In-Chamber Primer Force and Case Pressure Measurements of the 5.56-mm Cartridge

Report No. ARL-TR-5862
Authors: John J. Ritter, Richard A. Beyer, and Anthony Canami
Date/Pages: January 2012; 38 pages
Abstract: A custom, in-house designed breech for an M16A1 Mann barrel, 5.56 mm, has been instrumented to measure the force output of an unsupported primer. In addition, the Mann barrel was designed to accept gauges at two diametrically opposed locations to simultaneously measure mid-case chamber pressure. This unique apparatus provides an advanced diagnostic tool to obtain insight into the interactions between the primer and propellant bed of the 5.56-mm cartridge during ignition, and allow for better characterization and understanding of the cartridge's interior ballistics. Experiments were performed to investigate the role of the primer, temperature conditioning, and charge weights to determine their respective effects on chamber pressures and primer forces. This systems level approach provides detail into the primer-propellant interactions never before observed. Experimental results indicate the primer force measurement is an invaluable tool in evaluating the interior ballistics of the 5.56-mm cartridge, and provides early time information that pressure measurements alone overlook. Whereas standard mid-case or case mouth pressure measurement diagnostics begin when the propellant gas generation is first observed, this novel diagnostic approach shifts the initial data acquisition timeframe back to when the firing pin strikes the primer.
Distribution: Approved for public release
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Last Update / Reviewed: January 1, 2012