this doesn't belong here: should be transferred to scams,hyips and ponzis section
Or better directly to trashcan.
I've heard that most of BTC doublers are pure scam, and I'm going to test this statement) What is a minimal amount of BTC to invest?
All of them are ponzi scams. The only difference is some scam you with the very first try and some handle to pay you once or twice (depends on how many new depositors coming).