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Locking is a term used on breech loading firearms referring to when the bolt engages with some type of mechanism that binds it to the chamber.

Locking is found on most breech loading firearm operations that are chambered to fire high pressure rounds, in particular rifle cartridges. They are found not only on manually operated firearms (IE:Lever action/Bolt action) but also automatic firearms such as, Gas operated, Recoil operated.

Locking components on firearms that use higher pressure rounds (IE: Rifles) are found on barrel trunnions/bolts and machined receivers on most firearms. On most General Purpose Machine Guns which use QC barrels, it must be noted that locking lugs are used on the barrel nut rather than the trunnion.

Although similar, it must be noted that Delayed blowback firearm operations do not use locking but use similar operations to delay the opening.

Examples

Rotating bolt

Rotating bolt is where the bolt, regardless of the weapons operation rotates to lock/unlock from the receiver/barrel/trunnion. Gas operated examples using this operation are the AR-15. Recoil operated examples using this operation are the Barrett M82.

Roller locking

Roller locking is where the bolt, regardless of the weapons operation uses rollers that lock/unlock itself into the trunnion/receiver. Gas operated examples using this operation are the T28 rifle. Recoil operated examples using this operation are the Rheinmetall MG3.

Flapper locking

Flapper locking is where the bolt, regardless of the weapons operation uses flappers that lock/unlock itself into the trunnion/receiver. It must be noted that this form is similar to the mentioned roller locking. Gas operated examples using this operation are the EM-2.

Toggle locking

Toggle locking is where the bolt, regardless of the weapons operation uses a toggle that lock/unlock the bolt. Gas operated examples are the Japanese Pedersen rifle. Recoil operated examples are the Vickers machine gun.

Tilting bolt

Tilting bolt is where the bolt, regardless of the weapons operation tilts to lock/unlock itself from the receiver. Gas operated examples using this operation are the FN FAL.

Wedge locking

Wedge locking is where the bolt, regardless of the weapons operation tilts to lock/unlock itself from the receiver. Gas operated examples using this operation are the Browning Automatic Rifle. Recoil operated examples using this operation are the M2 Browning.

Collet locking

Collet locking is where the bolt prongs operate as locking lugs that lock/unlock by wedging into the receiver/trunnion. Collet locking examples are the Blaser R93.