1RB1RA 1LC1RF 1RE1LD 0RD1LB ---0RA 1RZ0LE

1RB1RA_1LC1RF_1RE1LD_0RD1LB_---0RA_1RZ0LE (bbch)

AFAICT this is the current BB6 (with one unused transition) step champion.

1RB1RA_1LC1RF_1RE1LD_0RD1LB_---0RA_1RZ0LE

Steps:    ~10^13.39223  =  24_673_582_891_560
Nonzeros: 2_323_223  =  2_323_223

C(a, b, c) = $ 1^a 0 1^b <C 1^2c+1 $

C(a, b+3, c) -> C(a, b, c+2)

C(a, 0, c) -> C(a+1, 2c+1, 0)
C(a, 1, c) -> C(0, a, c+1)

C(0, 2, c) -> C(1, 2c+4, 0)
C(1, 2, c) -> C(1, 2c+6, 0)
C(2, 2, c) -> C(1, 2c+7, 0)
C(a+3, 2, c) -> 1^a 01^c+3 11 Z>

Start: @2: C(0, 1, 0)

It does one of these interesting Collatz Markov Chains where it only halts if $a\geq 3$ and $b{\bmod {3}}=2$ and otherwise has a couple ways to reset $a\leq 1$. But eventually after flipping that coin 62 times it finally halts.

Analysis by User:sligocki.