Optimized Riflescope Mount

The goal of this project is to create a lightweight riflescope mount (Ultramount) that is comparable in strength and production cost to an existing model made by Nightforce. To do this, a two component method is being pursued. First, a force simulation acting on the mount backed up by live fire data and a comprehensive math model, will be used to pinpoint high stress regions within the Ultramount, and optimize the geometry for weight reduction purposes. This simulation will be used to create several designs, which will be 3D printed, and validated using displacement test methods. Second, an investigation into better materials for Ultramount fabrication is being conducted to compliment the new design. Combining aspects between mechanical design and simulation, along with optimal material selection, an ideal riflescope mount may be fabricated.

=Problem Definition=

Background
Nightforce desires an in-depth analysis of the economic and material optimality of their Ultramount riflescope. They requested the development of a lightweight model that would meet or exceed current Ultramount specifications, in addition to maintaining current production costs. The client specified their current model’s alloy used for production, in addition to strength, spatial, mass, and durability requirements at the first team/client meeting. Military-specifications, previous live-fire testing, etc. were also discussed. Required files were given to the team to begin work on the simulation of the mount.

Deliverables
•	Create a force testing math model, that would accurately summarize the rapid impulse effects on the dynamic forces acting on the mount.

•      Present a proof of the aforementioned math model in the form of a proof of concept, in which a simple geometry will have a rapid force applied to it

•	Implement math model into mount design, and use for geometric optimization. Ideally, this will be used for not only the Ultramount, but for other products in the future

•      Deliver a comprehensive material study taking into account specifications (listed below) along with a recommendation on which material to pursue

•	Deliver final 3D printed prototypes with improved design and reduced weight and material cost

•      Provide design details, procedure, and conclusions in a concise research document for review by sponsors and the University of Idaho

Specifications
The new prototype mount was qualified upon the following specs, followed by how we plan to meet the specification

•	Corrosion resistance in saltwater environments

♦      Material design will be limited by a materials corrosion rate. For a material to qualify, it must be able to have a hard-anodizing coat to the same standards (MIL-A 8625) as the current Ultramount

•	Capable of surviving within a temperature range between –40 – 225 °F

♦      Disqualify any low melting point materials such as low-end polymer.

•	Capable of surviving recoil of 10,000 rounds on a corresponding rifle

♦      No simulated stress will be allowed within a close range (~35 ksi) of yield stress for a given material. Design and material selection will be kept to such a standard as to meet or improve upon Ultramount capabilities

•	Must look visually appealing

♦      Qualified by sponsor approval and subjective recommendations, if our customer finds it to match their current design profile, then visual appeal is considered confirmed

•	Will maintain position after a standard 5-foot drop test.

♦      New prototypes will be mounted to the rail and dropped 5 feet. If position and adjustments remain unshifted, then our design is validated

•	Must be lighter than 3.689 ounces

♦      Through implementation of known densities of materials, the final design aim will be 50% weight reduction, but validation will be anything less than the Ultramount's current mass

•	Cost effective compared to current model

♦     Material and production cost will be scrutinized thoroughly throughout the design process, and final dollar values for production of mounts using selected materials will be provided for comparison by Nightforce

=Design Considerations=

Material Selection
A materials candidacy study was conducted based upon the above specs. Metal alloys, polymers, and composites were all considered. Polymers, while lightweight and strong in some cases, would fail in terms of cost effectivity and optimal temperature range. This eliminated all but carbon fiber reinforced polymers. Other composites considered were glass fiber reinforced polymers. Over 50 Al-alloys were examined for comparable properties, but only a handful possessed the strength and low density to continue in the selection process. Magnesium and Titanium alloys were also considered. After checking the corrosion resistance, and temperature range, each material was indexed according to its Young’s modulus (E), yield strength, cost per unit volume, and density. The results and most attractive candidates based upon the indexes were shared with the client and team, allowing for further steps to be taken in acquiring quotes for the various materials and taking note of the bulk price for each material.

Over the course of the winter, over 15 companies were quoted for material prices, which provide the range of values given below.

The large range for magnesium alloys is due to national and international trade. Lower prices can be obtained internationally for AZ61A, but due to increased border cautions due to spreading illness, it was not purchased. All pricing given above has shipping,handling, and import cost accounted for.

Finally, a validation study for corrosion and hard coating of materials was performed. Al-7068 would hard coat quite similarly to that of 7075, 2024 would have issues hard coating due to its high copper content (3-4 wt%), and Mg-AZ61A has hard coating capability, but would result in a thinner coat overall, and would be less effective. Salt spray testing to MIL-A 8625 specifications would need to be performed on hard coated Mg-alloy prototypes in order to validate this for future use. Hard coating any of these alloys in bulk (4000+ parts) would fall in the ball park of $500/batch.

Data Analysis and Prototype Development
After 80 live fire recordings, accumulating 1.6-1.92 million points of acceleration and force data on the front and rear of the rifle scope mount and rail, peak forces were taken from each shot, and applied into modeling software to predict where high stress regions may occur in the mount. Based on this, a worst possible scenario simulation was ran, enacting the highest stresses upon the mount. From there, mount geometry could be optimized.

Below is the finite element analysis used to apply force in the simulated scope (assuming clamping points as fixed positions).

The following prototypes were developed via different approaches. They are shown in the table below. =Project Learning=

Proof of Concept
In order to prove our assumption of a simple F=m*a relationship enacting on the mount, a proof of concept (PoC) was needed to be designed. This took several iterations, all trying to show that a short, sharp force enacting on a simple geometry would be able to relate a math model to the mount as a whole. Originally, a stool and a hammer were attached and dropped from a set height to get repeatability in results, but to get a more accurate angular velocity, and striking angle in general, a secondary box PoC was developed. Both of which are shown below.

Simulation Stress Outputs
While acquiring a realistic math model, simulation with the understanding currently known by the team was performed, changing independent parameters, with the intent of getting realistic peak strain values in the mount (≤ yield strength of the material). Despite manipulating force application regions, material properties, =Final Design=

=Validation= Research is validated through in depth literature research given in the references below, and the prototype is validated via a standard 5-foot drop test, in which it must survive without flaw. =Team Members=

=Additional Documentation=

Project Schedule



Meeting Minutes































Presentations



Client Interview