Derivative works — US Patent 9151557

Defensive Disclosure for U.S. Patent 9,151,557: "Automatic Sear Assembly for a Rifle"

Publication Date: May 10, 2026

Subject: This document discloses novel and obvious variations of the automatic sear assembly described in U.S. Patent No. 9,151,557 (hereinafter '557). The purpose is to place these variations in the public domain, thereby establishing prior art against future patent applications for similar inventions. The following disclosures are based on the core principles taught in the '557 patent and represent foreseeable modifications and applications by a person having ordinary skill in the art (PHOSITA).

Derivative Concepts Based on Claim 1

Claim 1 describes an automatic sear assembly with a sear, a sear lever, and two springs sharing a common rotational axis, where the lever can either rotate independently or actuate the sear based on the direction of force applied by the bolt carrier.

1.1. Material & Component Substitution

Derivative 1.1.1: Polymer-Based Sear Lever with Embedded Wear-Resistant Insert

Enabling Description: The sear lever (200) is injection-molded from a high-impact, low-friction polymer such as glass-filled PEEK (Polyether ether ketone) or carbon-fiber-reinforced Nylon 6/6. At the point of contact with the bolt carrier (920), a metallic (e.g., S7 tool steel or tungsten carbide) or ceramic (e.g., silicon nitride) insert is co-molded or press-fit into the upper portion (210) of the lever. This composite construction reduces the overall reciprocating mass, thereby lowering the cyclic rate and improving controllability in full-automatic fire, while maintaining high durability at the critical wear surface. The first spring (300) is recalibrated to a lower spring rate to account for the reduced mass of the polymer lever, ensuring proper return to the reset position.
```
graph TD;
    A[Bolt Carrier 920] --/Forward Motion/--> B{Sear Lever 200};
    B --/Impacts/--> B1(Wear-Resistant Insert: Tungsten Carbide);
    B --/Composed of/--> B2(Body: Carbon-Fiber Nylon);
    B --/Pivots on/--> C[Pin 600];
    B --/Transfers Torque to/--> D[Automatic Sear 100];
    E[Spring 300 - Lower Rate] --/Biases/--> B;
```

Derivative 1.1.2: Magnetorheological Fluid Damper for Sear Return

Enabling Description: The first spring (300) is replaced with a miniature, sealed magnetorheological (MR) fluid damper. The damper's housing is fixed relative to the sear (100), and its actuator is linked to the sear lever (200). An embedded microcontroller, connected to a sensor on the selector switch (930), varies the viscosity of the MR fluid by applying a magnetic field. In semi-automatic mode, the fluid is set to high viscosity, preventing the sear lever from resetting quickly enough to engage the sear for a subsequent shot. In automatic mode, the fluid is set to low viscosity, allowing rapid, spring-like return of the lever. This provides for an electronically-controlled, "solid-state" fire control group with no change to the mechanical springs.
```
sequenceDiagram
    participant User as User
    participant SelectorSwitch as Selector Switch (930)
    participant Microcontroller as MCU
    participant MR_Damper as MR Damper
    participant SearLever as Sear Lever (200)

    User->>SelectorSwitch: Selects "Auto" Mode
    SelectorSwitch->>MCU: Signals "Auto"
    MCU->>MR_Damper: Applies Low/No Mag Field (Low Viscosity)
    loop Firing Cycle
        SearLever->>MR_Damper: Compresses Damper (Rearward)
        MR_Damper-->>SearLever: Exerts Low Damping Force
        SearLever-->>SearLever: Rapidly Returns (Forward)
    end
```

1.2. Operational Parameter Expansion

Derivative 1.2.1: Cryogenic Operation Assembly

Enabling Description: For operation in extreme cold environments (-60°C and below), all components are fabricated from a nickel-cobalt alloy such as MP35N, which retains its ductility and fatigue resistance at cryogenic temperatures, preventing brittle fracture. The standard springs (300, 400) are replaced with springs made from Elgiloy, a cobalt-chromium-nickel alloy known for its stability in extreme temperature ranges. All rotational interfaces between the pin (600), bushing (500), sear (100), and lever (200) are coated with a dry film lubricant like tungsten disulfide (WS2), which does not freeze or increase in viscosity like hydrocarbon-based lubricants.
```
graph TD
    subgraph Cryo-Assembly
        A[Sear - MP35N]
        B[Sear Lever - MP35N]
        C[Springs - Elgiloy]
        D[Pin/Bushing - MP35N w/ WS2 Coating]
    end
    E(Environment: -60°C) --> Cryo-Assembly
    Cryo-Assembly -- Functions Reliably --> F(Prevents Brittle Fracture)
```

