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

K. L. & B. J. Kosanke

ABSTRACT: A concussion mortar is a device used to produce jarring explosive sounds at events such as concerts and other theatrical productions. It consists of a heavy steel bar, drilled out to produce an explosion chamber. A type of pyrotechnic flash powder is loaded into the explosion 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 of concussion mortars, internal mortar pressure, recoil force and air blast were measured as functions of concussion powder load. It was determined that a full load (1 oz. 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 air blast 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, some of which have not been fully explained at the time of this writing.

Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 4, (1995-1997), pp 16-27

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