Simon, thanks for your help. Your posts have been particularly useful.

I was not aware of these motors, but they change things a bit. I did not realize that the KNSU motors needed to be heavier. It looks like Aerotech G-12's are available in 2-packs for just $21 - not bad (although I'd have to pay that annoying HAZMAT charge.)

Perhaps I will use commercial motors. They are pretty cheap, have no ejection charge, and clearly have superior characteristics compared to the KNSU rockets.

I'll look into these more. Thanks for your help!