Firearm trigger group module with pivoting element non-coaxial to assembly pin and method of installing a trigger group module
Patent No. US9835398 (titled "Firearm trigger group module with pivoting element non-coaxial to assembly pin and method of installing a trigger group module") on Mar 16, 2016. The application was issued on Dec 5, 2017.
What is this patent about?
’398 is related to the field of aftermarket fire control systems for firearms, particularly stamped-metal receivers like those found in AK-pattern rifles. In these firearms, the factory-drilled holes for the hammer and trigger pins are often imprecise or misaligned, which can cause traditional drop-in trigger units to bind, tilt, or require manual filing of sear surfaces to function correctly.
The underlying idea behind ’398 is to decouple the functional geometry of the fire control components from the potentially flawed geometry of the firearm receiver. By mounting the hammer and trigger to a self-contained internal frame using their own dedicated axes, the invention ensures that the critical relationship between the sear, disconnector, and hammer remains perfectly aligned regardless of how poorly the receiver's pin holes were drilled.
The claims of ’398 focus on a trigger group module where the internal frame is secured to the receiver using standard assembly pins, yet at least one of the primary components—either the hammer or the trigger—pivots on a transverse axis that is not coaxially aligned with those assembly pins. This allows the module to use the receiver's existing holes for mounting while maintaining its own independent, high-precision centers for rotation.
In practice, the module frame is dropped into the receiver and held in place by pins passing through the original factory openings. To accommodate this while maintaining the offset pivot point, the trigger member includes an oversized passageway that allows the mounting pin to pass through the component without touching it, ensuring the trigger only rotates around its own dedicated, factory-aligned axle within the module frame.
This approach differs from prior art by eliminating the need for custom gunsmithing or 'fitting' of drop-in units. Furthermore, the design incorporates adjustable set screws positioned to bear against the internal rivet heads of the trigger guard rather than the receiver floor itself, preventing the common issue of dimpling or deforming the thin stamped metal during installation.
How does this patent fit in bigger picture?
Technical Landscape
In the mid-2010s when ’398 was filed, fire control components for stamped-receiver firearms were typically implemented using individual parts that relied on the receiver walls themselves to provide the structural axes for rotation. At a time when aftermarket upgrades commonly utilized the existing assembly pin holes as the primary pivot points for hammers and triggers, system performance was highly dependent on the dimensional tolerances of the host firearm's chassis. When hardware constraints involved stamped metal components with potentially misaligned or imprecise pin placements, the installation of high-precision components was non-trivial, often requiring manual fitting or modification to ensure proper sear engagement and mechanical reliability.
Prosecution Position
The disclosed invention represents a technical advancement through an architectural shift from receiver-dependent components to a self-contained, frame-based fire control module. By decoupling the rotational axes of the hammer and trigger from the assembly pins that secure the module to the firearm receiver, the system overcomes the technical constraint of receiver dimensional imprecision. This integration ensures that critical mechanical interfaces, such as the relationship between the sear, disconnector, and hammer, remain fixed within a rigid internal housing regardless of external receiver tolerances. Furthermore, the inclusion of adjustment mechanisms within the module frame enables precise leveling and stabilization against the receiver floor, achieving a consistent trigger pull and reliable reset without requiring permanent modification to the firearm's primary structure.
Claims
This patent contains 28 total claims, with claims 1 and 15 serving as the independent claims. The independent claims focus on a modular firearm trigger group and its combination with a receiver, specifically featuring a frame that houses a hammer and trigger where at least one component axis is offset from the receiver's assembly pin openings. The dependent claims serve to further define the assembly by specifying the orientation and placement of set screws for securing the module, the inclusion of oversized passageways for pin clearance, and the use of spring-loaded mounting assemblies with guide channels to facilitate component removal.
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US9835398
- Application Number
- US15071300A
- Filing Date
- Mar 16, 2016
- Publication Date
- Dec 5, 2017
- External Links
- Slate, USPTO , Google Patents