ROCK ISLAND ARSENAL, Ill. — In the forge at Rock Island Arsenal, workers in silver heat suits and darkened face shields shovel fire unfazed as flames lick their feet and legs. Their work is older than the nation’s railroads, melting and molding metal the way it’s been done for centuries. Sparks cascade as they raise a cauldron of molten metal from the flames along the ceiling to a set of empty molds. They pour the orange liquid into molds, judging the flow by sight and instinct. The scene feels