PS4 Resident Evil 5 Mercenaries United Solo Public Assembly Barry 150 kills

so after i just got a 150 kills with barry in prison, i asked myself why i couldn't get 150 kills in public assembly? i think the main reason was i ran out of time because there are only 8 bonus timers. it could be done if you can aim-one head shot- headbutt melee. since my aiming isn't all that great. so changed the strategy , and whoala. i did it!