Level 2 Bitanti Village. Check the video below for the whole run from start to finish in 6 minutes - including loading time. Use this route on the easiest difficulty. I made this viedeo for other achievements, but with this route you can get this achievement easy. Be careful, because I missed the jump from the balcony/roof, so my health went down to 1, so I USED MEDKIT/BANDAGE in the video.
Do not use Medkit/bandage for the achievement!
Yo can go as slow as you want and kill as many enemy as you want (but if you hurry and use rifle only like me, get more points at the end, which is good for progress in another two achievements).
If you use only the rifle, you get an other achievement for it (My Rifle is My Best Friend).
I got 9.000 XP points. because the challenges (You can get challanges only if the mission is finished at least 1 time). With the save at the door, you can reload over and over again to get the XP (Jarhead/Veteran achievement > Rank 50 > 1.000.000 XP).
Xbox.com link: https://t.co/PAVFW5XUv3