Machine gun ammo recipe in Requiem

No story spoilers here, but I’m trying to complete the Master Craftsman challenge, and I have never unlocked the final crafting recipe in either of my playthroughs. I looked it up, and it turns out the one I’m missing is machine gun ammo? Tried looking up where to find the machine gun ammo recipe and all I’m finding is how to get the Requiem ammo recipe. Someone please help me lol