Two-Stage Drop-In Trigger Assembly for M4/M16 Compliance
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Solution Overview
Problem
Current two-stage drop-in trigger assemblies for M4/M16 firearms are not compliant with the European Standard, which requires the safety selector to be able to be set to the 'SAFE' position when the hammer is in the upright or 'as fired' condition, and existing solutions either prevent this or are single-stage and non-adjustable.
Innovation Solution
A novel two-stage, drop-in trigger assembly design that allows the safety selector to be engaged and the hammer to be recocked with the safety selector in the 'SAFE' position, featuring a front hook that can rotate to allow the hammer to move out of the way, and a sear surface relocation to reduce manufacturing tolerance sensitivity, along with a disconnector spring for stability under shock loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a traditional two-stage trigger assembly is used for M4/M16 firearms, then the trigger pull characteristics are improved (two-stage operation), but the safety selector cannot be set to SAFE position when the hammer is in the upright position (non-compliance with European Standard)
Solution Approach 1:
The trigger assembly is divided into separate functional components: a trigger group and a hammer group that can be independently positioned. The hammer group includes a pivot bushing that allows the hammer to be positioned in either a forward upright position or a rearward cocked position, enabling the safety selector to function properly while maintaining two-stage trigger operation.
Solution Approach 2:
A pivot bushing acts as an intermediary component between the hammer and the receiver, providing a pivot axis that enables the hammer to rotate between upright and cocked positions. This intermediary mechanism allows the safety selector to engage properly when the hammer is in the upright position, thereby achieving European Standard compliance while preserving two-stage trigger functionality.
2Adaptability or versatility
If the hammer is kept in the upright position to allow safety selector engagement, then compliance with European Standard is achieved, but the trigger must be depressed to prevent hammer recocking (compromising two-stage operation)
Solution Approach 1:
The hammer is designed with dynamic positioning capability through the pivot bushing, allowing it to rotate between a forward upright position (for safety engagement) and a rearward cocked position (for two-stage operation). This dynamic adjustment enables the system to switch between compliance mode and operational mode as needed.
Solution Approach 2:
The hammer positioning is extended into a rotational dimension, where the hammer can pivot around an axis defined by the pivot bushing. This adds a rotational degree of freedom that allows the hammer to occupy different spatial positions (upright vs. cocked) without interfering with either safety selector engagement or two-stage trigger operation.
3Adaptability or versatility
If a single-stage trigger assembly is used to allow safety selector engagement with upright hammer, then compliance with European Standard is achieved, but the trigger pull requires considerable pressure and exhibits creep (loss of two-stage characteristics)
Solution Approach 1:
The trigger assembly is segmented into distinct functional groups: the trigger group maintains two-stage operation through its internal geometry and spring arrangement, while the hammer group provides independent positioning capability. This segmentation allows each subsystem to optimize its function without compromising the other.
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 compliance with the European Standard by allowing the safety selector to be set to 'SAFE' with the hammer in the upright position without requiring the trigger to be depressed, reducing manufacturing tolerance sensitivity and minimizing 'trigger slap' during reload cycles.
Implementation Method 1
The hammer spring applies a torque to the hammer which develops a force at this radius
Implementation Method 2
A disconnector spring for stability under shock loads
Data Source
AI summary
A trigger assembly for a firearm is disclosed wherein the firearm includes a receiver, a safety selector and a hammer. The trigger assembly includes a trigger having a pivot axis, a front hook which is constructed and arranged to move with trigger rotation, a rear hook which is cooperatively arranged with the front hook and a spring which is positioned between the front hook and the rear hook. The front hook and the trigger are constructed and arranged relative to the safety selector and relative to the hammer in order to allow the hammer to be recocked from an upright position with the safety selector in a “SAFE” position. This particular construction provides a trigger assembly which is constructed and arranged as a two-stage, drop-in trigger assembly which is compliant with the European Standard for an M4/M16 (AR) platform.