I am not familiar with using projectiles but yes i would assume you just need to spawn the projectiles on the server making sure the projectile actor is replicated and all clients should see them, since those are spawned into the world that everyone sees. I could be wrong but I don’t think that part needs to be multicast either. I think only the animations, sounds, fx etc. on the weapon itself need to be multicast. Client handles input and like how the fire modes work, then calls to server, run line traces and then spawn projectiles on server, then call multicast where you’d do the animations of the gun.
edit from chat gpt:
Spawn the projectile once on the server and make the projectile actor replicate; don’t use a Multicast to spawn it.