Stop!! Mr Holmes is calculating the shot distance

The shotgun is generally meant to cover a wider area with shots & thus kills birds & other animals, that are rather difficult to aim with nonrifled fire arms like shotgun. Here , due to non rifling the bullet aim is not very precise.

*Rifling gives a spin to the bullet & gives stability like a spinning top, so the aiming is very correct.

Although the shot gun is not meant for human beings, unfortunately its criminal use on humans is very common. A SBBL means single barrel gun & DBBL means double barrel gun. The bullet used in shotgun contains many small pellets that disperses after firing and covers a wide area for damage. Some dispersion is controlled by providing a narrow constriction at the end of muzzle, known as "Choking".
The pellet disperses soon after the exit from muzzle & the degree of dispersion increses with the distance.
One can calculate the distance from which fire was shot by seeing the pattern of pellet impact on the hit surface, either the victim's body or other things.
Other things also account for the pattern , like when the fire is shot at contact , there is burning & tattoo formation & the wound is torn like a rag.
When the fire is done from a few inches, hole is formed there is burning , blackening & tattooing.When the distance is 1 yard there is singeing & blackening,,,,so on.

* see the picture for detail*.

So now you can actually imagine the scene of firing, by calculating the distance.