BT Cannon

The BT Cannon (BT砲), where the letter "B" stands for "Beta", is a Double Triple setup invented by a Japanese player TCM-β. It uses a good balance of pieces and it looks beautiful. The important foundation is an early I-mino.

Basic Opening
Opening 1

Opening 2

After the Triple
With the remaining hang, you can even stack and transition into a 4-wide combo.

Some more continuations:

BT Cannon C-Spin
The following setup was invented by a Japanese player going by the name 26_nameless. This particular setup is almost always possible, depending on the order of the pieces in the second bag. The setup also has multiple Perfect Clear opportunities that end on the end of the fifth bag, meaning the setup can be made again. There are more ways to use the third and fourth bags than are shown.

IT Base

TLJ Base

BT Cannon C-Spin In-Depth
First Bag

Second Bag

Third Bag

Fourth Bag

Options depending on how the stack looks after 3 bags:

Fifth Bag

Trinity / STSD and 4-Wide Combo Setups are options:

But Perfect Clear is usually better:

displayed PC chances are under the assumption that the first piece of the sixth bag is put on hold, thus not used in the setup

T-Spin Double into Perfect Clear is very likely when T piece comes early in fifth bag:

Setup #1: Setup #2: Setup #3:

Setup #4: Setup #5:

Other Variations

These are less explored setups starting on the fourth bag, but still have similar Perfect Clear chances as the setups outlined above.

PC Continuations Note: For every PC build with horizontal I piece in the top right corner, there's an equivalent build with I piece one row lower (usually splitting the S + Z combination). Also note that all builds of setup #3 are contained in #1 and all builds of setup #4 are contained in #2.

TSM to BT
It is possible to make a BT Cannon without wasting a T piece. Here, a T-Spin Mini Single is used to make the offset hole. In the second bag, T must be held until the third bag. The third bag can be stacked in any way. If T comes early in the third bag, then do a TSD. Below is an example of a 14th row PC setup:

Mid-game BT Cannon
Even though it is hard to spot the opportunities on making a BT Cannon mid-game, it has the same amount of benefit as making a DT Cannon.

Kaidan Alternative

There are many ways to make a mid-game BT Cannon, but the easiest pattern to spot is to look out for pattern similiar to the field shown below.

So basically, aim for a pattern with at least a block on one side of a hole and 3 steps of "staircase" on the other side of the well. Similiar to the base needed to execute the Kaidan technique. See the field below for the comparison between BT Cannon and Kaidan by using the same base (Kaidan on left; BT on right).

Parapet conversion

This form could also be made by converting a Parapet. You could also see BT cannon as just Parapet but with extra steps.