The remaining BBs are then either put through caliber-specific gauges to make sure they are the correct size, or they are individually dropped down the shot tube of the rifle they are going to be used in.
As Lee Nelson, a BB gun coach with the Gallatin Valley Sharpshooters in Montana, explained, the drop technique operates on the Goldilocks principal. "I cover the lower end of the tube with my finger and drop the BB down," he said. "The ones that fall too fast or too slow get put aside. The BBs that fall at a nice, steady rate are the keepers."
It's a tedious process, but it's necessary.