You shooting a .20 ga.? If so, get you a 5/8" dowel and some post it notes. Wrap the post it around the dowel and stick it to itself. Then fold one end over the end of the dowel like you would a coin wrapper. Then measure the amount of shot you want to use into it. You can then take it off the dowel, unfold it, and measure the length. Then you can cut all the post its to the length while they are still on the pad. Then each one will be the right length for that shot charge. Make them up, start one in barrel, pour in shot, add overshot card, and ram it all down at once. It helps if you drill a small hole through your overpowder wad to let the air escape. I drill a 1/16" hole.