What principle of operation does the M9 service pistol use to thrust the barrel group rearward?

The M9 service pistol operates on the recoil-operated principle. This principle means that when the pistol is fired, the energy from the fired cartridge causes the barrel and slide to move rearward. The design utilizes the force generated by the expanding gases from the fired round to cycle the action. The recoil movement assists in ejecting the spent cartridge, allowing the next round to be fed into the chamber.

In contrast, the blowback principle relies solely on the inertia of the slide and the pressure of the propellant gases, which is more commonly found in simpler firearm designs, particularly those that handle lower-powered cartridges.

The gas-operated mechanism, on the other hand, uses a portion of the gas produced from firing to cycle the action, as seen in rifles like the M16. Lastly, the cylinder principle usually refers to revolvers, where chambers rotate around a central axis to align with the barrel. Thus, understanding the specific mechanics of the M9 emphasizes how efficiently it handles the recoil of each shot fired to keep the firing cycle operating smoothly.