1RB1RF_1LC1LF_0RE1LD_0LB1LD_---1RC_1RA0RD

1RB1RF_1LC1LF_0RE1LD_0LB1LD_---1RC_1RA0RD (bbch) is an unverified probviously non-halting BB(6) machine found by Racheline on 24 October 2025.

Argument by Racheline:

this one is probviously non-halting i think
basically, the tape length has a parity, which changes every time the bouncer hits both ends at the same time. after the parity changes, the iterated bouncer starts from the left end, roughly doubling in size with each iteration, and when it hits the right end, it moves the right end to fix the parity, *except* if it hits both ends at the same time again, in which case it halts.
assuming that the starting position of the bouncer behaves pseudorandomly and with uniform distribution, the probability of a parity change at a given length should decay linearly with the length, which means the lengths at which the parity changes happen should grow exponentially. for the machine to halt, the length would have to be one of the lengths of the iterated bouncer, and those grow exponentially too. so we need two exponentially growing sequences to intersect, which i think makes it probviously non-halting (unless it gets unlucky and halts early)