Internal Ballistics
Everything that happens from primer ignition until the bullet exits the muzzle, governed by pressure, powder burn rate, and barrel behavior.
Internal ballistics covers the brief, violent window from the moment the primer lights the powder to the instant the bullet clears the muzzle. During that span the powder generates expanding gas that drives chamber pressure up steeply, and the burn rate of the propellant determines how fast that pressure peaks and how it tapers as the bullet accelerates down the bore.
Understanding this phase is the heart of safe, accurate handloading. The same firing event sets the barrel vibrating, and consistent barrel harmonics help every shot leave the muzzle at the same point in that vibration cycle. Even the lock time before ignition plays a small role, because a steadier rifle at the moment of firing produces a more uniform result.