I Crush them into fine pieces and mix with feed. No bake or microwave, Just rinse and crush. Much better than Oyster shell. The feed has calcium in it. They free range half the day, After I get home from work.
I have been grinding the shells up in a coffee grinder for about four months now. I just rinse them up in water. I have not had a problem so far. I sprinkle the shells in the feed a little at a time.