This section discusses weapon design practice as it directly applies to interior ballistics. The design of gun systems is so complex that it is best dealt with as a chapter in its own right. We begin with an introduction to fatigue so that some understanding of the basic principles in gun design can be developed. We then proceed to discuss some introductory concepts in tube design, gun dynamics, and muzzle devices. The reader is directed to the references for a more in-depth treatment of these topics.