u/BeneficialDatabase69

So I’m not understanding how to raise expertise levels. I tried to raise my turmoil (named knee pads) level and I was only able to upgrade it to lvl 4. I see that I’m exp 4 and I can’t go higher than that.

It gave me an option to donate junk but when I pressed the button nothing happened.

Do I have to have multiple turmoil copies to donate it as junk to raise that items level?

Say I need to upgrade a gr9, can I only donate gr9 junk or can it be any lmg?

Say I need to upgrade foundary bulwark chestplate , can I only donate foundary bulwark chest plates or can it be any foundary bulwark piece?