Comparative Evaluation of 20mm Developmental Ammunition - Interior Ballistics Test.

The Interior Ballistics Laboratory evaluated the interior ballistic characteristics of four experimental round as part of an overall performance evaluation of improved 20mm ammunition. The rounds were Armor Piercing Incendiary API, Semi-Armor Piercing Incendiary SAPI, and Semi-Armor Piercing High Explosive SAPHE developed by the Air Force and the General Purpose Armor Piercing High Explosive GP APHE developed by the Navy. Standard M56A3 rounds were also fired as control rounds for comparison. Chamber pressure versus time and action were measured with the ammunition and gun conditioned and fired at temperatures of 155, 75, and -60 degrees Fahrenheit. Muzzle velocities, muzzle eergies, and integrals of pressure were calculated. The interior mballistic characteristics were within acceptable limits except for SAPI which had low muzzle energy at 155 degrees and the GP APHE which had excessive peak pressures at all three temperatures. Author