This information was provided by Tripoli Rocketry Association, Inc. Please visit their web site at: www.tripoli.org.
Black powder motors are manufactured by pressing black powder into paper casings using a powerful hydraulic press. The rear section of the motor then gets a clay nozzle, the forward end of the motor gets some chemicals to act as a delay and smoke generator. Following the delay chemicals is some loose black powder which forms the ejection charge. Holding the ejection charge into the paper casing is yet another layer of clay.
When the motor is launched the black powder burns at a controlled rate, providing thrust to the rocket. The propellant burns from the rear towards the front (end burning like a cigarette). Once the black powder has burned out the delay chemicals begin to burn for a pre-determined length of time. When the delay chemicals burn through to the ejection charge the ejection charge burns (quickly) -- launching the parachute out of the rocket.
The paper tube casing of the motor is good for only one firing. The insides of the paper tube are ablative and burn to protect the remainder of the paper tube. DO NOT TRY TO RELOAD these single use BP motors! Reloading these motors does NOT work... REALLY!
There are other forms of black powder motors, most notably are the large single use BP motors (once) manufactured by Rocket Flight. These big (G, H size) SU BP motors included titanium in the black powder. When the black powder burned the titanium is shot out of the motor, forming a large plume of sparks.
Some interesting BP motors:
E15 a discontinued Estes motor known for it's ability to cato (blow up, big
time)
C5 another Estes motor know for it's ability to burn a wee bit too rapidly
F100 a Flight Systems motor, great when they work (which is often or seldom
depending upon who you talk to)
H220SS now called the H330SS and currently not being manufactured. Has an
aluminum casing with an overwrap of paper. Shoots out sparks of burning
titanium.
B14 a discontinued Estes motor that was great for lifting heavy model
rockets. Rumor has it that the motor was converted (by hand) into a B14
by drilling out some of the propellant, forming a core-burning motor.