Of course there are algorithms to determine how frequently a reward is dropped. (I don't think it's some guy in a cubicle with a bunch of paper slips in a hat). But if you play a game and have 1:1000 chance of getting weapon A (I don't know the frequencies they actually use), if you stick with the same game type it doesn't mean that the next game you have 1:999 chance and the next game 1:998 chance. If you play the same game type for 1000 times it doesn't mean you're guaranteed to get weapon A. Sure, you've got a better chance because you're participating more but each game you've still got the same probabilities of receiving a specific weapon drop. Edit: spelling.