[DeepSouthBamaGRITS]

I, too, have a meat grinder that grinds bones (got it when I was raw feeding my Yorkie). But what I do when grinding the roasted bones for bone meal is put them in some sort of plastic bag (Ziploc baggie, bread bag or double/triple some plastic grocery bags). I have a meat tenderizer (heavy duty) that I use to smash the bones (cover plastic bag with a doubled towel) and pound away. Those that don’t smash up, I will sift contents of the bag to get out what did crush, then take outside and crush bigger/harder bones (like a ham bone, leg bones, etc.) with a small sledge hammer. That usually does the job, then I will sift that and any remaining bones, I will try crushing again with the sledge. I usually try to really roast/almost burn the bones before I crush. Some of the smaller bones will crush with your fingers, larger bones don’t. I will sometimes roast those even more before trying to crush, depending on how many or how large they are (like deer leg bones, ham bones, etc.). Or I will save those bones in a baggie to re-roast when I have another batch to do.
Another thing I have done is put them in a fire outside. If I’m burning or have a campfire, etc., I will put the bones on an old cookie sheet and sit on top of the fire. This really works good because the heat is really intense & will roast the bones a lot quicker, even those big bones. But I don’t always have a fire going when I have bones to roast. Just giving you some other options.
I don’t like using my grinder to grind bones (even tho it is designed to do so) as it really dulls the blades. and can even chip them.