Normal difficulty. Chicago Chopper 1 shots the standard freaks, with penetration, ammo capacity, focus perks and the upgraded mag for the Chopper its pretty easy to kill hordes.
Ah, I think I am'nt quite there yet to that gun. That at least gives me hope of continuing my hard save to the end.
Everything in the above reply is my opinion, from my own perspective and not representative of reality outside of my own head!
-Android user, please be gentle with critique on my spelling.