You were close with the local name, it's mulga, aka King brown. They are actually in the black snake family but are not black to look at. It has something like the third highest volume of venom in snakes worldwide.
The dugite is a different snake, usually known as a dugite down south and gwardar up north. They are in the brown snake family but can be all sorts of colours. The gwardar is the more toxic of the two, but the mulga delivers heaps more venom.
Here's about three feet of a four foot mulga, a decent size but they get to about six, maybe seven?, can't remember. I only read about all this recently thanks to having this one hanging around for a few weeks.