Maybe I'm underestimating what a bunch of slavers with muskets can accomplish, but I think one could sally out and just capture that artillery, no? Would they even understand what kind of fire power they were up against? Think about how poorly the military leadership adapted to technology advancements like machine guns during WWI, and then put that power into the hands of a single mobile soldier instead of a fixed position. I just don't see how that kind of advantage could be overcome.