Metal-Core Polymer Projectile with Graduated Driving Bands
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Solution Overview
Problem
The use of polymer jackets in projectiles is hindered by radial slippage issues due to material dissimilarity with metal cores, leading to inaccuracy and increased wear on firearm components, and traditional solutions like soldering are impractical for solid metal cores.
Innovation Solution
A polymer jacketed projectile with radial driving bands of increasing thickness and high-friction surfaces on the core to ensure synchronized spinning, combined with a high-temperature polymer that reduces wear and maintains ballistic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polymer jacket is used with metal core, then cost is reduced and barrel wear is minimized, but radial slippage occurs causing inaccuracy
Solution Approach 1:
The polymer jacket is segmented into multiple radial driving bands of varying thicknesses rather than a uniform structure. This segmentation allows different portions of the jacket to engage the rifling at different rates, compensating for the material dissimilarity between polymer and metal core, and preventing radial slippage while maintaining accuracy.
Solution Approach 2:
The driving bands are designed with non-uniform thickness distribution, where each band has a specific local thickness optimized for its position in the jacket. This local quality variation ensures that the polymer jacket engages the rifling progressively from the front, synchronizing the core and jacket rotation and eliminating radial slippage.
2Reliability
If traditional soldering method is used to bond core to jacket, then radial slippage is prevented, but the method is not practical for solid metal cores
Solution Approach 1:
The traditional thermal bonding method (soldering) is replaced with a mechanical engagement system. The graduated thickness driving bands create a mechanical interlocking action with the rifling that prevents radial slippage without requiring thermal processes, making the solution applicable to solid metal cores that cannot be soldered.
Solution Approach 2:
The approach changes from controlling bond strength through temperature (soldering parameter) to controlling engagement characteristics through geometric parameters (driving band thickness). This parameter transformation enables radial slippage prevention through mechanical means rather than thermal bonding.
3Reliability
If copper-based jacket is used, then radial slippage is prevented through traditional bonding, but barrel erosion and fouling occur causing rapid accuracy degradation
Solution Approach 1:
The polymer jacket is designed as a consumable component that can be easily replaced. Rather than attempting to make the barrel durable against copper jacket wear, the solution accepts that the jacket will degrade and can be replaced, while the barrel remains intact and reusable. This reverses the traditional approach of protecting the expensive barrel from jacket wear.
Solution Approach 2:
The solution uses a composite construction with polymer jacket and metal core, where the polymer material inherently reduces barrel wear compared to traditional copper jackets, while the metal core provides the necessary structural integrity and ballistic performance.
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
The solution reduces costs, minimizes barrel wear, and maintains accuracy by preventing radial slippage, while being environmentally friendly by using alternative materials like tungsten or steel cores and reducing lead usage.
Implementation Method 1
The bullet core includes high-friction surfaces formed in a longitudinal direction or at a base of the bullet core. The modified surface increases friction between the bullet core and polymer, further decreasing radial slippage.
Implementation Method 2
When the project is fired, the pressure of the propellant swages the driving band into the rifling of the barrel to form a seal that prevents the gases from firing to blow past the project.
Implementation Method 3
The driving bands also engage the rifling of the barrel in order to spin-stabilize the project.
Data Source
AI summary
Provided is a polymer jacketed projectile with metal core. The projectile includes a metal bullet core and a monolithic polymer bullet jacket surrounding a portion of the bullet core. The jacket includes a series of radial driving bands cut into the jacket in a graduated configuration at increasing thicknesses. The graduation and increasing thickness of the driving bands allows gradual radial acceleration upon engraving of the rifling due to intentional radial deformation of the forward driving bands. Additionally, the bullet core) includes high-friction surfaces formed in a longitudinal direction or at a base of the bullet core. The modified surface increases friction between the bullet core and polymer, further decreasing radial slippage.