text: The composition of APCP can vary significantly depending on the application, intended burn characteristics, and constraints such as nozzle thermal limitations or specific impulse (Isp). Rough mass proportions (in high-performance configurations) tend to be about 70/15/15 AP/HTPB/Al, though fairly high performance "low-smoke" can have compositions of roughly 80/18/2 AP/HTPB/Al. While metal fuel is not required in APCP, most formulations include at least a few percent as a combustion stabilizer, propellant opacifier (to limit excessive infrared propellant preheating), and increase the temperature of the combustion gases (increasing Isp).
  Common components
  Oxidizers
  Ammonium perchlorate as the primary oxidizer
  Metal-oxide catalysts as thermite oxidizers
  High energy fuels
  Aluminium (high performance, most common)
  Magnesium (medium performance)
  Zinc (low performance)
  Low energy fuels acting as binders
  Hydroxyl-terminated polybutadiene (HTPB)
  Carboxyl-terminated polybutadiene (CTPB)
  Polybutadiene acrylonitrile (PBAN)
  Special considerations
  Though increasing the ratio of metal-fuel to oxidizer up to the stoichiometric point increases the combustion temperature, the presence of an increasing molar fraction of metal oxides, particularly aluminium oxide (Al2O3) precipitating from the gaseous solution creates globules of solids or liquids that slow down the flow velocity as the mean molecular mass of the flow increases. In addition, the chemical composition of the gases changes, varying the effective heat capacity of the gas. Because of these phenomena, there exists an optimal non-stoichiometric composition for maximizing Isp of roughly 16% by mass, assuming the combustion reaction goes to completion inside the combustion chamber.