If by BCM you mean Black Copper Marans, then that is its own breed and essentially the same as a French Black Copper Marans as Black Copper Marans originated in France. A cross between a Black Copper Marans rooster and a Barred Plymouth Rock hen is a black sex link hybrid, or sometimes called a Dominant Copper, Mystic Marans or Copper Rock depending on the hatchery that sells them.
If your chick has barring it may be a black sex link rooster as only males have barring with that hybrid. Others more knowledgeable with BCMs may provide better insight.