Spawn an armed Blackfish in editor with the player as pilot. Spawn a fair amount of CSAT forces somewhere to the left of the Blackfish on the same level surface. (an airfield would work well for this) Allow the left door gunner to unload some rounds at the enemy with the 20 mm. Switch yourself as the pilot to the left door gunner's seat and use the 20 mm minigun yourself and listen to the different sound effect.