How much tempered steel do I need to stop a 5.56 round?

Question

For a little writing I'm doing. I'm wondering how much armor the hero would need to stop a standard NATO 5.56 round. How about a 7.62?

Answer 1

I know from personal horse play that 3/4 mild steel will stop a 7.62 round, Just a guess but I would say 1/4 and 3/8 tempered respectively

Answer 2

At what distance ?
the farther the distance the less energy the round has. If shot through brush the round goes into a tumble and looses energy quickly
I haven't tried tempered steel but 1/4 to 3/8 mild steel will work under the right situation with good results