A double barrel is when we hold a weak hand or nothing and follow up a flop cbet with a turn bet. The purpose of the double barrel is to get folds on the turn.
When considering a double barrel the flop texture is very important, we want to use flops that our opponent cannot hold that many strong hands on and on flops where there are going to be alot of overcards on the turn that hit our range. A classic double barrel flop would be a flop like:
842 OR 952
On these flops there are hardly any draws at all and pairs that would call a flop bet are likely to be overcarded on the turn. On the flops above we are trying to bet off hands like: 89, 45 or 77.
We can use cards like the following to barrel our opponents off these hands and these can be broken down by grading them as follows:
A: Very good double barrel card, these include cards like: A, K, Q
B: Profitable barrel cards against most opponents, but these do not fit as well with our opening and continuing ranges, include cards like: J, 10
With this in mind turn cards that pair the board on these pretty dry flop textures, are awful cards to double barrel on profitably. Also flops with draws on might be ok to double barrel on depending on our opponents tendencies. However, if we are against a player who will call the turn with draws we should be prepared to triple barrel the river!