Metallurgic Summonings

Oracle Text

Whenever you cast an instant or sorcery spell, create an X/X colorless Construct artifact creature token, where X is that spell's converted mana cost.

3UU, Exile Metallurgic Summonings: Return all instant and sorcery cards from your graveyard to your hand. Activate this ability only if you control six or more artifacts.

Card Rulings

9/20/2016 For a spell with in its mana cost, use the value chosen for X to determine its converted mana cost. For example, Clash of Wills is an instant spell with mana cost . If you chose 2 as the value of X, then Clash of Wills has converted mana cost 3, and Metallurgic Summonings’s ability will create a 3/3 token.
9/20/2016 Metallurgic Summonings’s first ability resolves before the spell that caused it to trigger.
9/20/2016 If Metallurgic Summonings’s first ability resolves and the spell that caused it to trigger has been countered, use that spell’s converted mana cost as it last existed on the stack to determine the value of X.
9/20/2016 The number of artifacts you control is checked only as you activate Metallurgic Summonings’s last ability. It’s not checked again as it resolves.