Auto Sear Trip Link for Compact AR Firearms
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Solution Overview
Problem
Compact AR-platform firearms with shortened bolt carriers are unable to trip the auto sear without significant modification, as existing solutions require attachment to the upper receiver or complex linkage devices.
Innovation Solution
An auto sear trip link that is independent of both upper and lower receivers, featuring laterally spaced longitudinally extending members with a forward portion resting on the lower receiver and a rearward portion supported by the auto sear, includes an engagement horn and rear crossmember to interface with the bolt carrier, allowing the bolt carrier to trip the auto sear as it reaches the in-battery position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a shortened bolt carrier is used in compact firearms, then the firearm becomes more compact and eliminates the need for an extension to house the recoil spring, but the bolt carrier is unable to trip the auto sear
Solution Approach 1:
A trip link is introduced as an intermediary component between the bolt carrier and auto sear. The trip link includes a forward portion that interfaces with the bolt carrier boss and a rearward portion that engages the auto sear, mediating the force transmission from the shortened bolt carrier to the auto sear to enable tripping without requiring the bolt carrier to extend beyond the upper receiver
Solution Approach 2:
The trip link utilizes lateral spacing between the longitudinally extending members to fit within the available space between the lower receiver sidewalls and upper receiver edges, creating a three-dimensional solution that accommodates the compact configuration while maintaining the necessary mechanical linkage
2Ease of operation
If existing solutions with lost motion linkage devices are used, then the auto sear can be tripped, but the upper receiver requires modification with elongated grooves or channels
Solution Approach 1:
The trip link serves as a self-contained intermediary mechanism that brings the tripping function to the bolt carrier rather than requiring modifications to the upper receiver. The linkage device includes all necessary components (longitudinally extending members, engagement horns, crossmembers) integrated into a single assembly that interfaces with existing features
Solution Approach 2:
The trip link is divided into distinct functional segments: longitudinally extending members for structural support, engagement horns for interfacing with the bolt carrier boss, and rear crossmembers for engaging the auto sear. This segmentation allows each component to be optimized for its specific function while maintaining manufacturability
3Ease of operation
If a trip bar carried within the upper receiver is used, then the auto sear can be tripped, but the device complexity increases with integration into an elongated structure
Solution Approach 1:
The trip link is designed to fit within the standard AR-15 lower receiver fire control compartment without requiring integration into a custom elongated structure. The longitudinally extending members utilize the existing space between the lower receiver sidewalls and upper receiver edges, making the solution universally applicable to standard configurations
Solution Approach 2:
The trip link employs a lightweight construction with thin-walled longitudinally extending members that provide sufficient structural rigidity while minimizing material usage. The engagement horns and crossmembers are designed as thin, precisely-formed features that reduce overall complexity while maintaining functional integrity
Data Source
AI summary
Disclosed is a mechanism for use with firearms having compact bolt carrier designs without modification of or connection to either the upper or lower receiver. It provides an auto sear trip linkage that is independent of both the upper and lower receivers and which may be used as a “drop in” unit to allow an upper receiver assembly otherwise configured for semi-automatic fire to be used in full-auto mode with a standard, full-auto capable AR-pattern lower receiver.