Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin, and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and sulfuric acid. One of its first major uses was as guncotton, a replacement for gunpowder as a propellant in firearms.
Guncotton was actually developed as a “Smokeless Gun Powder”,
Essentially, the main difference between Black Gun Powder and Smokeless Gun Powder is that you need almost zero incombustible components. The key problem with black powder was that it produced a cloud of smoke, not only from Un combusted carbon but also, unavoidably, from ash, the salts formed from whatever anion happened to latch on to the sodium or potassium cations present from the nitrates in black powders. Black powder ash contains a high proportion of potassium or sodium sulfates and carbonates, and because the inorganic saltpeter component was about 2/3 of the total weight of black powder, you had a lot of ash.
Modern smokeless powder has also had a couple of properties that make it useful over long periods:
It must be relatively inert: you don't want a substance like pure nitroglycerine that is shock sensitive. That property is for the primer (more on that below) and is a very bad idea for the propellant itself.
It must remain relatively inert: early smokeless gunpowder had volatile components like camphor that would evaporate after a few years, leaving a considerably less stable substance. Others had volatile components that would decompose over time and result in spontaneous explosions.
At some point during the production process, it must be Plastic: you need to be able to form the propellant into a useful shape to put it into a cartridge. It means that it needs to be able to fit a mold. Actual powders will do.
It must be explosive, but not too explosive: too high of a gas velocity and you get a high explosive, where the flame front exceeds the speed of sound and the stress on your gun barrel is very high. No one wants their gun to blow up in their faces.