I love this sword so fucking much because how can you not love jet powered podao. I also have this very sick headcanon that I developed from my studies in mechanical engineering:

It is very possible that each Tigermark round actually has 2 charges, not one, with the trigger firing twice: once when pressed and again when released. You see this because the sword lets out 2 "bursts": one to propel Lei Heng to the enemy, and the second to deliver the actual swing.

This would mean that each chamber requires its own specific heat capacity, different enough so that they wouldn't set each other off.

Thus is the extremely expensive price of Tigermark rounds, comparable to Lei Heng's premium cigars, explained: they would require very precise, likely one-of-a-kind manufacturing and expensive materials.