The bombs carried by a Gyrobomber consist of metal spheres filled with gunpowder. Before he drops a bomb the Dwarf pilot must light the fuse. Obviously, flying a Gyrobomber one-handed while lighting and throwing a hissing, spluttering bomb with the other puts some constraints on the pilot's ability to guide the machine.
During the Remaining Moves sub-phase, models with this special rule may drop a bomb unless they are fleeing or have declared a charge that turn. To make a Bombing Run, select one unengaged enemy unit that the Gyrobomber moved over in that turn and place the large 5" template anywhere over the target unit (but note that it cannot cover friendly models) and roll for scatter and damage as for a stone thrower from the Warhammer rulebook. If a misfire is rolled, use thechart below. Grudgebuster bombs have the following profile:
After resolving the damage caused by a Grudgebuster bomb, roll a D6. On a 4+, the bomb scatters D6" from where it first landed (a Hit! result remains in place). Place the small round (3") template on the new location and resolve damage using the profile above. It cannot bounce a third time.