U.S. Army seeks environmentally friendlier ammunition

The U.S. Army uses a lot of bullets and explosives to fight and win on the modern battlefield. Known chemical compounds that explode, technically known as energetics, are lead-based primary explosives. In new experiments, Army researchers and their partners at Purdue University observed some new compounds that may be an environmentally friendly alternative.
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A soldier fires an M4A1 assault rifle at Joint Base Lewis-McChord, Wash., Jan. 13, 2020 (Picture source: U.S. DoD)

In a peer-reviewed paper published by Chemistry – A European Journal, researchers from the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory and Purdue University describe the synthesis of new environmentally friendly primary explosive materials. These green replacements could find applications in small, medium and large-caliber bullet and gun propellant ammunition.

What makes this research ground-breaking is that two unique backbones, known as heterocycles, that form the basis of energetic materials, were combined in a way never achieved before. Researchers said the result is a very high energy, high-nitrogen content with a high gas generating ability, all desirable attributes for an explosive.

The Army has been searching for solutions for many years to develop lead-free primary explosives that satisfy environmental regulations associated with lead contamination. This research supports the Army’s modernization goals of Long-Range Precision Fires and Soldier Lethality. Researchers said percussion primer mixtures, which contain primary explosives, are typically found in just about every bullet that can be imagined that is shot from a gun or tank.

Prof. Davin Piercey, assistant professor of Materials Engineering and Mechanical Engineering at Purdue University, and his group did the lion’s share of the work with the synthesis efforts for these materials, according to Army researcher Dr. Jesse Sabatini. “The development of these materials provides a potential pathway for toward the development of lead-free technology,” Sabatini said. “We were just happy to have played a role in assisting his efforts here so that the molecules that were pursued were the right ones.”

The Army’s corporate research laboratory and Purdue worked jointly to develop the synthesized targets on paper, but Purdue synthesized these materials in their lab, Sabatini said. The Army provided the historical context of primer development.

Explosives are used not just for blowing stuff up. Inside of a bullet casing, there is a small amount of primary explosive which is used to ignite the powder inside the cartridge. One of the materials that are used in there right now is lead styphnate. “Right now, whenever you are shooting, you’re going to be spreading lead into the air around you,” Piercey said. “Any use of lead is going to end up polluting the environment in small amounts. The more lead that you remove, the better it is for the environment.”
Piercey pointed to a study that found that people who had been shooting a lot had elevated lead levels.

The joint effort between the Army and Purdue highlights the laboratory’s Open Campus business model, which allows for collaboration between Army researchers, academia, industry and small business, both nationally and globally.

Sabatini said he hopes to see this research result in real-world solutions for American Soldiers. “If you aren't making stuff that transitions, that leaves the lab and goes to formulators, then you should not even be in this business,” Sabatini said. “This joint research has the potential to be transitioned to our Army partners that work in primary explosives.” Piercey pointed to a video his team made showing silver salt detonating when heated. He said the video shows the high performance of even small amounts of the new primary explosive. Sabatini said he envisions future work with Professor Piercey's team as they jointly develop ideas that we are interested in for the benefit of the Department of Defense.

This research has the potential to be transitioned to Army partners that work in primary explosives. Sabatini said there is interest from the CCDC-Armaments Center at Picatinny Arsenal, New Jersey, to explore these compounds for primary explosive-based applications for bullets and gun propellants. The next step is to find a transition partner.

A provisional patent has been filed for this technology (track code 2020-PIER-69143) through the Purdue Research Foundation Office of Technology Commercialization. Read more at the Purdue University News Room.

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