I'm not sure what kind of calcium the rest of you are using, but the oyster shell I buy in a 50# bag will clog up in an opening that small. I'm going to try to make a dispenser out of either a large diameter pipe or plywood like my feed dispenser.
I'm just wondering how well that actually dispenses the oyster shell? The stuff I've used in the past seems like it might be prone to clogging up at the neck of the wine bottle. I like the idea though.