I have this issue as well. Was getting all geared up for a space battle, but alas, won't work with projectile weapons like chain guns. Missiles seemed ok in a few tests I did.
I loaded the latest version of BD armory with KSP 1.12.4 not in multiplayer and the machine guns worked. But I have not tried LMP with BD in orbit with projectile weapons yet.
In my opinion, KSP + BD + LMP is the ultimate game. A physics accurate craft building simulator with multiplayer, realistic damage, and a wide world to interact in... just incredible.
