The Capsule ammo's mouse over text-box states that both the Engineer or Assembling Machines can construct ammo. But only Assembling Machines can. I’m not sure if the Engineer is meant to be able to as well, or if the text-box info is incorrect.

Fun mod though! I have mods to make the biters more dangerous and the capsule launchers really help my defences from crumbling. :)

This is a deliberate choice. I made this item non craftable by hand as it would take a lot of space in the crafting menu for an item that doesn't really ever need to be crafted by hand. I don't know why the text box is saying it should be craftable though. I will add it to the list of issues for next time I can work on the mod, but don't expect this to be fixed anytime soon as I am really busy these days.

I'm glad you are enjoying my mod !