Firearm Breech Bolt Lug Tapering for Jam Prevention
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Solution Overview
Problem
Automatic and semi-automatic firearms with gas-operated breech bolt carrier systems often experience jamming due to misalignment of bolt lugs with receiver lugs, reducing weapon reliability and necessitating frequent maintenance.
Innovation Solution
The breech bolt assembly features a lug portion with tapering outer and side faces, allowing the lugs to align and rotate properly with receiver lugs, preventing jamming by ensuring correct alignment and smooth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bolt lugs with parallel faces are used, then the structure is simple and easy to manufacture, but the bolt lugs become misaligned with receiver lugs causing jamming
Solution Approach 1:
The bolt lugs are designed with asymmetric tapering where the forward face has a different angle than the rearward face. This asymmetric geometry creates a self-aligning mechanism that guides the bolt lugs into proper alignment with receiver lugs during the firing cycle, eliminating the jamming problem while maintaining structural simplicity
Solution Approach 2:
The lug geometry parameters are changed from parallel faces to tapered faces with specific angle measurements. The forward face taper angle and rearward face taper angle are optimized to work together with receiver lug geometry, transforming the alignment problem into a geometric solution that ensures reliable meshing
2Strength
If bolt lugs are made with larger contact area, then the strength increases, but the alignment precision with receiver gaps decreases
Solution Approach 1:
The lug design implements local quality by having different face characteristics - the forward face uses a taper angle optimized for alignment guidance, while the rearward face uses a different taper angle optimized for strength and load distribution. This localized optimization allows the lug to simultaneously achieve both alignment precision and contact strength
3Speed
If the bolt moves forward quickly to chamber cartridge, then the cycling speed increases, but the alignment between bolt lugs and receiver lugs becomes inaccurate causing misalignment
Solution Approach 1:
The tapered lug geometry performs preliminary alignment action during the approach phase of bolt movement. As the bolt moves forward, the taper angles guide the lugs into correct alignment with receiver lugs before full contact is made, ensuring accurate meshing even at high cycling speeds where precision might otherwise be compromised
Data Source
AI summary
A firearm including a receiver, a barrel, a breech bolt assembly, and a trigger assembly. The bolt assembly has a bolt including a body portion, a lug portion, and a firing pin bore. The lug portion includes outward extending lugs, a cartridge recess, and an off-center hole. The bolt assembly also includes an extractor and an ejector pin. At least some of the lugs on the lug portion of the bolt have a tapering outer face so that a rearward face of the respective lug is taller than a forward face of the respective lug. In another aspect, at least some of the lugs on the lug portion of the bolt have tapering side faces so that a rearward face of the respective lug is wider than a forward face of the respective lug.