It took months of work, thousands of pounds of steel, and more than a dozen welders and mechanics to turn engineer Diep Ho's vision of a steel bunker that would provide shock-proof protection after a propelled charge was detonated into a reality.

The Ballistic Simulator (BSIM) Bunker is a non-permanent structure of steel reinforced with concrete blocks that surrounds a ballistic simulator. The Yuma Test Center (YTC) machine shop team recently built the bunker for the first time at YTC.

Daniel MacLeod, Ammunition and Ordnance Testing Officer, explains what goes on inside the Ordnance Factory and provides key information to customers.

“What the customer gets is a detailed visual representation of what's going on inside the simulated chamber.”

The ballistic simulator is fitted with a clear acrylic tube that resembles a weapons system's chamber, and when fired, a high-speed camera captures 30,000 frames per second.

“We film the first 7 to 10,000 psi to see what's happening before the explosion occurs,” McCloud explains, adding, “What they're looking at is the very short window of time between when the detonator ignites and when that energy is transferred to the charge inside. The only way they can capture that is with high-speed video.”

Ho, a munitions and weapons tester known for his ingenious inventions, designed the bunker to film video in a safe, controlled environment, with peepholes for high-speed cameras, wiring for data-gathering equipment, deflection panels to withstand the pressure of munitions and contain the remains of acrylic tubing that shatters with each shot, lighting, and ventilation.
“We had to design a bunker that could contain all the burnt propellant and broken acrylic,” Ho said.

He enlisted the help of a highly skilled and trusted machine shop team that regularly manufactures explosion-proof structures, bunkers, blast shields and catch boxes. They used armored steel plates that can withstand impacts. If all the plates were laid out side by side, they would be a mile long, Ho said.

Fernando Godinez, the lead welder on the project, said the most challenging parts were the doors and hinges, which he fashioned out of steel. “Everything had to be balanced,” he said. He estimates each door weighs about 600 pounds.

Mr Ho explained: “It had to be made so that it could open and close – it could get pushed out by internal pressure – so we had to think about how to hold it all together.”

The team fabricated the parts in a welding shop and transported them to the test site for assembly. With the help of support services personnel, they put the remains of the unusable concrete target panels into place and installed the steel bunkers on top of them.

“The floor is in two pieces, the walls are in another piece, the roof is in three pieces, and the frame is all separate,” Godinez explained.
Ho also designed the table on which the ballistic simulator rests, and Pablo Villalobos, who helped source all the materials, estimates that the table alone weighs 10,000 pounds.

The bunkers are left unpainted, giving them a rustic, industrial look, because the heat of firing would melt the paint and produce toxic fumes.
Another unique aspect of this non-permanent structure is that it was constructed with recycled steel procured from a federal agency through recycling services, which reduced the cost of the project. Ho secured an inventory of available materials and used only those materials to fabricate the bunker.

“We looked for materials first, then designed the bunker based on what we had on hand,” meaning the materials were not uniform. “We had to do a lot of machining — cutting this, cutting that — and that was hard work. We built it with what we had on hand.”

After the machine shop and welding departments had been working separately for several months, the teams were brought together at the test site to review the work.

“The fabricators, the welders, everybody here pitched in,” Villalobos said.

Greg Branch and Matthew Keddy, who worked with Ho for months on building the table and making many improvements to the safety latch, said they were “glad it's finished, glad it works” and “it turned out really well,” respectively.

The first BSIM test was conducted successfully in March 2024 and the client, PM-CAS, was pleased with the data collection and test results. A post-mortem review commented that the new BSIM site was professionally constructed and would be a valuable subscale tool.