If you immediately sprint towards the gun as soon as the level starts and run up a little bit in the open area and then straight back down it delays the floater zombies slightly, just barely enough to reach the gun and shoot them before they kill you. Good luck with this one and the rest of the levels you’ve got left, and thanks man! I think there’s room for a deputy! ;)
I do not understand how you're getting under 10 here, but who am I to question the captain? Congrats on the fourth game you've been champion in, that's truly crazy!