Select-Fire Trigger Assembly for Open-Bolt Machine Guns
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Solution Overview
Problem
Machine guns lack a select fire function, which is necessary for operators to choose between semiautomatic and fully automatic fire, especially for open-bolt systems like the M240 machine gun.
Innovation Solution
A trigger assembly with a selector that allows operation between safe, semiautomatic, and fully automatic fire positions, incorporating a sear block to prevent inadvertent firing and a disconnector catch to reduce wear and prevent undesirable reconnecting of the sear link with the sear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a machine gun uses an open-bolt system without a selector, then the structure is simple and reliable, but the firearm lacks select fire capability (cannot choose between semiautomatic and fully automatic fire)
Solution Approach 1:
The trigger assembly is designed to perform multiple functions through a single integrated structure. The trigger member can engage with different positions on the sear (first position for semiautomatic, second position for fully automatic) and the selector switch controls the disconnector positioning. This multi-functional design allows the open-bolt machine gun to achieve select fire capability without requiring separate trigger assemblies for different fire modes.
Solution Approach 2:
The patent employs a nested arrangement where the disconnector is positioned within the trigger assembly, and the selector switch integrates with the sear and trigger member. The sear has multiple engagement positions that nest different firing modes within a single component structure. This nesting approach allows complex select fire functionality to be achieved without proportionally increasing overall device complexity.
2Reliability
If the trigger is blocked from moving in safe position, then safety is improved, but the sear must still be protected from inadvertent movement due to bolt impact
Solution Approach 1:
The sear block is positioned to preemptively prevent inadvertent sear movement before it can cause accidental discharge. When the trigger is blocked in safe position, the sear block occupies a position that physically prevents the sear from moving due to bolt impact or other disturbances. This preliminary protective action ensures safety without requiring the trigger assembly to be overly complex.
Solution Approach 2:
The sear block acts as an intermediary component between the bolt and the sear. Instead of allowing direct interaction between the bolt and sear that could cause inadvertent firing, the sear block mediates this interaction by positioning itself to prevent unwanted sear movement while still allowing proper engagement during intended firing operations.
3Device complexity
If the sear link can reconnect with the sear after firing, then the mechanism is simple, but wear increases and undesirable reconnecting may occur
Solution Approach 1:
The disconnector catch extracts or removes the sear link from potential reconnection with the sear after firing. The disconnector catch is positioned to engage with the sear link and prevent it from reconnecting with the sear, thereby eliminating the risk of wear and malfunction associated with repeated engagement and disengagement. This extraction approach simplifies the overall mechanism by preventing unnecessary movements.
Solution Approach 2:
The disconnector catch performs a preliminary action by positioning itself to prevent sear link reconnection before wear or malfunction can occur. By establishing this preventive positioning early in the firing cycle, the mechanism avoids the cumulative damage that would result from repeated engagement and disengagement of the sear link with the sear.
Data Source
AI summary
A trigger assembly includes a selector operable between a safe position, a semiautomatic fire position, and an automatic fire position. In one example, the assembly includes a trigger rotatable between a resting position and a pulled position, a disconnector pivotable between a first position where it is in the path of the operational rod, and a second position where it is out of the path of the operational rod. A sear is pivotable between an engaged position and a disengaged position and is biased to the engaged position where it is positioned in the path of the operational rod. A sear link is pivotably connected to the trigger, such that pulling the trigger moves the sear link into contact with the sear to pivot the sear towards the disengaged position. The sear link is spaced from the sear when the trigger is in the resting position.