I tried doing the sprue rubble thing many years ago (way before CoD), but it was VERY time intensive. Several hours work for a cupful (my dad DID have one of those manual cast-iron meat grinders, but it was used by him to make his own mince and sausages, and he'd have skinned me if I'd used it - back then, the electric ones were rare, and no-one threw out the metal ones.)
That said, If I had one today, then I'd use it, but it's harder to find them here than it would seem. It's a good idea, but it may not be worth the effort of hunting one down.
Hey! Where'd ... Everybody ... go?