Originally posted by missileman
IMO booster motors do indeed have an ejection charge.
I get the impression that some of you guys have never read the insides of an Estes catalog. Then again, those catalogs are pretty much unavailable these days, and I can see where a newbie might have some confusion about what is what.
Estes-type BP motors are manufactured by starting with a cardboard tube and cutting a specified length to serve as the motor case. The nozzles are pressed/cooked into place, locking into the inside walls of the motor case. The main propellant BP load is pressed into place, and forms a single grain of BP that is also locked (by friction fit) to the inside walls of the case.
At this point, paths diverge.
Booster motors are complete at this point. No separate ejection charge is added.
Plugged motors get a solid, permanent plug added to the front of the propellant grain, then they are complete.
Single stage and upper stage motors continue to have components inserted in the case. Both have a measured amount of slow-burning (de-rated?) pyrotechnic material added to function as a delay charge; this material is pressed in place in front of the propellant grain and is locked in place inside the case wall. An ejection charge of coarse granular BP is lightly packed in the front next. Finally, a thin clay barrier is pressed into the front to retain the ejection charge and to discourage idiots from tampering with the motor contents.
The function of a booster motor, and especially the characteristics at burn-through, might be confused with normal single/upper stage motors with ejections charges. The gory details are a bit different, however. The booster motor is designed to release a charge of burning material (mixed gaseous, dusty, and chunky) at chamber combustion conditions (very hot, very high pressure, not necessarily high gaseous volume) in order to ignite the next motor. The single/upper stage motor is designed to burn an ejection charge to release a different mix (hot, dusty, hopefully not chunky) at moderate conditions (hot inside the motor but cooling rapidly, moderate pressure, very high gaseous volume) in order to activate the recovery system. These two motor operations are very different things. There are reasons why people tell you not to try to use single stage motors as boosters. There really is some rocket science inside here.