this is the can that I have problem with
DEAD LINK TO A GRAPHIC REMOVED
I guess you have resource of manual labor to assign and train to the packaging section and provide them simple tools and solutions.
My Suggestion:
Get some simple trays made which have 10 cavities that can hold 5 units each and this 5# can be easily and visually seen and counted. Let a counting person place 5 units in each of the 10 cavity of a tray and check same time the count and place 1 extra in the middle of the OK tray.
The packer person will pack all contents when he sees the centre unit in the tray and return empty tray back to the counting person. This way each pack will have atleast 50 or 51 units (your counting problem solved) and the trays can be reused over and over again.
See how it can work for you and how your people will appreciate the ease and method and adopt it with simple training.
By the way can you explain your counting of 50 units and the can packing process steps.