Current percussion primers in small caliber ammunition (i.e., 5.56 mm, 7.62 mm cal .50 and 20 mm) use a lead styphnate-based primer formulation that poses a long-term hazard to the environment and the operator of the weapon since airborne vaporized lead results from each successfully fired cartridge. Lead styphnate-based primer compositions are currently specified in all of the U.S. Army’s combat small caliber ammunition and in many cartridge actuated devices (CAD) and propellant actuated devices (PAD) used in U.S. Navy aircraft ejection systems, countermeasure applications, and stores release systems. The CAD/PAD devices are used by all Department of Defense (DoD) components and foreign militaries that utilize U.S. manufactured aircraft. Lead is a known toxic material, which pollutes test ranges and exposes the manufacturers and users of these devices to serious health hazard liabilities. Lead is regulated by the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA). Current EPA and OSHA regulations are directly impacting range and testing operations. Stricter regulations in the future will seriously impact or force closing of production, testing, and range operations. With the current production rate for all small caliber ammunition (less than 20 mm), the quantity of lead to be consumed for percussion primer production alone is well over 23,686 pounds or nearly 12 tons annually.
The purpose of this demonstration was to evaluate the performance of metastable intermolecular composite (MIC) primers with compositions formulated from commercially available lead-free nanoscale powders.
For these tests, the MIC composition was substituted for the lead styphnate-based primer composition currently used in conventional small caliber percussion primers. Small caliber percussion primers are used by the Army in small caliber ammunition and by the Navy in several CAD/PAD applications. In general terms, the MIC material is an engineered energetic composition consisting of a metal fuel (most often nanoscale aluminum) and metallic oxidizer that are exothermically reactive with each other. By utilizing nano-sized particles, the near nano-scale proximity of the reactants minimizes distances over which the fuel and oxidizer molecules must diffuse in order to reach each other, resulting in a dramatically increased reaction rate relative to that of conventionally sized pyrotechnic mixtures. Two of the most commonly used MIC compositions utilize molybdenum trioxide (MoO3 ) or bismuth trioxide (Bi2O3 ) oxidizers. These materials in a form of nano-sized particles offer the possibility of tunable energy release and high temperatures. One unique feature of MIC materials is their ability to produce particles hot enough to ignite a bed of propellant. Additionally, the MIC materials are impact sensitive, which makes them a good percussion primer mix candidate.
The demonstration tests conclusively showed that both small arms ammunition and several CAD/PAD devices employing a lead-free MIC primer composition met all performance specifications. MIC primer performance in M855 cartridges was found to be similar to that of the #41 lead styphnate-based primer with regard to bullet velocity and both case mouth and port pressures. However, single shot action time was found to be longer with both MIC primers tested. This result may be attributed to the low gas output of the MIC primers. Accordingly, rates of fire with both MIC primers were somewhat lower than that of the reference round. It is not immediately obvious why the water-based MIC composition, which has the lower single shot action time, has a lower rate of fire than the solvent-based MIC composition. However, both MIC lots met the 3.0 msec requirement. While tests demonstrate that action times for the MIC primers can be reduced with the addition of gas generating compounds (such as pentaerythritol tetranitrate [PETN]) to the primer composition, additional research will be required to determine if the goal of having a common composition for both Army and Navy applications can be reached.
The performance of the water-based MIC primer composition used in PVU-1/A hardware was found to either exceed or equal that of the standard lead styphnate-based PVU-1/A. This was true with regard to ignition delay and pressure rise time in lot acceptance test (LAT) closed bomb tests. Although the peak pressure data seems to suggest that the MIC primer performance was out of specification, the pressures with the standard PVU-1/A were also either high or low, indicating that the output charge weight had not been properly adjusted to meet LAT specifications when the cartridges were loaded. Use of the MIC composition will allow both the Army and Navy to eliminate a major source of lead contamination in manufacturing, logistical, and training operations with these devices.
In adopting the MIC primer technology for service use, a number of factors including, performance, toxicity, cost and availability of raw material, safety during manufacturing and loading processes, handling, and storage, and interface with existing and future loading processes need to be addressed by the Army and Navy qualification organizations. The successful demonstration of the Army MIC primer can now be used by the Program Manager for Maneuver Armament Systems (PM-MAS) to proceed with the authorization for an ammunition-based qualification test program that will lead to an engineering change proposal for qualifying the MIC primers. Once approval has been granted, a Mantech program sponsored by the PM-MAS would be required to proceed with the equipment prototyping and process alteration required to adopt the new MIC primer at Lake City Army Ammunition Plant (LCAAP).
Qualification of airborne CAD/PAD devices used by the Army, Navy, and Air Force is the responsibility of Naval Air Systems Command (NAVAIR) Program Office PMA 201 and the CAD/PAD Joint Program Office (JPO). For the CAD/PAD applications, the JPO is the authority for accepting the results of the demonstration plan for the Army and Air Force CADs and PADS deployed on board U.S. Army and U.S. Air Force aircraft. NAVAIR PMA201 is the authority for accepting the new primers into the Navy inventory and for foreign military sales.