Gears of War 3 - Private

Private Matches can involve friends or just bots. If you create the match then you're the host and get to set all the rules. You can change who can join, how many rounds to play to, the map you play on and even which weapons appear on the map. Where you don't have players, you can fill the match with as many or as few bots as you want, making this a good place to practice with weapons or just mess around.