I have done that achievement a total of six times, and it only gets easier. Utilize the G2A2 Assault Rifle as much as possible, great accuracy, rate of fire, and power. Also use the ammo glitch. For example, say you have a G2A2 with 1 clip left and you just killed many replicas with the same gun, go around and individually pick up and drop each one, and then you go and pick them all up. Instead of getting 33% of that ammo, you will get 100% back.
Last edited by MUSTANGS 4 L1FE; 03-25-2012 at 04:14 AM.