Cod4 m16 suggestions?

I have been playing mwr for a while just casually. I reached level 56 and I chose to prestige. I am doing this in order to get better and get more headshots. I only want to use m16 even tho mp5 is better in my mind for most because with the m16 if you get headshots you get the kill faster and easier. So currently I'm using m16 with x3 stun stopping power and steady aim. Please make any changes or suggestions you feel necessary.