Well Paulinho, it's simple...just be a cheap dirty b******

especially in Shipment, as you can easily get 50-70+ kills just by camping with an LMG and n00bing it up. The goal is to sit in one of the corners, preferably the one with a broken down car and just let those bullets fly along with some well timed frags at the beginning.
In domination the clock very rarely runs out at 10 minutes and just lasts until one team has 200 points...but in HQ since it's soo hard to capture an HQ in a small map like shipment, most people don't give a hoot and start killing everything on that map, and if you're lucky like I was, you'll have 5-8 people using shotguns running at you from 20 yards away waiting to get picked off by your powerful LMG
Simple.
EDIT:
Also another tip is to die right after you call in a helicopter

I know sounds stupid, but if you do then you have a whole opportunity to get a kill streak going with your helicopter picking off people. And it's hard to take out a copter without getting shot at in Shipment