I used to use the scoripion way too much, and it was the first gun I really used. I didn't even realize I had 100 headshots and all the bloodthirsties, etc, till I realized what a camo was. By that time, all I needed was the no perks/attachments challenges. Which were easy peasy.
This is what I used and it felt like it helped me out.
Chicom/Silencer/Extended Magazine Ghost Scavenger Dead Silence/Dext C4 EMP
I would find myself completely sneaking up on groups of people(TDM) and just take my time and pop them in the head.
Also something that I think makes this easier is using the EOTech sight with the bling reticule. I don't know what it is about it but I really find it very easy to get headshots with that reticule. --- New Commentary! 4/26/13-http://www.youtube.com/watch?v=ocwjbOH_dA0 GT: Dan Harkinz