So I began my third time through the storyline on no future mode. (I was tired of my older character)
After I spawned the Mekiv Caverns and started the first Jumi quest; destroying everything like normal...Then after killing the first crab I saw...BAM! FullMetal dropped.

This item is a primary material without a type, (Similar to Coral or Shells) strange right? Well I did some tinkering before I got tired last night and took notes on the outcomes for weapons made with FullMetal.

I'm sure you'll like what you see as well.

Full Metal Essence Resistance:
(for those who use the tempering faq)
wisp-8,Shade-8,Dryad-8,Aura-8,Sala-8,Gnome-8,Jinn-8,Undine-8

Full Metal Weapon Base Attack-
Knife-55
Sword-57
Axe-57
2H Sword-71
2H Axe-72
Hammer-68
Spear-66
Staff-40
Glove-51
Flail-50
Bow-49 <(holy crap btw)

There you have it. Now if you pick up FullMetal, you don't have to spend all that restart time finding out what weapon to make with it.