Double Barrel

1. A term to describe the act of betting on two consecutive streets without a made hand, typically done within the framework of a continuation bet bluff. In order to execute a double barrel bluff on the turn, you must have made a continuation bet on the flop.
2. An actual double barrel shotgun.

Explained

The act of double barreling is something many novice players grossly misunderstand. You should not, under any circumstance, bet on two streets in a row simply because your opponent checks to you and you think you can make him fold. The double barrel is much more complex than that, and generally must be used less frequently and in the correct spots in order to be effective.

For discussion's sake, let's say you're the preflop aggressor and get called from the blinds. The three most important factors in determining instances to execute a double barrel in this situation are board texture, your opponent's playing style and range, and your own image.

Board Texture: Generally speaking, the best double barrel card is an overcard to the board. The reasoning is that when you bet this card, your perceived range gets stronger and your opponents range becomes weaker, since his calling range on the flop tends to include top pair (which is no longer top pair), middle pair (which is now third pair), or a weak draw. Keep in mind that this range is obviously not always the case - for example a set might just call on extremely dry board - but it's definitely a good place to start ranging your opponent. By the same token, the worst card to double barrel is usually a card that pairs the board, because in essence, it hasn't changed anything and your opponent will likely call another bet.

Opponent's Style/Range: Going hand in hand with determining a good board texture to double barrel is being able to decipher your opponent's playing style and what they are likely to do with their range on certain board textures. A good example of this combination is finding spots vs. opponents who are weak enough to call a turn bet but fold to most river bets. One possible scenario for this would be an opponent who turns a gutshot straight draw to go with their third pair - when an ace peels off on the river you can safely bet and watch them fold.

Your Image: Of course, the relevance of your image depends on who you're playing against - if your opponent is a donkey with no concept of image, then disregard this section, and probably don't even attempt to double barrel bluff them because it won't work. However, against more competent opponents, as long as your timing is right and you aren't constantly doing it, your double barrels in position should work. Good players may be aware of what you're doing, but in most cases they'll have to respect your improving range when that overcard comes on the turn.

Example - When to Double Barrel

It's folded to you on the button and you decide to make a raise with Ks7s. Your opponent in the big blind calls and the flop comes down Qh 8s 4d. It's checked to you and you fire half the pot - your opponent calls. The turn is the beautiful Ac which is a perfect card for you to double barrel. Let's assume QJ is the absolute top of your opponent's flatting range and say that he most likely has a hand that includes an 8, like K8, Q8, T8, 98, 87 - these are all hands that your opponent will have to fold if you represent the ace, and they might even fold a weaker J if you size it right. Again, this might not always be the case, but this is definitely a good spot to double barrel.

Example - When NOT to Double Barrel

The preflop scenario is the same as the above example: you open the button with Ks7s and the player in the big blind calls. However, this time the flop comes down Th 8d 2c. It's checked to you and you fire half the pot, and again your opponent calls. The turn is the 8s, which pairs the board. This is a bad card for you, and certainly one that you do not want to double barrel. The reason is that your opponent is going to call your bet again unless he has absolute air, but assuming he's not crazy, his range most likely includes a T, an 8, or a smaller pair, all of which are hands that are going to get to showdown on a board like this. Just check back and fold to a river bet.