i got a quad once just with Steady Aim and Acog (acog is better)
my quad:
[ame="
https://www.youtube.com/watch?v=iiWCdbS1CAQ"]YouTube - Indy1995's Siik Quad Kill!! CallOfDuty4[/ame]
and got once a triple just with acog and steady aim again.
Its when you hit them in there head then you have more change to get a quad/triple then hit them in the legs