Projectile replication and networking discuss

I assumed multicast would sim it on the client too resulting in a double instance on the client. but i looked at the code again and the proxy role seems to prevent that. it does seem like some desync could occur with the client having this much authority. I mean. even if the server has authority over character movement there is still some leeway in client interp of character location, or perhaps when client fire while desynced, which could result in a client not matching a sim in this instance. or am i missing something?