The Alloy of Law (Mistborn #4)

Centuries after the Mistborn trilogy, Scadrial is on the verge of modernity - railroads, electric street lights, and skyscrapers. Waxillium Ladrian can Push on metals with his Allomancy and use Feruchemy to become lighter or heavier at will. After 20 years in the dusty Roughs, in the city of Elendel, the new head of a noble house may need to keep his guns.