Image from Sugar Shot to Space.
Experimental rocketry, EX for short, has been around longer than hobby rocketry. Experimental rockets were among the first modern rockets to be built, including the first bi-propellant rocket built and flown by Robert Goddard about 86 years ago. One must be very careful to learn before building, as rocket propellants are flammible, and rocket motors frequently explode when they fail. In addition, it is essential to obey all laws and safety recommendations from the experts. But many Americans, and people all over the world, build their own rocket motors rather than buy them from a vendor. These people build their own motors and discuss motor building, internationally. They do so legally. Information about rocketry and propellants is public domain knowledge. Discussion of this information is protected by the bill of rights. Public libraries, websites, universities, they all contain information about rockets and how to build them. Obviously one should survey the field, and consider purchasing a book on the topic, long before actually building a rocket motor. One should talk to, and work with other EX builders. Many NAR/Tripoli launches have EX flights, or have flyers who are part-time in EX. Talking to them will be your most valuable source of information. Here is some preliminary reading: