you can't do this to an Australian coin
Actually in my naivety I thought this was some kind of clad coin which had been pulled apart somehow (the inner core removed leaving behind a copper-nickel shell) which definitely cannot be done to an Australian coin. But of course British 10p coin is made using normal copper-nickel planchet.
Oh yeah! Give me a metal lathe and I'll show it can be done!!
David, I hope that's not what you've been doing to those 1966 20 cent coins you've been marking.