If you are a person like me and have trouble getting chemicals to make powder, then it's hard to do much. One option is Estes powder. The main downside of this is high cost (a six pack of C's is $10) and it is quite time consuming. Always get C size engines, A's and B's have a lot less powder and cost almost as much. D size is too expensive and quite a bit harder to powder. They are for model rockets, but use a black powder solid propellant. If it is an option, bottle rocket powder is preferable because it is easier and cheaper (as long as you get a good price).

Safety: Always wear heavy cotton or leather gloves and safety goggles. A dust mask is also good. Have you ever had "powder nose"? It's when you get powder that's floating in the air in you nose. Not only do you sneeze and stuff, you get black snot.

There are many methods of doing this, and probably better ones, but this is how I do it.

Update: An alternate, and most likely faster way is this: Once the core is removed (following instructions below) wrap it in a plastic bag, place it on a hard surface, and just smash it with a hammer. I havenÔø‡t tried this because I donÔø‡t bother crushing engines anymore, so while IÔø‡m sure it works fine, the bag will get holes in it. Wrapping the whole thing in a few layers of kraft paper or something may help deal with this problem.

Equipment:

Film containers or similar small, soft plastic containers
Larger strong container
Smashing tool (I use a 12" long nail, your tool should be close to the diameter of the small container, with a little space)

Procedure:

1) Peel off the cardboard from the engine (just make a cut with a knife and peel).
2) Break off clay nozzle (you can just break it off with your hands).
3) Scrape off clay on ejection charge (save ejections charge grains, but you don't need to spend all day picking grains of powder out of a pile of clay. Just do a quick job).
4) Put engine core in large container and pound it. When its in about 5 or more pieces about equal size (this doesn't need to be all scientific and exact) you can stop.
5) Put some of these smaller piece in the film container and pound it. Once its in pretty small pieces, pound another bigger chunk.
6) Repeat step 5 until there are no big chucks.
7) Now you will have powder with small chunks in it. Remove the chunks and crush them some more. To separate powder from chunks, you can just put it all in you larger container and tap in a bunch on the table or something. In case you haven't realized it yet, this makes the chunks come up to the top and you can shake them out and pound them more. Do this until it is all very fine powder. After a while, you'll figure it out and it will go a lot faster.
8) Store in a sturdy plastic container until use.

Estes engines

Unrolling

All unrolled

The inside of an engine

Safety gear

My crushing nail

Partially crushed

Final powder