A legbar rooster over a BCM hen does not produce sex-linked chicks. The rooster will pass the barring gene to all of his offspring regardless of their gender.
Of course my legbar rooster was defective and only had one barring gene. Even in that situation, he could still produce both male and female barred chicks.
If you want sex linked chicks, the hen has to be barred and the rooster must be non-barred.