Probably, I have ignited pyro pellets with musket caps.
777 primers are designed to be "cooler" to help reduce the fouling known as the crud ring, common when shooting 777 with primer ignition.
Blackhorn manufacture says in the directions that you need a hot or magnum primer for Blackhorn 209.
I've had good ignition using standard Winchester 209 shotgun primers w Blackhorn.
Good luck.