I need 3 more people
all you need is a second controller signed in as a guest (if you don't have a second controller, just hold the ps button and reassign to controller 2, then just log in to a guest and switch back)
When the gun game starts, just kill your local until you get to the crossbow (just to be sure) and then just knife your local until everyone gets the nuclear medal. then either back out or finish the game

if you're interested in joining me add my psn:SirHermos