How are crime bullets and cartridge cases matched with firearms?

Forensic ballistics — the firearms-and-ammunition science: the interior (the firing's physics), the exterior (the projectile's flight), the terminal (the impact's effects) — and the forensic's own: the comparison (the fired evidence's matching). The classification (the exam's core): 1. By the bore: the smooth-bore (the shotguns — the pellets' spread) vs the rifled (the pistols, revolvers, rifles — the spin's accuracy). 2. By the size-and-hand: the handguns (the pistols-semiautomatic; the revolvers-cylinder) vs the shoulder (the rifles; the shotguns; the carbines). 3. By the action: the manual (the bolt, lever, break) vs the self-loading (the semi; the full-auto — the machine guns). 4. By the calibre (the bore's diameter — the mm-and-gauge's measures).