I got the badge easily with this combination. Ok, so all you need to do is buy the FN SCAR (which falls under the "Assault Rifles" catagory) then spend the rest on the "Marathon Man" upgrade, Maximum HP and Maximum Base HP. Once those are purchased, just start the level, and just stand there, fighting off the hoard of zombies. If there are too many zombies, go off to the left side of the base and shoot them from there. Hope this helped. Thumbs up this comment?
 "Zening"){kind=icon}
 "Thing-Thing Arena 2"){kind=icon}
 "The Endless Zombie Rampage"){kind=icon}
 "Shore Siege!"){kind=icon}