text: Geometric APCP deflagrates from the surface of exposed propellant in the combustion chamber. In this fashion, the geometry of the propellant inside the rocket motor plays an important role in the overall motor performance. As the surface of the propellant burns, the shape evolves (a subject of study in internal ballistics), most often changing the propellant surface area exposed to the combustion gases. The mass flux (kg/s) [and therefore pressure] of combustion gases generated is a function of the instantaneous surface area  (m2), propellant density  (kg/m3), and linear burn rate  (m/s):
  Several geometric configurations are often used depending on the application and desired thrust curve:
  Circular bore: if in BATES configuration, produces progressive-regressive thrust curve.
  End burner: propellant burns from one axial end to another producing steady long burn, though has thermal difficulties, CG shift.
  C-slot: propellant with large wedge cut out of the side (along axial direction), producing fairly long regressive thrust, though has thermal difficulties and asymmetric CG characteristics.
  Moon burner: off-center circular bore produces progressive-regressive long burn though has slight asymmetric CG characteristics.
  Finocyl: usually a 5 or 6 legged star-like shape that can produce very level thrust, with a bit quicker burn than circular bore due to increased surface area.
  Burn rate
  While the surface area can be easily tailored by careful geometric design of the propellant, the burn rate is dependent on several subtle factors:
  Propellant chemical composition.
  AP, Al, additive particle sizes.
  Combustion pressure.
  Heat transfer characteristics.
  Erosive burning (high-velocity flow moving past the propellant).