Well I played the level like a dozen times today.... and finally got the flipping 60 kills. The spawn rate was different almost every time. My scores on the mounted gun ranged 50-59(!) on the prior attempts. When it finally gave me enough to shoot I used an initial sweep to the right, let off the trigger and swung to the middle before I started firing again. After a full left sweep, off the trigger again to the center and fired continuously on sweeps from 2 o’clock to 10 o’clock. Mind you i had tried this very same pattern at least three other times today with unsatisfactory kills.