This tray is to hold the single shot BBs for 4H competition shooting. Use 8mm x 2mm magnet discs. Nothing complex or anything use CA (superglue) to hold the magnets in place. A very small drop of CA. I used a drop about the size of a pin head.

Magnets:
https://www.amazon.com/gp/product/B07D9RXPHP/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

I painted the tray rim with black Sharpie. You can print with 2 colors.

Creality

Ender 3 Pro

No

No

whatever - i used .16

20% - whatever you choose