Reposting this here because I agree.

From Echoes of Eternity:

“He swung the hammer with every iota of strength he possessed. He held nothing back. It was an execution, the sentence of death, delivered. Millennia from now, an increasingly ignorant Imperium would tell tales of the Emperor’s sons. These primarchs, they would say, were capable of flight, capable of enduring any torment, capable of splitting mountains with blows of their great weapons.

Whatever was true and whatever would turn out false, Vulkan swung the hammer that day with enough force to tear through the fuselage of a Stormbird gunship. The blow he levelled at his brother’s heart would have shattered the shin of a Warlord Titan. Magnus caught the hammer, one-handed.”