Load up chapter 1. Make sure the difficulty is set on easy. Playthrough the chapter; once you've run through the mini-mall, you'll come to an outdoor market where 2 cars will pull up and about 8 men will get out and shoot at you.
Run over and stand somewhat close to them. Most of them will be in cover, so they won't bombard you with bullets and kill you. Once you're down, kill 5 of them. Also it helps to have the mac10 looking gun with full ammo. This makes it easier to just spray and pray.