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There is an abundance of experimental data on the ballistic performance of sporting shotguns. However the successful development of computational models, that will help to reduce the commercial and environmental costs of extensive test programs, has been elusive. This paper describes the development and evaluation of a 3-D model that uses a commercial implementation of the distinct element method. The simulation gives realistic results for the effect of muzzle chokes on the spread of shot and provides evidence to support the well-known belief of practical shooters that a tapered constriction of 0.040" (1.02 mm) in barrel diameter, the so-called`full-choke', produces the optimum shot pattern. Detailed investigation of the internal ballistics of the shotgun shows that the reduction in diameter at the choke serves to compress the shot laterally as it exits the gun barrel. This affects the severity of interparticle collisions, creating a tighter, more uniform pattern. The accuracy of the computational results in the absence of air resistance tends to imply that the internal ballistics, rather than aerodynamic drag, dominates the shot pattern, although not the penetration power, over short ranges. Useful predictions of shotgun performance might then be obtained without resorting to full computational¯uid dynamics simulation or to extensive ®eld trials.Units: Obsolescent British`Imperial' units such as inches (") and ounces (oz.) and pounds (lb.) are still in widespread use for some of the critical dimensions and weights relating to ®rearms and ammunition, especially in legal de®nitions and in everyday speech. These units are retained in the text when appropriate. Equivalent ISO units are given.

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cal the ble A major purpose ot the I echnl-Information Center is to provide broadest dissemination possiof information contained in DOE'S Research and Development Reports to business, industry, the academic community, and federal, state and local governments. Although a small portion of this report is not reproducible, it is being the availability of information on the research discussed herein.

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