As mentioned by Musicspren I'm also curious about Miles . . .
What combos could be so potent as to be able to dismiss being shot in the head?
We know that pewter makes you tougher, maybe pewter/pewter would give you bullet resistant skin? I don't think it'd be gold/gold for super health. If you got shot in the head and killed before you could burn the metalmind it wouldn't be of much use. Even if you were burning the gold, would you still be able to keep burning with a bullet in the brain?
I think that it'd either be pewter/pewter for bullet resistant flesh, or maybe a pewter/steel for super speed and dexterity.
Pewter/gold maybe? A pewterarm with gold healing might be able to survive a gunshot to the head.