Re: metal gong target
I made some really good ones years ago from used discs from a pasture renovator.
The convex shape is great as it makes it all but impossible to punch through them because you won't hit them flat on.
They were 26" Dia and about 5/8 or 3/4" thick anyhow if I remember right.
Scrap yards in a rural/farm area can be your friend. So can welding shops and impliment houses as they will tend to have things like that laying around you can buy for scrap price.
Without the First and Second Amendments the rest of The Constitution is Meaningless.