M249 Trigger Assembly Select Fire Mechanism
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Solution Overview
Problem
The M249 machine gun lacks a select fire mechanism, forcing operators to choose between fully automatic and semi-automatic modes, which is not always desirable or necessary.
Innovation Solution
A trigger assembly with a sear pivotally mounted to a trigger housing, including a disconnector and a select fire mechanism with a switch accessible outside, allowing the rifle to be selectively operated in fully automatic or semi-automatic modes by moving a lever between fully-automatic and semi-automatic selector surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the M249 is equipped with a standard trigger assembly for fully automatic fire, then the rifle can provide continuous automatic fire capability, but it cannot provide semi-automatic single-shot capability
Solution Approach 1:
The trigger assembly is designed to perform multiple functions by incorporating a select fire mechanism that allows the same assembly to enable both fully automatic and semi-automatic firing modes. The selector switch and associated mechanism allow the trigger assembly to adapt its function based on the selected mode, eliminating the need for separate trigger assemblies for different firing modes.
Solution Approach 2:
The trigger assembly incorporates movable components including a selector switch that can be positioned in different locations (fully automatic or semi-automatic positions). This dynamic configuration allows the assembly to change its operational characteristics based on the selector position, enabling versatility without requiring multiple static assemblies.
2Loss of substance
If the M249 operates in fully automatic mode continuously, then rapid fire capability is maintained, but unnecessary ammunition is expended when single-shot capability is needed
Solution Approach 1:
The selector switch allows the operator to pre-select the desired firing mode before engaging the trigger. By setting the selector to semi-automatic position when single-shot capability is needed, the operator prevents unnecessary ammunition expenditure before the firing sequence begins, rather than attempting to control the mode during or after firing.
3Adaptability or versatility
If a select fire mechanism is added to the M249 trigger assembly, then firing mode versatility is enabled, but the device complexity increases
Solution Approach 1:
The select fire mechanism is merged with the existing trigger assembly components rather than being implemented as a separate, independent system. The selector switch, disconnector, and sear modifications are integrated into the trigger assembly structure, combining the select fire function with the existing firing mechanism to minimize additional complexity.
Solution Approach 2:
The disconnector serves as an intermediary component that mediates between the selector switch and the sear mechanism. When the selector is in the semi-automatic position, the disconnector prevents the sear from remaining engaged, thereby controlling the firing mode through this intermediate component rather than requiring direct modification of the sear or trigger mechanism.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the M249 rifle to be operated in either fully automatic or semi-automatic modes, providing flexibility and reducing unnecessary ammunition expenditure by allowing single-shot capability when desired.
Implementation Method 1
A sear spring of the trigger assembly biases the sear to pivot to position the sear tip in the path of the op rod assembly
Implementation Method 2
A disconnector spring biases the disconnector toward the sear and the selector body
Implementation Method 3
expanding gases from the ignition of powder in the cartridge furnish the energy for the continued fully automatic operation
Data Source
AI summary
A trigger assembly for a trigger housing for a, M249 fully automatic rifle is provided having a switch accessible at the outside of the trigger housing for changing the firing of the rifle between semi-automatic and fully-automatic fire.