I just picked up 2 differnt items one is #2 poultry grit, and the other is oyster shells and my question is are they the same thing. i know the oyster shells are used for calcium but are they also used for grit? i just bought the two to be safe and was going to mix them together. and also i save my egg shells and feed them back as well. just wondering, ive never feed them grit or anything because there free ranging all the time and i have a sand pit and gravel driveway, but with winter around the corner i though i better start to have it by there food to be safe.