Must have been good fun shovelling the shot out, up to your backside in water. Or maybe they drained the water (pollution?) and had a swag of buckets in there.

There must have been a screening process as well, to ensure that the shot were the same size as each other.

When I was a freshwater angler in England, the split-shot we used for weights were carefully organised so that each shot was twice the weight of the last one. I can't remember them all, but they started at dust-shot, and there was No.4, No.8, BB, AA, and swan-shot. I seem to remember that BB shot was .177calibre, AA was .22calibre.