Rigby,
I use a nitrocard over the charge and then fiber wads to take up the airspace for my bluedot loads.It would be possible, with the cases I am using, for the bullet to fall or be pushed back into the case, if there was an air space. 12 to 1 was the recommended Holland spec for casting in their bore rifles but you could go harder. I wouldn't shoot multiples, why would you want to, this is a rifle not a shotgun? You need to get the appropriate round ball mold or bullets for your gun just to see how they print on the target. What is your bore and groove diameter?