Concussion Mortar Internal Pressure, Recoil and Overpressure as Functions of Powder Mass

Kenneth L. and Bonnie J. Kosanke

ABSTRACT: A concussion mortar can be defined as a device used to produce a noise and jarring shock for dramatic effect at events such as stage productions. It consists of a thick-walled tube, closed at one end to form a combustion chamber (barrel). A type of pyrotechnic flash powder is loaded into the combustion chamber and fired with an electric match. Although concussion mortars are used quite frequently, for the most part, detailed measurements of their manner of functioning have not been reported in the literature. In the present study, internal mortar pressure, recoil force and overpressure (air blast) were measured as functions of concussion powder load. It was determined that a full load (1.0 ounce or 28 g) of a strontium nitrate and magnesium concussion powder produced peak internal pressures averaging approximately 3100 psi (21 MPa). It was also observed that the width of the pressure peak ranged from approximately 7 ms for light loads, down to less than 2 ms for heavy loads. The recoil produced for a full load averaged approximately 5.9 lbf·s (26 N·s). The peak overpressure for a full load, at a point 5 feet from and 3 feet above the mortar (1.52 m and 0.91 m, respectively), averaged approximately 1.5 psi (10 kPa). In addition, there were a number of unexpected observations, which have not been fully explained at the time of this writing.

Keywords: concussion mortar, overpressure, recoil force, internal pressure, flash powder

Ref: JPyro, Issue 1, 1995, pp 26-36

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