I had 4 empty plastic trays from boxes of .45 ACP ammo I shot up. Three of them had flat sides on them and one didn't have sides. I glued them together with automotive type Amazing Goop. First I put down a piece of wax paper so I didn't glue it down to my desk. I held them together so tightly the sides caved in a little bit. The next day I flipped them over and filled the 2 cracks where the sides were bowed in with Goop, and let it flow over into the spaces between the walls and the part that actually holds the ammo. I shaved it flat with a knife the next day.
I don't reload and don't need a free loading block, but if I did, that's one way to get them. What I plan on using it for is unloading my pistol mags and being able to reload them without saving empty boxes, getting them out, using them, then putting the empty boxes away. If I want to take my mags apart and clean them this is where the ammo will be in the meantime. There are 60 holes and so 3 15 round mags (+ 1 round) will take up 3 out of 4 rows in each 3rd, (+1). That will sure make it easy to count how much ammo is in each mag. I can do the same thing with my 2 20 round mags, but not all of my mags at once. Each mag will fill a whole section. No more, and no less. So if I put 20 rounds in each black section, it will be easy to keep the ammo separated by a large physical space, and if I have 2 types of ammo, not mix them together.