Question about Uncharted 2: Steel Fist

Hi everyone. As I've said in some of my posts, I'm trying to get all trophies for this game and I've been having trouble getting steel fist kills (when you need to weaken enemies and then kill them with a single melee attack). So basically my question is: how many times do I need to shoot an oponent before being able to kill it in a single melee hit?

Thanks in advance!

Probably the best way is to go to the level The Dig on Very Easy, buy an M4, then just

1) Shoot them once (or twice, I don't remember- just keep it consistent and keep doing it)

2) Punch them right after.

Avoid headshots, and if someone doesn't dies after the shot(s) and the punch, ignore him and move on to someone else. I got it on my first try.

On chapter 4 on either very easy or easy use the pistol to shoot the enemy one time without using L1 then hit them. It is easy.