Cotter Pin Anti-Rotation Mechanism for AR-15 Bolt Assembly

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Solution Overview

Problem

Existing cotter pins in AR-15 and M16 firearms tend to rotate during bolt travel, leading to wear on the firing pin.

Innovation Solution

An anti-rotation mechanism using a chamfered hole in the bolt and a standard AR15/M16 cotter pin, combined with a notch feature on the firing pin, prevents rotation by seating the cotter pin head within a recessed channel on the receiver plate, reducing wear and maintaining the firing pin's position.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a standard cotter pin is used to hold the firing pin, then the firing pin can be retained in position, but the cotter pin rotates during bolt travel causing wear on the firing pin

Engineering Contradiction:

Improvefiring pin position retentionVSAvoidcotter pin rotation and wear

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The bolt is given an asymmetric geometry with a chamfered hole at a specific angular position. This asymmetric feature interacts with the cotter pin to create a non-rotating mounting arrangement, preventing the cotter pin from rotating during bolt travel while maintaining secure retention of the firing pin.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The solution introduces a new geometric dimension by adding a chamfered hole at a specific angular position on the bolt. This dimensional feature (the chamfered hole at a particular angle) creates an anti-rotation mechanism that constrains the cotter pin's movement, preventing rotation while allowing the bolt to reciprocate.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If the cotter pin is allowed to rotate freely, then assembly is simple, but wear occurs on the firing pin and reliability decreases

Engineering Contradiction:

Improveassembly simplicityVSAvoidfiring pin retention and wear resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The asymmetric chamfered hole design maintains ease of assembly while preventing rotation. The chamfered hole is positioned at a specific angular location that naturally guides the cotter pin into the correct orientation during assembly, eliminating the need for complex alignment procedures while ensuring reliable non-rotating retention.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The chamfered hole configuration allows the cotter pin to self-align and self-constrain during assembly and operation. The geometry of the chamfered hole automatically prevents rotation without requiring additional adjustment or complex mechanisms, maintaining simplicity while ensuring reliability.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS8316755B2Cotter pin anti rotation mechanism for accommodating sub caliber ammunition utilized in an AR-15 type firearm

Publication Date: 2012.11.27 22 EVOLUTION

AI summary

An anti-rotation feature incorporated between a cotter pin and a sub caliber action device installable within an upper receiver of a firearm. A receiver plate exhibits a notched interior for seating a bolt in reciprocating fashion. A chamfer formed in a side of the bolt intersects a length extending channel of the bolt for seating within the notched interior. The chamfer seating a head of the cotter pin to prevent rotation during bolt travel. A rearward support sleeve seats an opposing guide rod associated with the receiver plate and in order to maintain the bolt assembly. A firing pin exhibits a notch at a location along its shaft and, upon installation within an interior aperture of the bolt, is retained in position by the cotter pin. The firing pin is configured so as to exhibit a reduced diameter end projection upon which is supported a coil spring.