Making Rocket Nozzles
Rocket nozzles are a real topic of discussion amongst rocketeers. If you ask ten rocket-makers what they use to make nozzles, you will get at least eleven answers. So here is your first way to make nozzles. Keep asking and you will get the other answers.
I use clumping Kitty Litter as a base ingredient. I add 3% mineral oil, and about 10% graphite. I get the graphite at the farm store. They use it to lubricate corn planters. Press your rocket, and give it a try.
Most rocket people make their rockets right on the edge. When I started making rockets, I asked Tim Feider how to make good rockets. He said, "Get them to blow up consistently, then back off a little." That's what I did. However I did have some that failed, and I couldn't figure out why. At the PGI convention in Appleton, the rocket area was in a tent. I was pressing up some rockets, and there was a class being taught. Kurt Medlin, Steve Majdali, and John Steinberg were doing a class on one-pound black powder rockets. They were discussing nozzles, and I was listening in as I was working. One of them said, "Kitty Litter is supposed to absorb moisture. When it does, it swells." Well I thought that through. When my rockets blew up, it was always a few days later. Now the nozzle of a black powder rocket should be half of the inside diameter of the tube. So a one-pound rocket is 3/4 of an inch, so half of that should be 3/8 of an inch. I took a rocket that I made a few days earlier, and by hand I turned a 3/8 drill through the nozzle, and a bit of clay was removed. It had swollen up a bit in the humid August air. So my suggestion is to always check the nozzle inside diameter the day that you fly the rocket. I have never had a rocket, filled with a tested fuel, blow when I have done this.