When the first smokeless propellant for guns (nitrocellulose) was developed, it could not be used in large bore guns because it burned TOO FAST, destroying the gun. It was discovered that adding one particular additive to nitrocellulose gunpowder drastically SLOWED combustion, make the gunpowder+additive safe for guns. In addition, the additive actually increased the energy in the powder, improving performance. What was this amazing additive, that slowed combustion while increasing energy? NITROGLYCERINE! [Google "double base gunpowder" for further information.]