APPENDIX I: RESISTANCE TO PENETRATION

The significant resistance that feathers and skin provide against penetration by pellets was recognised by Lowry, who suggested that an impacting pellet required a kinetic energy of at least 0.4ftlb to perforate. This related to pellets sizes in the region of No.4 to No.6 which, at most, equates to an energy density (i.e. energy per square millimetre of presented area) of 0.1 J/mm². Lowry's figure was largely based on qualitative observation … to achieve a valid estimate of shotgun effectiveness against game requires specific measurement, so a test was conducted using the breast feathers and skin taken from a harvested mallard. It is not known whether the presence of other tissues supporting the interior face of the skin significantly affects the penetration resistance of the skin, so the skin was placed in contact with a block of 20% ballistic gelatine. Half of the gelatine block was left exposed, and then the entire gelatine block was fired at using No.6 lead shot from a full-choked gun at 30m range. Six shots were fired to produce a sufficient number of hits. The measured penetration of shot into the exposed gelatine was then used to calibrate the gelatine strength which in turn was used, together with penetration behind the skin, to determine the residual velocity of the pellets after perforating the skin.

Enhanced image showing shot penetration into a gelatine block, with and without overlying feathers and skin.

The penetration resistance model used is

where

The perforation energy density is given by

The observed perforation energy densities were in the region of 0.2 J/mm².