Its a normal coin which has been rounded off, looks quite worn and the colour looks more silver too. I would not be surprised if someone was making and selling these as "round 50c" without making any claims about the year or silver content. I found it in a chubb roll today. I will try to post a pic tomorrow.
Sorry the photo is not so good. Was distracted and not able to do a better photo. Comparing the 2, it has been rounded, is a "flatter" silver colour than the more "chrome" normal coin, and the coin has been slightly mishapen which makes it seem thicker than normal.
I knew what you meant that's why I was so eager to see it. It is actually better than I thought it would look. Still not good enough to pass of on eBay as a round 50c but with a bit more rounding they probably could have.