A delayed rotary blowback mechanism integrated into a firearm bolt and carrier subassembly. A plurality of lugs are configured at a rear of the bolt and seat within a mating profile of a barrel extension of the firearm in a fully chambered position. Chamfered locations are configured between the lugs and a receiving profile in the barrel extension for influencing linear to rotational motion of the bolt. A cam pin extends upwardly from the bolt and seats through a circumferentially directed slot configured within the bolt carrier. Upon initiating of the discharge cycle of a fired round traveling out the end of the barrel, the chamfered configuration results in the bolt and cam pin rotating within the carrier and the lugs subsequently separating from the barrel extension. The bolt and carrier retain sufficient inertia to cycle through the discharge cycle concurrent with reloading a subsequent cartridge.