PS4 Resident Evil 5 Mercenaries United solo Ancient Ruins Rebecca 150 kills

continuing with my 150 kills challenge. 2 weeks after i finished with the village, ancient ruins still bothers me a bit. i still think the map/timers are too far apart and the stage is too large for the extra timers that are available. nonetheless, the flame spray works wonder in multiple melees. i still don' know if there is an easier way to kill the giant majini, such as utilizing the stun gun melee? let me know if you do know such trick (or another way other than just shoot them down)?