Selectable dual mode trigger for semiautomatic firearms

Patent No. US8820211 (titled "Selectable dual mode trigger for semiautomatic firearms") on Jan 10, 2014. The application was issued on Sep 2, 2014.

’211 is related to the field of semi-automatic firearm trigger mechanisms, specifically those designed to increase the rate of fire through a pull-and-release cycle. It addresses the technical challenge of providing a selectable firing mode that allows a user to toggle between standard semi-automatic operation and a high-rate mode where a round is discharged upon both the rearward pull and the forward release of the trigger.

The underlying idea behind ’211 is the use of a selector cam to physically alter the timing and depth of the disconnector’s engagement with the hammer. By rotating an external lever, the user shifts a camming surface that tilts the primary disconnector, causing it to release the hammer prematurely during the trigger’s return stroke. This mechanical shift effectively converts the trigger release into a second firing event without requiring external add-ons or recoil-dependent hardware.

The claims of ’211 focus on a secondary disconnector mechanism designed to prevent the dangerous condition of hammer follow or unintentional automatic fire. This component acts as a fail-safe that captures the hammer whenever the trigger is held in a “central position”—a middle ground where neither the main trigger sear nor the primary disconnector is positioned to safely catch the hammer as the bolt cycles back into battery.

In practice, the invention functions by using a spring-biased auxiliary hook that monitors the trigger's orientation relative to a static point in the firearm, such as the safety selector. If the operator fails to fully pull or fully release the trigger, this secondary disconnector maintains a positive grip on the hammer. Only when the trigger completes its travel to the fully rearward or fully forward position does the secondary disconnector encounter a contact point that forces it to pivot and hand off the hammer to the appropriate primary sear.

This approach differentiates itself from prior “binary” triggers by integrating the selection mechanism directly into the trigger body and solving the reliability issues inherent in three-position trigger travel. By ensuring the hammer is always captured in the central position, the invention eliminates the risk of the hammer following the bolt forward and causing a malfunction or an unregulated discharge, thereby providing a high-rate system that remains mechanically predictable and safe.

How does this patent fit in bigger picture?

Technical Landscape

In the early 2010s when ’211 was filed, semi-automatic firearm trigger mechanisms were typically implemented using a single disconnector designed to capture the hammer after a discharge, ensuring only one round fired per trigger cycle. At a time when increasing the rate of fire commonly relied on external mechanical cranks or recoil-assisted stocks rather than internal fire-control modifications, hardware constraints made achieving a multi-shot cycle non-trivial without risking mechanical failures. Specifically, systems attempting to fire on both the pull and release of a trigger often faced the technical reality of hammer follow, where the hammer would fail to engage a sear and instead follow the bolt carrier forward, resulting in either a failure to fire or an uncontrolled discharge.

Prosecution Position

The disclosed invention represents a technical advancement through an architectural shift in the fire-control group that integrates a dual-disconnector system with a selectable cam interface. By incorporating a secondary disconnector specifically configured to engage the hammer when the trigger is in a central transition state, the design overcomes the technical constraint of hammer follow inherent in binary-action triggers. This structural solution enables a reliable dual-fire capability—discharging on both pull and release—while ensuring the hammer is mechanically captured if the trigger is improperly manipulated. The integration of a selector cam further allows for immediate transitions between standard semi-automatic and enhanced-rate modes without requiring the removal or installation of hardware.

Claims

The patent contains a total of 4 claims, with claim 1 serving as the sole independent claim. This independent claim focuses on an integral movable device for a firearm, specifically a spring-biased secondary disconnector designed to hold a pivotal hammer in a cocked position when the trigger is in a central state, preventing unintended release when primary sear surfaces are not engaged. The dependent claims serve to further define the mechanical assembly and operation of the device, specifying its attachment to the trigger via a pivot pin, its interaction with static firearm components, and the inclusion of a stop mechanism to ensure hammer release when the trigger returns to a fully forward position.

Key Claim Terms New

Definitions of key terms used in the patent claims.

