I only know of two failures to stop and luckily they were both officers. One took birdshot (not sure what) to the vest, sholder and face at about 30-40 ft. Another took birdshot to the face at long range. The first officer is still undergoing surgery almost a year later for nerve damage though.
The bright side is the large number of success's we've had w/the shotgun to stop.
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Vern