Doubling Down Blackjack Strategy : According to the doubling down of the blackjack strategy, you can double up เกมสล็อต the primary betting amount. In return, you get the option to call for the additional card as well. Casinos may let you take advantage of either of your hands like soft or hard hand cards. But doubling specifies the hand you should play with a hard hand hitting the numbers 10 and 11.