Derivative 1.2.2: High-Frequency, Low-Mass Solenoid Actuator

Enabling Description: This variation is designed for a theoretical electrically-fired weapon system operating at extremely high cyclic rates (>2000 rounds/minute). The entire mechanical sear assembly is miniaturized using micro-electro-mechanical systems (MEMS) fabrication techniques. The sear lever (200) is replaced by a micro-machined silicon cantilever. The reciprocating bolt carrier's motion is detected by an optical sensor, which triggers a high-speed piezoelectric or solenoid actuator to trip a micro-sear. The "bidirectional articulation" is achieved electronically; the control logic ignores the rearward-pass sensor signal and only actuates on the forward-pass signal, mimicking the one-way mechanical action of the '557 patent.
```
stateDiagram-v2
    [*] --> Ready_to_Fire
    Ready_to_Fire --> Firing : Trigger Pulled
    Firing --> Rearward_Stroke : Cartridge Fires
    Rearward_Stroke --> Forward_Stroke : Bolt Reverses
    Forward_Stroke --> Firing : Optical Sensor & Piezo Actuator Trip Micro-Sear
    Firing --> Ready_to_Fire : Trigger Released
    Rearward_Stroke: Optical Sensor detects pass (ignored)
    Forward_Stroke: Optical Sensor detects pass (triggers actuator)
```

1.3. Cross-Domain Application

Derivative 1.3.1: Aerospace - High-Cycle Latching Mechanism for Deployable Structures

Enabling Description: The core principle of a biased, trip-able lever is adapted for a satellite's deployable solar array or antenna. The "sear" (100) becomes a primary latch holding a spring-loaded boom in its stowed position. The "bolt carrier" (920) is replaced by a cam on a rotating deployment shaft. As the shaft rotates, the cam deflects the "sear lever" (200) harmlessly in one direction. Upon a specific command or further rotation, the cam engages the lever from the opposite direction, causing it to trip the primary latch and release the boom. This provides a reliable, low-power, and resettable release mechanism for repeated deployment/stowing cycles. The bidirectional feature prevents accidental release during initial system checks when the cam might oscillate.
```
flowchart LR
    subgraph Stowed
        A[Deployment Motor Off] --> B(Cam Stationary);
        C[Primary Latch / Sear] -- Engaged --> D[Solar Array Boom];
        E[Trip Lever / Sear Lever] -- Biased --> C;
    end
    subgraph Deploying
        F[Motor On] --> G{Cam Rotates};
        G -- 1. Reverse Check --> H[Lever Deflects, No Release];
        G -- 2. Forward Deploy --> I[Lever Trips Latch];
        I --> J((Array Released));
    end
    Stowed --> Deploying;
```

Derivative 1.3.2: Agricultural Technology - Automated Seed Sorter/Ejector

Enabling Description: In a high-speed seed sorting machine, seeds travel on a conveyor belt. An optical sensor identifies an off-spec seed. This triggers an actuator which momentarily extends a "trip rod" (acting as the "bolt carrier") into the path of a sear lever. The sear lever, upon being tripped, releases a spring-loaded hammer that strikes a small pneumatic valve. The resulting puff of air ejects the single off-spec seed from the conveyor. As the trip rod retracts, a spring biases the lever back against the sear, which has been reset by a separate cam mechanism, readying the system for the next ejection event. The one-way action ensures the mechanism only fires on the actuator's extension stroke, not the retraction.
```
sequenceDiagram
    participant Sensor
    participant Actuator
    participant SearLeverAssembly
    participant PneumaticValve

    Sensor->>Actuator: Off-spec seed detected
    activate Actuator
    Actuator->>SearLeverAssembly: Extend Trip Rod
    activate SearLeverAssembly
    SearLeverAssembly->>PneumaticValve: Trip Sear, release hammer
    deactivate SearLeverAssembly
    activate PneumaticValve
    PneumaticValve->>PneumaticValve: Eject Air Puff
    deactivate PneumaticValve
    Actuator->>Actuator: Retract Trip Rod
    deactivate Actuator
```

