Egg shells are not grit. Same with oyster shell. It is a calcium supplement. It is soluble as in it gets ground up and digested.
Grit, whether store bought, rocks, pebbles, sand or dirt, is insoluble. It is used like sand paper to abrade what they eat into a fine mush they can digest and...
Wrong answer. Almost. But yes, If the grit is microscopic, it won't work on free range food. No grit is needed to commercial feed. But even fine sand/dirt will grind up nearly anything, even bone in a gizzard.
At 60+years of age, I never heard of any one ever buying grit for chickens...
Most brands include Silicon Dioxide (powdered Granite), not for grit, but as an "anti-caking" agent.
Just look on the ingredients in ANY bag or can of parmigian cheese. They used to use saw dust (cellulose fiber) exclusively as an a anti-caking agent but now better brands have switched to...
Buying ANY GRIT is a waste of money. It has never been needed. In days of old, chickens free ranged and got kitchen scraps and left over feed from other farm animals. They ate dirt, rocks or what ever they could find to grind it up in their gizzard.
Nowadays, commercial chicken feed (whether...