Hi Tony:
You have a Canadian made casing. The broad arrow mark was stamped into the brass and the "C" braod arrow is an ink stamping (yours is nice and clear so don't polish it away!
)
The primer is a No15 Mk II/C (the /C is the indication that it is Canadian) made in May 1942. The other numbers are lot numbers and codes for accounting, etc.
People might think it odd that a Canadian casing ended up in Oz but I'm not surprised at all. The Canadian arsenals were pouring out ammunition for the whole Commonwealth... perhaps that one went from Canada to UK to North Africa or the Med and then to Oz... if it could only speak!
Cheers! Mike