Firearm Last Round Hold Open Lever Mechanism
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Solution Overview
Problem
Existing Last Round Hold Open (LRHO) mechanisms for firearms are unreliable due to inexpensive stamped metal construction, are large and cumbersome, interfere with other firearm components, and require removal for cleaning and maintenance, lacking durability and visual indication of emptiness.
Innovation Solution
A compact, durable LRHO apparatus comprising a first lever, second lever, mag stop, bolt catch, and magazine release, with components pivotally connected and embedded within the firearm's lower receiver to ensure accurate magazine height positioning and prevent interference, featuring a mag stop with bosses for backup functionality and a large magazine release for easy operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If existing LRHO mechanisms are made from stamped metal pieces to reduce cost, then manufacturing cost is reduced, but reliability and durability decrease
Solution Approach 1:
The patent employs composite construction by combining stamped metal components with machined aluminum alloy components. The LRHO arm, magazine release, and related parts are machined from aluminum alloy blocks, providing superior strength and reliability, while other components remain stamped for cost efficiency. This composite approach resolves the contradiction between manufacturing cost and reliability.
2Reliability
If LRHO mechanisms are made large to ensure functionality, then operational reliability is improved, but device compactness and ease of operation deteriorate
Solution Approach 1:
The LRHO mechanism is segmented into distinct functional components: the LRHO arm, magazine release button, spring assembly, and cam mechanism. Each component is optimized independently for its specific function, allowing the overall mechanism to be compact while maintaining reliability. The segmented design enables precise positioning and reduces interference with other firearm components.
Solution Approach 2:
The mechanism utilizes three-dimensional spatial arrangement within the magazine well area, positioning components vertically and horizontally to maximize space utilization. The LRHO arm pivots in a vertical plane while the magazine release operates horizontally, creating orthogonal motion paths that prevent interference and maintain compactness.
3Reliability
If LRHO mechanisms are integrated into firearm components, then functionality is improved, but ease of cleaning and maintenance deteriorates
Solution Approach 1:
The LRHO mechanism is designed as an extractable assembly that can be removed from the firearm as a unit. The entire LRHO assembly, including the arm, magazine release, and spring, can be extracted from the magazine well area for cleaning and maintenance, then reinstalled without disassembling other firearm components. This resolves the contradiction by providing maintenance accessibility while maintaining integrated functionality.
Data Source
AI summary
A last round hold open (LRHO) apparatus comprising a first lever having a first end and a second end; a second lever having a first end and a second end, the first end of the second lever in contact with the second end of the first lever; a bolt catch in contact with the second end of the second lever, and with a bolt carrier; and a follower in contact with the first end of the first lever, such that when the follower pushes up on the first end of the first lever, the second end of the first lever pushes down on the first end of the second lever, and the second end of the second lever pushes up on the bolt catch, resulting in activation of the bolt catch and opening the bolt carrier to alert an operator of the firearm that the firearm is out of ammunition.