/3-finger cone, 120CP
Just one random act of violence can brighten your day. Especially if it involves explosives.