To comply with perchlorate regulation, the military services aim to replace pyrotechnic ingredients based on perchlorates and heavy metals in small arms ammunition. This demonstration project focused on replacing IM-28, an incendiary mixture that is nose-fitted in the US Army and Navy’s M8, M20, and Mk257 armor-piercing incendiary (API) rounds, with a suitable perchlorate-free and barium-free composition. IM-28 contains potassium perchlorate and barium nitrate and annual production exposes personnel and the environment to tons of these ingredients. Replacement of IM-28 has hereby been demonstrated feasible as part of a three-way teaming between the Combat Capabilities Development Command - Armaments Center (CCDC AC, team lead), the Naval Surface Warfare Center (NSWC), and the Lake City Army Ammunition Plant (LCAAP) contractor, currently Northrop Grumman Innovation Systems (NGIS). This demonstration was accomplished by fabricating bullet lots derived from the replacement composition and then gunfire testing the lots with existing production and quality control methods at the prime small caliber ammunition manufacturer LCAAP, a government-owned, company-operated (GOCO) facility. The government laboratories (CCDC AC and NSWC) collaborated on formulation development, while the contractor operating LCAAP fabricated and demonstrated the candidate compositions in the full-up M8, M20, and Mk257 APIs.
Many small arms ammunition combine perchlorate oxidizers with a metal reducing agent (fuel) to achieve an incandescent flash useful for igniting volatile chemicals present in fuel tanks. Because of the regulatory drivers associated with perchlorate oxidizers, tremendous pressure is placed on the Department of Defense (DoD) to implement perchlorate-free technology. Its technology solution to the perchlorate problem is to remove the potassium perchlorate from IM-28 and substitute alternate oxidizers such as metal nitrates. Additional fuels, processing aids, or unconventional oxidizers were evaluated during downselection to enhance the incendiary effect and storage stability if needed. A similar approach based on sodium nitrate has been proven out as a potential solution in the Strategic Environmental Research and Development Program (SERDP) project WP-1424. The primary concern with this approach, however, lies in the hygroscopicity of sodium nitrate. This oxidizer absorbs ambient moisture very readily even if used in conjunction with a processing aid, which could impact the long-term system reliability and performance. In addition, concerns had been raised by the operator of LCAAP (NGIS) regarding the manufacturability of the sodium nitrate technology in the humid summer weather at the manufacturer site (Independence, MO).
The new technology consists of a replacement nose-fitted incendiary composition based on sodium metaperiodate (SMP), magnesium-aluminum alloy, and calcium stearate. These are commercially available ingredients that do not contain perchlorate or heavy metals or pose any additional Environmental Safety and Occupational Health (ESOH) risks. Upon penetration of an armored target, this composition is compressed by the nose of the deforming copper alloy jacket and the penetrating stainless steel core. This triggers the combustion of the composition to produce the necessary “flash” so useful for igniting fuel vapors in armored vehicles and storage containers and to aid adjustment of fire by marking the impact point.
The program concluded with a successful demonstration of the perchlorate-free and barium- free incendiary composition in three .50 caliber bullet platforms: the M8, M20, and Mk257 APIs. The new composition does not contain heavy metals, perchlorates, or any other currently regulated materials. It can be produced at the prime small caliber manufacturer, LCAAP, using the existing production setup currently in service for regular .50 caliber production.
Despite the technical success of this program, the report stated that there are a few items to address before the new composition is ready for implementation by relevant Program Managers. First and foremost, the new composition needs to be further qualified by safety and stability testing by the Army and Navy. This was originally part of the program scope but was traded for additional system level testing at LCAAP in the last phase of the project. In addition to the safety testing, a military specification document (MIL-SPEC) needs to be written for SMP and approved by all military services to ensure quality control for SMP and any items derived from the new composition. Lastly, additional system level testing leading to final hazard classification (FHC) will be needed for technology transfer to the appropriate system owner(s). Such testing would likely include fabrication and ballistic testing of larger lot sizes to be more representative of regular production lots.