Using Trap bricks and Explosionshape with the explosion datablock, it could be possible to make an animated 3D sphere that turns around slowly. To do this, give the sphere an animation where it simply spins around slowly, and time it in the game. When creating the trap, give it a firing time equal to the sphere's time used for a complete revolution, clear all the unneeded datablocks related with the muzzle.
To simplify, get rid of all the particle emitters (bullet trails, explosion particles, etc.), set the muzzlespeed to an astronomical level, and it's lifetime to an extremely small level (High speed, small life, so it collapses into an explosion just a short distance from the trap brick, and less chance that a passer-by would catch the round and kill the cool sphere projection) and finally, set damage / radius damage and impulseforce / radius impulse force to 0, and add the following to the ProjectileData datablock:
explodeondeath = true;
And there you have it, a constantly spinning 3D shape that can be projected in any direction from the brick.