Black powder rocket propellant is a lot like old fashioned gunpowder. It has one different part called a binder. The binder is usually a substance called Dextrin. One common model rocket engine company is Estes Industries. Their motors are made with black powder propellant. Black powder propellant must be pressed very tightly to work well. If it is not packed tightly, it will burn too fast and might explode. A simple way of combining the parts to make black powder rocket propellant is: 75% potassium nitrate, 10% sulphur, and 15% charcoal. This is the most common way of making it. Dextrin may be added as a binder (usually between 0 and 5%). Extra (coarse) charcoal or metal powders (5 - 10%) may be added to make a spark trail. Adding these extras might change how fast the fuel burns.