Resident Evil 6 is a cool game,was just playing the demo with a second person thinking about buying it.
You actually need to beat all the campaigns first. Then buy the inf ammo skill and purchase each gun inf ammo also.
its just for the online mode when some one with inf ammo join you and it dont have any thing with achivements
XDDD you dont have infinite ammo when you dont have the skill the option do only activate the skill in the game when you have the skill and have infinite ammo - off then have you no infinite ammo^^