This discipline involves the action and interaction of each and every part, both moving and stationary, within the firearm. Most hobbyists are limited to a familiarity with the difference between a bolt action and a lever action. However, in reality, this is far more involved. It also includes the manufacturing tolerances of each part and how that affects the function. Since this is post-manufacture activity, this also involves how a particular firearm functioned, or failed to function, in any given incident.