If I want to grind for a fragnum, or a striker what should I put in the grinder? Is it yellow for yellow? If I want a yellow rarity do I need to put all yellow’s in? Also the machine never seems to give me the option of doing a moonstone grind even when I have all the same rarity gun in the machine, is there a secret to getting the option of moonstone grind?
There’s a thread for that:
The *specific" item you get is still subject to RNG, but you can at least be more deliberate about getting the rarity you want.
Don’t bother trying to grind three purples into a legendary though - the odds without moonstones are way too low, and you can only moonstone grind three purples if they are class mods.
There are other restrictions on moonstone grinding as well, but that’s the main one I can think of which could be causing issues for you.