NOTE: It has come to my attention that a patch HAS moved this solution from Checkpoint 17 of Chapter V to Checkpoint 18 of Chapter V.
I found this easiest to get on Checkpoint
17 18 of Chapter V. When you spawn, wait a few seconds for your Adrenaline Meter to fill, then activate Bullet Time and go to town.
There are four enemies in the first boat, and then six or seven more will pull up behind it. Also, getting six kills, deactivating Bullet Time, activating again, and getting four more kills does not seem to work, I believe they all must come during the same activation.
The achievement will pop as long as you dispatch 10 enemies before running out of Adrenaline, aim does not matter. (I'm horrid at this game and I did it in Free Aim.)
Tips from Commenters!:
Also, any difficulty level or aiming mode works, so feel free to go on Easy with Hard Lock. (Thanks Wyndo and Markyshizzle!)
There may also be a problem if your gun overheats, so try not to let that happen. (Thanks Survivor Seven!)