Under Rated Australian 50 cent coins

[Mister T]

Mr T, any idea on the mintages for those or are they likely just mint sport?

Probably mint sport. One sold recently (a 1977) and it was struck on an under-weight planchet I think.
I think three of the 1977 and one of the 1988 are known.

I didn't even know they existed
Are they COA coins ?

Yes, they're coat of arms. I think older McDonald's catalogues had a little write-up but it seems to have gone missing in the last issue.