I'm making a dragon in sandstone. The specifications say that the material escape hole must be 25mm or 4-10mm holes. I'll do that at the base of the dragon. My dragon is standing upright and I want to make the hole down the center of his neck as small as possible so that his neck will be as strong as possible. I'm making his head as thin as possible (2mm walls) to be light, so I know that there will be extra powder that must be shaken out. If I make the hole down the center of the neck between the head and the body about 4mm in diameter, will that be sufficient to empty the extra powder after it's built?