Step 1: go to the 6v6 or rumble playlist you enjoy the most. People will recommend different ones but in the end you need to be in the game mode your most comfortable with. Step 2: play the match like you would normally if you weren't trying to do the quest. Go for your precision kills but don't make that your sole focus. If your trying desperately to do it it will make it harder, you'll make more mistakes, die more and end up getting frustrated. Step 3: relax and just enjoy the match. If your relaxed you will find it much easier and will get it eventually. I was really focused on trying to get the kills and like you kept getting stuck on 5 or 6. I realised that by trying to hard to do it I was actually playing terribly and finishing matches with horrendous stats because I wasn't actually thinking about what I was doing in each engagement, just trying desperately to get those precision kills. As soon as I chilled out about it and played normally I nailed it straight away. One important thing to note is that you will find it hard to do in any match where one team is much better than the other as you will likely run out of time too soon. Once you get a nice balanced match though it will be easier.