Derivative 1.3.3: Consumer Electronics - Haptic Feedback Actuator

Enabling Description: The assembly is miniaturized and integrated into a game controller or VR glove to provide a sharp, mechanical "click" sensation. The "hammer" (940) is a weighted plunger that strikes the inside of the device's casing. The "bolt carrier" (920) is a small, motor-driven cam. When a haptic event is commanded by software, the motor spins the cam, which trips the sear lever (200), releasing the weighted plunger to create a distinct tactile impulse. The sear lever's bidirectional articulation allows the motor to spin continuously or oscillate without causing multiple unintended actuations, providing a single, clean "shot" of feedback per intended event. The first spring (300) ensures the mechanism is immediately ready for the next haptic signal.
```
graph TD
    A[Haptic Signal Received] --> B{Motor Rotates Cam};
    B --"Trips"--> C[Sear Lever];
    C --"Releases"--> D[Spring-loaded Plunger/Hammer];
    D --"Strikes Casing"--> E(Tactile Feedback Felt by User);
    F[Reset Spring] --"Resets"--> C;
    F --"Resets"--> D;
```

1.4. Integration with Emerging Tech

Derivative 1.4.1: AI-Optimized Fire Control

Enabling Description: The sear assembly is instrumented with a piezoelectric sensor on the sear lever (200) to measure the precise impact force and timing from the bolt carrier (920), and a strain gauge on the pin (600) to measure shear stress. Data is fed to an onboard edge AI processor. The AI model, trained on thousands of firing cycles under various conditions (temperature, ammunition type, fouling), dynamically controls a variable-force buffer system. It adjusts the buffer resistance in real-time to ensure the bolt carrier's velocity is optimal for consistent sear trip timing, minimizing component wear and maximizing reliability. The system can predict imminent part failure based on anomalous sensor readings.
```
graph TD
    subgraph Firearm
        A[Bolt Carrier] --Impacts--> B[Sear Lever w/ Piezo Sensor];
        B --> C[Automatic Sear];
        C --> D[Hammer];
        B --Pivots on--> P[Pin w/ Strain Gauge];
    end
    subgraph AI_FCS
        B --Force/Time Data--> E[Edge AI Processor];
        P --Shear Stress Data--> E;
        E --Analyzes & Predicts--> F[Control Signals];
        F --> G[Variable-Force Buffer System];
    end
    G --Adjusts Resistance--> A;
```

Derivative 1.4.2: IoT-Enabled Component Lifecycle Management

Enabling Description: The sear (100), sear lever (200), and pin (600) are embedded with passive RFID tags or a single low-power System-on-a-Chip (SoC) that includes an accelerometer and a counter. Each time the assembly cycles, the accelerometer detects the characteristic motion profile and increments a counter stored in non-volatile memory. Periodically, or when queried by a reader (e.g., in an armorer's depot), the device transmits its unique ID and total cycle count via a near-field communication (NFC) or Bluetooth Low Energy (BLE) protocol. This allows for precise, condition-based maintenance and lifecycle tracking of critical fire-control components, rather than relying on estimated round counts.
```
classDiagram
    class AutomaticSearAssembly {
        +String uniqueID
        +int cycleCount
        +accelerometer
        +nfc_ble_transceiver
        +nonVolatileMemory
        +incrementCounter()
        +transmitData()
    }
    class ArmorerReader {
        +readData(AutomaticSearAssembly)
        +logMaintenance()
    }
    class MaintenanceDatabase {
        +updateRecord(uniqueID, cycleCount)
    }
    ArmorerReader ..> AutomaticSearAssembly : queries
    ArmorerReader ..> MaintenanceDatabase : updates
```

Derivative 1.4.3: Blockchain-Verified Provenance and Firing Record

Enabling Description: Building on the IoT concept (1.4.2), the SoC in the sear assembly cryptographically signs each firing event record (comprising a timestamp, cycle number, and unique component ID). This data is transmitted to a secure receiver, which batches and records the transactions on a private, permissioned blockchain. This creates an immutable, auditable log of the firearm's usage history. The provenance of the sear assembly itself, from manufacturing (compliant with MIL-W-13855) to installation, is also recorded on the blockchain, ensuring supply chain integrity and preventing the use of counterfeit or uncertified parts.
```
sequenceDiagram
    participant SearAssembly as "Sear Assembly (SoC)"
    participant SecureReceiver as "Armory Receiver"
    participant Blockchain as "Parts & Usage Ledger"
    SearAssembly->>SearAssembly: Firing event detected
    SearAssembly->>SearAssembly: Sign event data(Timestamp, ID, Count)
    SearAssembly->>SecureReceiver: Transmit signed data
    SecureReceiver->>Blockchain: Batch & Write Transaction
    Blockchain-->>SecureReceiver: Confirm Write
```

