Impact Resistance of Plastic Shotgun Shell Wadding

Having been practiced competitively for centuries, the tense and demanding sport of shooting is once again gaining popularity round the world. Competitive shooting events fall into three disciplines: Rifle, Pistol, and Shotgun events. In Rifle and Pistol events, competitors aim at a 10-ring target from a set distance (10m, 25m or 50m). Depending on the event, athletes are required to shoot from standing, kneeling or prone (lying down) positions. In Shotgun events, competitors shoot at moving clay targets launched above and in front of them. Skeet shooting is one of the three major types of competitive shotgun target shooting sports -the others are sporting clays and trap.
Participants in skeet, trap and sporting clays attempt to break clay disks that have been flung into the air at high speeds and/or from a variety of angles. The firearm of choice for this task is a shotgun. Unlike rifles which fire bullets, shotguns fire shells which are self-contained cartridges loaded with shot (pellets) specifically designed to be fired from a shotgun. Within the shell is a plastic cup called “wadding” that holds the pellets. With the ignition of the gunpowder by the primer the wadding and pellets are driven out of the barrel. As the lighter plastic wadding exits the barrel, hitting the open air the wadding slows down and the pellets are carried along their course by inertia. A properly designed/manufactured wad forms a critical gas seal at firing to keep the expanding gases behind the shot charge. Wads also act as spacers, setting the correct volume for the propellant and shot charges and cushioning the pellets to reduce deformation. Faulty wads can cause the pellets to jam tightly in the barrel, such that they do not exit the shotgun in the anticipated pattern, or velocity – thereby causing the shot to be missed.

We were approached by a supplier of shotgun shells to perform instrumented impact tests on some of their plastic wads. When assembled the finished products made from the control lot of material performed as expected. However shells made from the sample lot of material failed on a consistent basis. For this testing we used an Instron 9450 with High Energy Option; instrumented tup, DAS (data acquisition system) and Bluehill Impact software. A custom fixture that would support the plastic wad as closely as possible to its finished application was constructed. The fixture had a small through hole in the bottom to allow the tup insert to pass completely through the wad. A custom tup insert was made to simulate the primer charge. The High Energy Option was used so that the crosshead could be fired at a high velocity in hopes of simulating the amount of force that the bottom of the wad would see in its final use.