There is nothing like doubling if you want to double your coins the you need to work hard on it and make efforts so that you can double it in long run.
Actually there is an easy way to doubling your bitcoins but it's very risky because you can also easily lose all your bitcoins by this method. It called gambling, high risk high return.
Don't you think trading would be better than that for doubling the amount in some time sure more than gambling but atleast less riskier than it.