I've found the 3/8" axles are always filled with 10 ball bearings, but that leaves very little space to allow th bb's to move around. Sheldon Brown's rule for loose bb's is to fit them in until you can fit no more, then remove one.This will generally result in 9 bb's for the front axle. Read Sheldon Brown's page;
https://www.sheldonbrown.com/cone-adjustment.html
and
https://www.sheldonbrown.com/tooltips/hubs.html
and
https://www.sheldonbrown.com/harris/bearings.html
I can't find the statement regarding removing one ball; here is a discussion on bike forums.....
https://www.bikeforums.net/bicycle-m...each-side.html