Two others solution are great but i want to give you more tips.
I did it on NORMAL, and on the first attempt achievement didn't pop due to... throw a rock
! So to be sure you do it right just avoid puch
Second time i focus on methodical progress and,
i don't want to copy great work other solution authors so i pass to point when you enter to Buggy... do not enter the Buggy - to be precise
Just walk down without any unnecessary speed and head to fallen tree. Across lava and next across rocks.
Then run between shooting guys and climb on hill with radar. Be careful a do not grab Sniper Rifle. Pass through hill and head slightly right, go down, to road.
Jeep with three guys should arrive and crew should leave car. Quick steal vehicle and kiil all you want.
Now the last part.
Ride to the roadblock and kill all enemy (rockets are pretty
). Go to Armory (building on the left and grab armor). Back to Jeep and fire rocket at the final building. Enemy should leave fences and try to kill you - how sad, cause (on NORMAL or EASY) they really easy to kill. Now take a walk to final door. Maybe some enemy still waiting for you(in cover), but with full armor and full sprint bar you may take beer a finish this level with one hand.
Achievement pop !
And if you die, just reload last checkpoint all still will works.
I hope that was hopeful, especially if someone don't like insane runs - like me.
Feel free to comment.
Happy hunting !