Infinite Ammo and Grenades
Create a new multiplayer game(Connection doesnt matter as you wont actually be playing). When you get to change the game settings, one of the menus will let you set unlimited ammo. Start the multiplayer game and then quit it, and Load an old game or start a new one and you should have unlimited ammo, as well as unlimited grenades. You only have to do this once each time you start the game