Double and triple barreling is the process of continuing a bluff or semi-bluff after the flop. For instance, you missed the flop and continuation bet. The turn is still blank for you, but you believe your opponent will fold if you bet, so you fire another bet (bullet) out there, or double barrel. This concept is something butchered by a lot of bad regular players. Many players are too aggressive in the wrong spots and not aggressive enough in other spots. So let's take a look at when it might be good and when it's bad to keep firing at a pot.
In most spots, the best double barrel card is always an over card to the highest card on board. The theory behind this is very simple. When an over card to the board comes on the turn and you bet it, your perceived range gets stronger and your opponents range usually weakens. This is because flop calling ranges tend to be top pair, middle pair or a weak draw since strong hands tend to get raised on the flop. This is not always the case depending on board texture. For example, dry boards will often have see strong hands being slow played more often. However, you will frequently get folds from almost all hands that werenít at least top pair on the flop. It's important to know your opponent. Some villains are perpetual non-believers. Against these players either bring multiple barrels to the gunfight or donít continuation bet at all.
The worst double barrel card is usually a card that pairs the board. On a T 7 2 rainbow flop, the worst double barrel card would be a T 7 2. With an emphasis on the T. The best barrel card is any card J or higher. This is generally because when the board pairs, that makes it very unlikely that you improved your hand. If you had over cards or a draw of some sort, they know your hand was not improved. It is also less likely that you had that card (that paired) in your hand, since that would mean 3 of the 4 in the deck are now out (obviously not impossible but less likely).
Other good spots to fire a second barrel is when the first card is pretty high and then the second card is also pretty high. So for example you have a K 9 4 flop and the turn comes any card above a 9. Why is this? you will frequently get folds from 9x, mid pairs and ace high floats, which will be a large portion of the villains flat calling range compared to Kx and sets.
There are other spots where you can fire a 2nd barrel when you think your opponents range is weak but will call a second barrel and fold to a 3rd. You can only bet the turn here if you are going to bet the river. One example of this is when you think your opponent has turned equity but doesnít want to raise their hand. For instance if their bottom or middle pair turns a straight draw or a gut shot. They might call again in this case since they now have added equity but their hand is still very weak and will always fold to a 3rd barrel. Also, the equity they get is fairly obvious and when they hit the river will usually bring 4 to a straight. An example of this is if the flop comes out 9 T K and the turn is an 8. All of their mid-value hands, such as J9, TJ, QT, KJ, 79s, and T7s, will call the turn because they feel like they have added equity but will almost always fold the river if it blanks.
Against good hand readers these second barrels will look obvious. However, the fact of the matter is that in these spots your range will be improving with the turn over cards and it puts them in a tough spot when you have the threat of calling a big river bluff. A lot of the time, regulars will think, "Ok this looks obvious," but will still fold because they think they will have to fold the river or make a hero call, which leads to lots of variance. As you start getting called lighter you obviously have to start betting more for value and less as a bluff.
So for example you have pocket Jacks on T62 flop. If the turn comes a K you can often bet for value. If the river comes a Q, you can bet for value again and get looked up by Tx or something like pocket 8′s. Inversely, if you have QJ in that spot and turn a straight draw, you can bet the K turn, and value bet the Q river. It really is a beautiful thing. Remember, when you hit a turn or river over card bet them for value. Donít get scared now, especially if you're going to be betting that spot as a bluff anyway.
As you move higher (about $1/2 and above) you will meet players who know all the moves so this is where some leveling comes in. You may want to bet bad 2nd barrel cards because they will think you shouldnít be barreling there as a bluff and then think your strong. You donít want to level yourself though, thatís important. These players are not the majority. And if you do want to bluff in bad double barrel spots because you will frequently have value hands, do so a minority of the time, so your hand range is still weighted towards value hands.
An example of this is we have a K 7 3 flop, the turn brings a 7 and you continue to barrel. In this spot you will get a lot of folds from pocket 5′s-Qís maybe even sometimes a weak Kx or any draws on the board because villain will assume you are never bluffing in this spot, because of course, thatís a bad double barrel card. So against these good hand readers, a bad double barrel card can sometimes become a good one.