Exactly how rare are 'Rare Chances'?

[li]I’ve come across these quite a few times in the last week, and just now, while attempting to grind some Foreign Currency, have ended up with the most expensive weapon currently in the game. I’m not arguing against this, but is anyone currently aware of the percentage chance of this, or something similar? Sorry if this topic has been asked before.

it fluctuates based on the ‘rare chance’. some people’s opinions are that it is 1% for the one you are doing, but there’s one card’s rare success that happens so often (if i’m remebering correctly, and in the guest lecture you can actually get the concoction to explode.) that the normal success is more common. it might be another, hidden, shadowy check, or just a 1-in-100 chance. we don’t know for sure, i think.
[/li]