1.5. The "Inverse" or Failure Mode

Derivative 1.5.1: Fail-Safe Disconnector Sear

Enabling Description: The automatic sear (100) is redesigned as a two-piece component, held together by a calibrated shear pin. The lower part of the sear interfaces with the hammer (940), while the upper part interfaces with the sear lever (200). In the event of a catastrophic failure, such as a "runaway" full-auto condition caused by a stuck component, a sensor detects an abnormally high cyclic rate. It triggers a small pyrotechnic or solenoid actuator that applies a lateral force to the two-piece sear, breaking the shear pin. The upper part of the sear then moves out of alignment, preventing the sear lever from imparting any further torque. This mechanically disables the automatic function, forcing the rifle into a single-shot or inoperable state, preventing further danger.
```
graph TD
    subgraph Normal_Operation
        A[Sear Lever] --> B(Upper Sear);
        B --"Shear Pin"--> C(Lower Sear);
        C --> D[Hammer];
    end

    subgraph Failure_Mode
        E[Runaway Condition Detected] --> F{Actuator Fires};
        F --"Breaks"--> G(Shear Pin);
        B -.-> C;
        H(Upper Sear Misaligned);
        A -."No Engagement".-> H;
    end
```

Derivative 1.5.2: Limited-Functionality Training Assembly

Enabling Description: A training version of the assembly is produced where the automatic sear (100) is made from a soft, brightly colored polymer (e.g., Delrin or Acetal) and the sear lever (200) is made of a standard metal. After a pre-determined number of cycles (e.g., 500), the metal lever will have physically abraded the polymer sear's contact surface (112) to the point where it can no longer be tripped. This provides a tangible, non-resettable, and easily inspectable service life limit for training or simulation firearms, ensuring they cannot be used indefinitely or converted to live-fire without replacing the visibly worn training sear. The spring forces would be tuned to allow function only with blank-firing or simulated-recoil training bolt carriers.
```
stateDiagram-v2
    [*] --> New
    New: Sear surface (112) intact
    New --> In_Use: First Firing Cycle
    state In_Use {
        [*] --> Cycling
        Cycling --> Cycling: Bolt carrier cycles, abrades sear surface
        state "Cycles: 0-499" as S1
        state "Cycle: 500" as S2
    }
    In_Use --> Worn_Out: After 500 cycles
    Worn_Out: Sear surface (112) abraded, no longer catches lever.
    Worn_Out: Automatic function disabled.
```

Combination Prior Art Scenarios

1. Integration with Open-Source 3D-Printed Receiver (e.g., "Are We Cool Yet?" or "Defense Distributed" designs):

Scenario: The automatic sear assembly of '557 is adapted for use in a 3D-printed lower receiver based on publicly available CAD files. The pin (600) and bushing (500) dimensions are modified to fit the tolerances and material properties of FDM-printed polymers like PLA+ or glass-filled nylon. The pin holes in the printed receiver are designed to accept heat-set threaded inserts, and the pin (600) is replaced with a threaded shoulder bolt that screws into the inserts, providing a more secure and durable mounting point in the polymer material than a simple press-fit pin. This combination makes the selective-fire mechanism accessible to custom, user-manufactured firearm platforms.

2. Integration with Arduino-based Fire Control Unit:

Scenario: The mechanical safe/fire selector switch (930) is replaced by a digital, multi-position switch connected to an Arduino Nano or similar microcontroller. The microcontroller directly controls a micro-servo or solenoid that physically blocks or unblocks the rotation of the automatic sear (100) at its arm portion (140), replicating the function of the selector switch cam. The open-source Arduino IDE is used to program custom fire-control modes, such as a variable burst mode (e.g., 2, 3, 4, 5 rounds) or a "binary" mode, all by manipulating the engagement of the '557 patent's core mechanical assembly via simple electronic control. The firmware for this controller is published under a GPL license.

3. Integration with Open-Standard Smart-Rail Communication Protocol (e.g., hypothetical MIL-STD-1913-ELEC):

Scenario: A future "smart" Picatinny rail standard (MIL-STD-1913-ELEC) is developed with an open-source data and power protocol. The '557 sear assembly is modified to include a micro-solenoid that can lock the sear lever (200) and prevent it from tripping the sear (100), even in the "auto" position. This solenoid is controlled by a grip or accessory mounted to the smart rail. Using the open protocol, an authorized user's biometric scanner on the grip can communicate with the sear assembly, enabling the automatic-fire capability only when the authenticated user is holding the weapon. This combines the mechanical invention of '557 with a standardized, open electronic authentication protocol for a "smart gun" application.