Sorry it’s taken so long to reply.
The ratchet ring retaining the mag sprocket is right hand threaded
to remove it you need to drive it using the sloping flanks of the teeth.
I have made a tool from an old ratchet welded to a lever. A bolt
passes through this assembly, the drum and a strap across at the
rear. A nut holds the assembly together. This allows you to unscrew
the ring. Only finger tighten the nut to allow the thread to move. The
notches in the ratchet are for a tool/’C’ spanner but I think you would
be lucky if it worked as they are usually up very tight.
Hope this helps.