Originally Posted by
JPDM
"I'd be reticent to pay double in order to lock in a sleeper if I could be reasonably certain that sleepers would be available at the station stop."
That's the point, you can't be certain. As there was 4 of us, we paid up. It is quite cheap in the end in any case. From this experience. I learned to book ahead.
I checked out the OP's route, and 100% agree that he should buy Qiqihar originating tickets in order to eliminate the shear possibility of being forced to endure the hard seat drill.