An integrally suppressed handgun comprising: a longitudinal axis; a frame; a receiver attached to the frame; an elongated barrel insert comprising a rearward mounting portion fixedly coupled to the receiver and a forward retention portion, the barrel insert comprising a rear breech end defining a chamber configured for holding an ammunition cartridge, a front end, and a longitudinally-extending barrel bore defining a projectile pathway; the barrel insert further comprising a plurality of radial gas ports in fluid communication with the barrel bore; a suppressor mounting adapter at least partially surrounding and removably coupled to the barrel insert, the mounting adapter comprising an upper through passage receiving the barrel insert at least partially therein and a lower through passage; an annular gas expansion chamber formed between the barrel insert and the mounting adapter in the upper through passage; a threaded muzzle cap removably coupling the mounting adapter to the barrel insert; a baffle assembly (240, 300, 301) removably coupled to the mounting adapter and defining a front end of the handgun including a projectile exit aperture, the baffle assembly comprising a plurality of sound suppression baffles arranged in longitudinally stacked relationship, each baffle defining an internal baffle gas expansion chamber; and an elongated mounting rod extending from the front end of the baffle assembly rearward to the mounting adapter, a threaded rear end of the mounting rod threadably coupled to the mounting adapter to retain the baffle assembly; wherein when the handgun is discharged, the annular gas expansion chamber fills with combustion gas vented from the gas ports of the barrel insert. a longitudinal axis; a frame; a receiver attached to the frame; an elongated barrel insert comprising a rearward mounting portion fixedly coupled to the receiver and a forward retention portion, the barrel insert comprising a rear breech end defining a chamber configured for holding an ammunition cartridge, a front end, and a longitudinally-extending barrel bore defining a projectile pathway; the barrel insert further comprising a plurality of radial gas ports in fluid communication with the barrel bore; a suppressor mounting adapter at least partially surrounding and removably coupled to the barrel insert, the mounting adapter comprising an upper through passage receiving the barrel insert at least partially therein and a lower through passage; an annular gas expansion chamber formed between the barrel insert and the mounting adapter in the upper through passage; a threaded muzzle cap removably coupling the mounting adapter to the barrel insert; a baffle assembly (240, 300, 301) removably coupled to the mounting adapter and defining a front end of the handgun including a projectile exit aperture, the baffle assembly comprising a plurality of sound suppression baffles arranged in longitudinally stacked relationship, each baffle defining an internal baffle gas expansion chamber; and an elongated mounting rod extending from the front end of the baffle assembly rearward to the mounting adapter, a threaded rear end of the mounting rod threadably coupled to the mounting adapter to retain the baffle assembly; wherein when the handgun is discharged, the annular gas expansion chamber fills with combustion gas vented from the gas ports of the barrel insert.