Pick the last level of Venice "Veni, Vidi, Vici" now the idea is to crash through the exit barrier with a combo of x15 (maximum possible for this level) and kill all 10 enemies with less than 50 bullets (use the pistol) and you will get both achievements.

1. Walk around the corner and shoot the guy next to the flaming barrel
2. Turn left and shoot the skullshot
3. turn around and shoot 1 of the guys behind the sandbag
4. Shoot the guy next to the 1 you just shot
5. Shoot Skull shot above arrow pointing right
6. At the end of this corridor is an enemy who appears from the right
7. Just past the last enemy run down the 1st set of steps and turn left and shoot skull
8. Turn around and shoot enemy
9. Shoot skull shot above doorway heading down
10.Shoot enemy that appears around the corner
11.Shoot shield guy
12.Shoot Skull at the top of the stairs
13.At top of the stairs turn right and shoot guy behind sandbags
14.When you enter this area and turn left shoot the bonus enemy who runs behind the turret gun on the upper level
15.Shoot the last enemy and run for the exit

Here is a video of this method: