Last Round Bolt Hold-Open Mechanism Automatic Release
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Solution Overview
Problem
Existing last round bolt hold-open mechanisms require additional manual steps to release the bolt after reloading, disrupting the operator's aim and firing position, and are prone to premature closure due to weapon movement or follower malfunctions.
Innovation Solution
A spring-biased bolt catch mechanism that automatically releases the bolt when a loaded magazine is inserted, relying on the presence or absence of ammunition rather than the follower's position, ensuring the bolt remains locked open until a new round is present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a manual release step is required after reloading, then the bolt can be securely held open, but the operator's aim and firing position are disrupted
Solution Approach 1:
The bolt catch mechanism automatically detects the magazine status and releases the bolt without requiring manual intervention. The system serves itself by using the magazine follower's position to trigger the release, eliminating the need for operator action and maintaining aim stability.
Solution Approach 2:
The mechanism uses feedback from the magazine follower's position to control bolt release. When the follower reaches a certain position indicating a loaded magazine, the system automatically triggers bolt release, creating a closed-loop control that ensures reliable operation without manual input.
2Device complexity
If the bolt catch is biased to return to unlocked position, then the mechanism is simple, but the bolt may close prematurely on an empty chamber
Solution Approach 1:
The bolt catch is pre-biased to remain engaged and prevent premature closure. The spring loading creates a default locked state that requires a specific trigger event (magazine follower position) to release, counteracting the natural tendency toward unlocked position and preventing accidental closure on empty chambers.
Solution Approach 2:
The spring-biased mechanism provides a cushioning force that maintains bolt catch engagement until properly released. This pre-loaded spring acts as a safety buffer, ensuring the bolt remains secured even under vibration or impact conditions that might otherwise cause premature release.
3Device complexity
If the bolt remains locked open after magazine removal, then the mechanism is simple, but an additional manual step is required to recharge
Solution Approach 1:
The mechanism performs preliminary preparation by automatically releasing the bolt as soon as a loaded magazine is detected. This advance action ensures the weapon is ready to fire immediately upon magazine insertion, eliminating the need for additional manual steps and reducing reloading time.
Solution Approach 2:
The system automatically manages the bolt release function by detecting magazine insertion and triggering release without operator intervention. This self-service capability eliminates the manual release step and reduces the time lost during the reloading process.
4Ease of operation
If a manual release button or lever is added, then the bolt can be released, but the device complexity increases
Solution Approach 1:
The mechanism eliminates the need for manual release buttons or levers by using the magazine follower's own motion to trigger bolt release. The system serves itself by converting the follower's positional change into the release action, removing additional components and simplifying the overall structure.
Solution Approach 2:
The magazine follower serves multiple functions: it feeds ammunition and simultaneously controls bolt release. By making the follower a multi-functional component, the design eliminates the need for separate release mechanisms, reducing device complexity while maintaining operational capability.
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 rapid return to a ready-to-fire state without manual intervention, maintaining weapon stability and preventing premature closure, even under impact or follower delays, thus enhancing operational reliability and accuracy.
Implementation Method 1
A spring-biased bolt catch mechanism that automatically releases the bolt when a loaded magazine is inserted
Data Source
AI summary
Provided is a last round bolt hold-open mechanism for a firearm with a removable ammunition magazine and a longitudinally reciprocating bolt that automatically releases the bolt when a loaded ammunition magazine is inserted. The mechanism includes a frame mountable to a firearm receiver and having a pair of mounting flanges. A catch member is pivotally mounted on a pivot axle oriented transverse to the longitudinal reciprocation of the bolt and carried by the mounting flanges. The catch member has a rearward portion that moves between bolt blocking and bolt release positions and is spring biased toward the bolt blocking position. A forwardly extending finger is configured to be lifted by the presence of at least one ammunition cartridge in the magazine and, when lifted, causes the catch member to pivot to the bolt release position.