I used to glue the fins right onto the motor.
Made some rocket cars as well.
Never though to cut one open though...
:)
Removing the cardboard casing and taping the igniter to the side of the propellant block gets you a four-foot ball of brilliant magenta flame that lasts 2-3 seconds and generates a pungent cloud of sulfurous smoke.
FABULOUS for disrupting a sophomore high school biology class.
Placement back among the lab tables away from student desks is crucial, and timing is essential to achieving the maximum number of observers at the maximum safe observing distance.