You only have to worry about the powder bridging and getting a squib load. It can't double charge because the cavity is set for a certain amount and won't let more than that in. As long as you are using the disks that came with it you should be OK. The adjustable charge bar and Unique don't get along with smaller loads. The light so you can see the charge before you set the bullet on is a great idea. I have done the same thing since the time I had to pull 93 bullets.
Rusty