I would buy a hand roller the type thats fillable with water,just load the shells in it and some round stones that will fit in and roll away. If you have a lawn tractor take it for a tow.Its my version of stone ground. I also do something similar on a smaller scale with eggshells. Got a 3 pound plastic coffee container and 4 stones golfball size and smaller,i dry the shells for a day or two in the sun,toss them in and shake away. After about ten minutes you have a mix of dust and small pieces,which you can mix in the feed or its a great shot of calcium for the garden. Tomatoes,cukes,squash,eggplants and all peppers are calcim loving plants.
