What is "brown powder"

Brown powder or prismatic powder, sometimes referred as "cocoa powder" due to its color, was an explosive-based propellant used in large artillery and ship's guns from about the 1870s. While similar to black powder, it had slower, gentler, burning rates; and used less-reactive fuel ingredients. Further modifications of its burning rate were achieved by shaping the powder grains into prismatic shapes, typically single-perforated hexagonal or octagonal prisms. They became obsolete as a propellant due to the introduction of nitro-explosive propellants such as Poudre B, in France, and later by cordite, in Britain. These new propellants produced less smoke, particularly less black smoke.