You can target 1 "Red-Eyes" monster you control, except "Red-Eyes B. Chick"; equip this monster from your hand or your side of the field to that target. It gains 600 ATK. If this card is sent from the field to the Graveyard: You can add 1 "Red-Eyes" card from your Deck to your hand, except "Red-Eyes B. Chick".
Equipping itself to another monster is slow and a waste of resources.
Black Metal Dragon’s best effect is its ability to search, so you might want to use it even if it’s just for that.
Black Metal Dragon can search out Red-Eyes monsters and Red-Eyes Spell/Trap cards, so keeping that in mind here are some of the best targets. When searching for a Red-Eyes Spell/Trap it is better to search Red-Eyes Insight, then use that Red-Eyes Insight to search out the intended Spell/Trap.