UNCLASSIFIED
Distribution A. Approved for public release: distribution unlimited
UNCLASSIFIED
The ARDEC Gap Test for Small Grain Gun Propellants
Mr. Erik Wrobel*
Detonation Physics and Experimental Technologies Branch
Mr. Lucas R. Lopez
Propulsion Engineering Programs Branch
Mr. Chau Nguyen
Mr. Matthew Adelman
Munitions Safety and Hazard Classification Branch
U.S. Army Research, Development and Engineering Command
Picatinny Arsenal, NJ 07806
Keywords: Interim Hazard Classification, IHC, Shock Sensitivity, Gun Propellant, Gap Test
Abstract
The United Nations (UN) gap test, Test 2(a) has undergone numerous revisions over the last several years. Historically, Test
2(a) was conducted at the U.S. Army Armament Research, Development, and Engineering Center (ARDEC) to evaluate the
shock sensitivity of energetic substances for the purpose of hazard classification. Originally envisaged as a one-size-fits-all
energetic material characterization test, it presently does not adequately differentiate the hazards of propellants, pyrotechnics,
and high explosives. The 2012 revisions to the TB 700-2 gap test procedures aimed to simplify the experimental setup but
resulted in vague pass/fail criterion, complicating the local Interim Hazard Classification (IHC) assignment process.
Modifications were made to this standard test to improve the quality and relevancy of the data collected while utilizing the
same high explosive booster and sample tube.
The resulting ARDEC Gap Test measures the detonation velocity in an energetic substance as well as the dent depth produced
in aluminum. The detonation velocity and dent depth metrics conclusively determine whether or not a sample material
propagated a detonation in the UN gap test configuration. New assessment criteria were written for the test, allowing a better
evaluation of the shock sensitivity hazard of a sample material. The ARDEC Gap Test has been conducted on numerous small-
grain propellants, M9 flake propellant, and two high explosives. ARDEC is currently utilizing this test to support IHC
assignment for small-grain propellant formulations.
