A
swarm of
shot from a
shotgun or similar emitter of multiple lead pellets. The shot pattern usually follows
Gauss'
normal distribution.
In the
US, the
quality of a shotgun/shot combination is often measured as the
percentage of the shot from a shotgun fired from a distance of 40 yards that can be included in a circle with a diameter of 30 inches.
To get an idea of irregularities in the pattern, the number of 5 inch diameter circles not hit by a single shot within the 30" circle is counted. A larger number indicates a more irregular pattern, perhaps due to shot of low quality or a damaged or worn barrel.