According to Robin Walker in a post at Rock Paper Shotgun, the system is bugged, and along with the explanation of how it works, they are planning on fixing it so that the drop rates are more in tune with what they intended. In his own words:
"As in everything else we do, we want to iterate, so this is really the first step towards our desired implementation. We also think we have bugs in the system as well, since we're seeing some players not finding any items after a few hours of play, which is not at all how it's tuned. We want unlockable drops to be a pretty regular occurrence for players, with the cosmetic hats being the rare finds."For those wanting to try out the new Sniper and Spy weapons, this is great news! We'll keep you updated on the status of the new update as well as how the new unlock system works.


