You do not have the testgamemode set to your mod in the world settings for your level. That’s why they do not show up.
Also, you don’t need to specify a map under the PrimalGameData_BP entry anymore either. In fact if you have TheIsland specified, my understanding is that it won’t work on other maps.
BTW, if you want to make them craftable in the fabricator, do this: (first untick “Give blueprint to player inventory” on each of your engram entries)
Then modify PrimalGameData_BP_Chaingun as such: Find “Additional structure engrams” and click the + once. Set it to “Storagebox_fabricator” in the section labeled “for class”. Click the + next to “Class additions” twice. Set those to your 2 items. IE: PrimalItem_WeaponChaingun & PrimalItemAmmo_ChaingunAmmo.
Once you have that set, open up PrimalItem_WeaponChaingun & PrimalItemAmmo_ChaingunAmmo and look for “Crafting requires inventory component”. Click the plus 1 time. Select PrimalInventoryBP_Fabricator. Do that for the ammo and gun bp.
Save, cook, upload and start chain-gunning!
P.S. You will have to create a new fabricator for them to be craftable. They will not show up as BP’s in a pre-existing fabricator, only in ones made after adding the mod.