Term (Source)	Support for Specification	Interpretation
Central position (Claim 1)	The secondary disconnector prevents the hammer from following the bolt assembly forward if the engagement surface of the trigger or the primary disconnector is not in position to retain hammer in a cocked rearward position. If the trigger is in a central position that would allow the hammer to follow the bolt forward, the secondary disconnector will engage hammer retaining it in a rearward position until the trigger is either pulled or released.	A specific intermediate trigger state located between the fully rearward (pulled) position and the fully forward (released) position where standard sear or primary disconnector engagements are not active.
Hammer engagement surface (Claim 1)	In one embodiment the invention comprises of the following core components: A trigger, a primary disconnector, a secondary disconnector, a hammer... The secondary disconnector [has] a hammer engagement surface which engages a corresponding engagement surface on said pivotal hammer.	A specific interface on the secondary disconnector designed to catch and hold a corresponding surface on the hammer to maintain a cocked state.
Hammer follow (Claim 1)	In the double fire mode, if the trigger is not manipulated properly, the hammer can follow the bolt assembly forward as it reciprocates resulting in either multiple rounds fired with one function of the trigger or the hammer being in a forward (fired) position with a loaded round in the chamber. The secondary disconnector prevents the hammer from following the bolt assembly forward if the engagement surface of the trigger or the primary disconnector is not in position. This eliminates the possibility of the hammer following the bolt forward, which would otherwise meet the definition of a machine gun.	A failure condition where the hammer fails to be captured in a cocked position and instead follows the bolt assembly forward, potentially causing unintended fire or a dead chamber.
In battery (Claim 1)	The secondary disconnector holds said pivotal hammer in the cocked position when the firearm's action is in battery until said trigger is pulled fully rearward from the central position. This prevents the hammer from following the bolt assembly forward as it reciprocates. This ensures the hammer is not in a forward (fired) position with a loaded round in the chamber.	The state of the firearm's action where the bolt or slide is fully forward and the chamber is closed, ready for firing.
Pivotal disconnector (Claim 1)	When the selector lever is turned, the selector cam engages the primary disconnector, tilting the primary disconnector on its axis, thus varying the amount of engagement of the primary disconnector on the hammer. In this mode, the primary disconnector engagement will not release hammer until the engagement surface of trigger or trigger mechanism is in position to retain hammer in a cocked position.	A rotating component (distinct from the secondary disconnector) that captures the hammer during the firearm's action cycle to prevent automatic fire, often referred to as the primary disconnector.
Secondary disconnector (Claim 1)	The secondary disconnector prevents the hammer from following the bolt assembly forward if the engagement surface of the trigger or the primary disconnector is not in position to retain hammer in a cocked rearward position. If the trigger is in a central position that would allow the hammer to follow the bolt forward, the secondary disconnector will engage hammer retaining it in a rearward position until the trigger is either pulled or released. The secondary disconnector greatly enhances the reliability of the trigger system, as well as prevents more than one round being fired per trigger function.	A spring-biased mechanical component that prevents 'hammer follow' by capturing and holding the hammer in a cocked position specifically when the trigger is in a central position between its fully pulled and fully released states.
Trigger sear surface (Claim 1)	In this mode, the primary disconnector engagement will not release hammer until the engagement surface of trigger or trigger mechanism is in position to retain hammer in a cocked position. The secondary disconnector prevents the hammer from following the bolt assembly forward if the engagement surface of the trigger or the primary disconnector is not in position to retain hammer in a cocked rearward position.	The primary mechanical engagement point on the trigger body intended to hold the hammer in a cocked position when the trigger is in the forward/released state.

Litigation Cases New

US Latest litigation cases involving this patent.

Case Number	Filing Date	Title
4:25-cv-00299	Jun 6, 2025	Abc Ip, Llc V. Harrison Gunworks Llc

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US8820211

Application Number: US14152894A
Filing Date: Jan 10, 2014
Publication Date: Sep 2, 2014
External Links: Slate, USPTO , Google Patents

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