You cant send handles over the internet. Well, you could, but it will most probably fail at some point...
The solution to your problem is the IGNORE_YOU method you originally tried to use
The problem is that the you pointer is probably reset and you havent saved it anywhere, or on the wrong machine.
Here's what I mean:
Create the bullet on the client and attach a custom local function for it.
On the server it runs the function given in the ent_create statement on the client.
With the local function you attached and on the server's function for that bullet, search for the player entity that has the same client_id as the desired client.
When you find it, set 'you' to that player both in the server function and in the local custom function, and use IGNORE_YOU on both machines.
The other method, (I'm currently building it) is to have local bullets only.
Its executed on the client and on the server when a client hits the mouse button. And the same process goes, search for a player entity with the same client_id, set 'you' to that player entity and IGNORE_YOU.
PS.: If you get stuck, PM me. I think I'll have my code working soon...