Locked-breech

Locked breech is a firearms term used to describe the design of a breech reloading firearm's action. The term is important in understanding how a self reloading firearm works. In the simplest terms, it's one way to slow down the opening of the breech of a self-reloading firearm when fired. The source of power for the movement is recoil (see below)

The simple principle of firing a projectile is that when the propellant in the chamber (the gunpowder in the casing) is ignited and burns quickly for a very short time. This creates pressure that pushes the projectile (bullet) out of the chamber and down the barrel of the firearm. The pressures involved in this are very high for a very short time. If the high pressure gas was not confined for some time it would inflict major damage. Especially to parts of the firearm that are not capable of withstanding those pressures, this is also dangerous for the person firing the firearm. The feature of a 'locked breech' barrel is that it confines the high pressure gas. The propellant burns for a very short time, so propulsion continues for a very short time while the gases expand and cool in the barrel. Because of the pressure drop breech block can be opened in a self reloading firearm due to the recoil inertia generation by the movement of the projectile.

The main difference is that there is a very strong lock in the locked breech action where the blowback systems rely more on springs and the weight of components to provide safe operation. The type of action used by a firearms designer will be determined by the design goal inherent for that firearm. The three actions describe are increasing more expensive to manufacture.

Recoil is described by Newton's Third Law of Motion, which states that for every action there is an equal and opposite reaction. This force is felt in the hand or on the shoulder when a person fires a handgun or a rifle. It takes the form of a quick sharp push away from the path the bullet is flying in and directly against the hand or shoulder of the shooter.

The locked breech systems in handguns and rifle vary a great deal. The photograph showing four handgun barrels illustrates the evolution of handgun locked breech systems in four of the most famous firearms. This is from the Browning Hi-Power (I in the photograph), John Browning's last design. The second barrel is of the same action type in the CZ model 75 handgun. The third barrel type is from an HK USP pistol. The fourth barrel is from a Glock (which uses the Sig Sauer system).

The photograph on the right is of a different type of locking system. This one is the Beretta Rotary locking system found in their PX Four Storm handgun. The next photograph on the left is of the CZ model 52 showing a roller locking system. Some sources describe this as a delayed blowback action but it is actually a locked breech.

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