So those of you who have flown model rockets remember the motors used for that. They are about 3/4 inch in diameter and something like 2+1/2 inches long. You could get them in four basic ranges when I was a teenager: A, B, C and D. Each letter is twice as powerful as the previous letter, so a C is four times as powerful as an A and so on. With a really powerful motor and a rocket weighing a few ounces, you could see flights of about 1500 feet.
But now I have grown up and I like stronger stuff.
This is a J motor. It's over 2 inches in diameter and about 13 inches long. Rather than compressed black powder, these use a composite propellant that is about 3 times as powerful per volume. Since the doubling per successive letter continues, we can see that this is 512 times as powerful as an A motor. There's about a pound of propellant in that aluminum case, and it took my 11-pound rocket to a reported altitude of 4905 feet today.
Today's launch was doubly cool because I got exactly the same reported altitude last month on a commercially-produced motor of the same size; this one is one my uncle and I made for about 1/3 the cost.
Here's my rocket just before I elevated the launch rail:
And here it is as recovered:
Another great thing about the day was that there was a Scout troop from Santa Barbara camping nearby and launching model rockets. They came by to say hi, and we did a little show and tell for them with some of our rockets and motors and avionics and such. They had also found a rocket out in the desert, and it turned out to be one my uncle had lost in September. We came home with more rockets that we went with, which is kind of unusual for us.