Experimental Studies of the No. 41 Primer and Ignition of 5.56-mm Ammunition

Report No. ARL-TR-3922
Authors: Anthony W. Williams; Andrew L. Brant; Pamela J. Kaste; Joseph W. Colburn
Date/Pages: September 2006; 46 pages
Abstract: Understanding the underlying physics of the ballistic event is important to gun system design and in determining corrective measures necessary to address unexpected results (misfires, variations in muzzle velocity, projectiles stuck in-bore, etc.). The present study characterizes the output of the small-caliber primer (no. 41) in open-air and ballistic simulator experiments and full-scale gun firings. Through the analysis of high-speed digital photography data, pressure-time data and particles recovered from the primer, the small-caliber primer and ignition system have been characterized. The open-air experiments reveal the primer particle size, velocity, and composition. These data are used in a separate and parallel effort to develop a detailed primer model in which both gas and particle features are captured. A series of tests were also conducted using a ballistic simulator fixture. The fixture incorporates an acrylic chamber that simulates the 5.56-mm ammunition geometry. The primer output is characterized by measuring the pressure-time response within the simulator chamber. High-speed videos of flamespreading due to the primer indicate that the flame front penetrates no more than 40% of the propellant bed. In addition, there is evidence that the propellant bed is compressed in the region near the base of the projectile. Gun firings were conducted in which pressures were measured inside the chamber and at the case mouth. In-bore radar data were collected and correlated with the pressuretime response measured in the chamber. From these data, it was determined that the projectile begins to move into the gun tube at a pressure between 20 and 30 MPa. Case mouth pressures and projectile velocities were within the specifications for the M855 small-caliber round. The experimental work discussed herein is being used to validate a detailed small-caliber primer model and an ARL-NGEN CFD model.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2006