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I recently designed a low-velocity shotgun slug for a smooth-bore barrel. This single-piece bullet is nonlethal, and designed for very short ranges and low, subsonic speeds. It is also inexpensive to produce.
Simple design leads to affordable manufacturing
The projectile is fin-stabilized and works in any slide-action shotgun.
I started with hand sketches, then created a 3D CAD model. Next, I ran a computer simulation using a CFD program to test stability.
After research and several iterations, a stable design emerged. They made it via 3D printing. Assembling shotgun shells followed, leading to test-firing.
It Paid Off
To my surprise, all test bullets clustered into a two-inch group from 50 feet.
My experience managing over 20 wind tunnel tests provided significant help. I also reviewed over 200 wind tunnel reports over the years.
Wind Tunnel Testing is Costly
Wind tunnel testing requires a lot of electricity. To manage this, we schedule runs for the evening and early morning hours. This helps reduce the load on local power plants and lowers costs.
Models and Electronics Hand-Built
Building wind tunnel models is very expensive. Before 3D printing, engineers made models by machining aluminum or steel blocks. Models include nearly 100 pressure ports to record various pressures.
An electronic force balance captures forces and torques generated by the model. All of this is hand-made.
Usually Not Nearby
Wind tunnels aren’t usually easy to access. Testing crews must pack everything and fly there. They rent cars and book hotel rooms. They work from 7:00 P.M. to 9:00 A.M. Testing needs at least two crews, each with two people. Often, they require more.
We can’t access the CFD code. So, we will need to do manual pre-test analysis and run several test iterations. They would follow this with retesting until they find a workable configuration.
Norman T. Neher, P.E.
Analytical Engineering Services, Inc.
Elko New Market, MN
www.aesmn.org