Discussion:

Just nosey curiosity, but also serious inquiry; why is single base powder less flashy? LB

Double based powders have an inner "core" of one type of propellant, and a coating of a different type. The outer layer burns slower than the inner, causing a slower buildup of pressure at the start of bullet movement, then the inner core burns much faster, giving a "boost" to the projectile. In shorter barrels, some of the inner core exits the muzzle before it is completely burned, resulting in muzzle flash due to the unburned powder. At least, this is the way it was explained to me. Hope that this helps.