You may want to check my simplified version, no BBs needed:
https://makerworld.com/en/models/499996#profileId-414910

This is another version of my external spool holder for the A1/A1 mini with rollers made using Airsoft BBs.
Just print 2 parts (there are 3 because one is pre-supported), insert the BBs and screw it back to the original hole.

You'll need about 30 BBs, 15 to be inserted into each end.