So it's almost 10 years later, and I found this topic searching for anyone else with 1966 50 cent error coins.
That is a nice planchet flaw you have shown. Apparently, 50 cent errors are as rare as rocking horse poo.

My father had a keen eye for errors back in the day, and amongst his collection were 30 x round 50's. 9 have errors, mostly minor delam / cracks, one with a small
Cud, one with a fine die crack, and 3 with some significant cracking and delamination.
Apologies up front for the pics, still finding my way.
Heres the first, when time permits I'll post the others.
This one has a flaw starting in the roo leg, making it's way up through the shield wreath and star to the rim.
It also has a tiny strike through on the obverse, but pretty insignificant.
Cheers ttkoo





The Ox moves slowly, but the Earth is patient.