The coolest part about going 12-21 was that every kill was a multi (2+, not 4+ as in the game) kill. I'm not asking to brag about going 12-21 (It was on Invasion, hate that map) but at the bare minum, you have to admit it to be an interesting feat. If I remember correctly:
2 Kills- 1bullet2kills w/Intervention
2 Kills- AUG, two people in same spot, sprayed both and got the points for double kill
I used two classes, my sniping Class, and a heavy assult class
M93 Raffica Extended Mags
SoH, Stopping Power, steady aim
Scavenger, Hardline, Steady Aim
And as a side note, this match's match bonus allowed me to prestige; which was cool.