A quick tip that can make your life easier when packing wheel bearings with grease is to use a grease needle on the end of your pneumatic grease gun. Simply fill between each of the rollers with grease.
Make sure you're using grease rated for wheel bearings. It has to be high temp and EP or extreme pressure but ask your supplier. Not all greases are compatible meaning they don't mix together so make sure you've cleaned all the old grease out first. Even after using the grease needle I still like to push a little bit more grease through by hand.
To be certain you've got enough grease in the bearing you need to see the grease coming out the other side the whole way around the bearing. Fill the hub so it's level from cone to cone. Do this all the way around the hub make sure there's no air pockets.