Pretty sure they just fill the pots. Most pots are a standard size (100/140/160 etc) so if they buy 100 shot pods, they'll all hold roughly 100 so no real need to count or measure.
the best one that sites used were made by powerball and the only link i can find shows it in an image here: http://www.powerball.co.uk/accessories_products.html
however i don't think they are even made any more but they were awesome, automatically counts out 100 and puts it in the pod at the pull of a lever.