At the range I was in charge of we required people to stand back at least 45 feet from the patterning board, and use nothing larger that 7 1/2 shot.
Why?
Because that was the least amount of distance required to avoid damage to the patterning board. The spread and loss of velocity of the shot at that distance.
The discussion here is generally about home defense, i.e. within your own home. Distances of 7-12 feet.
If the interior of your house has distances of 30’ to engage intruders, then you can probably afford to arm yourself with M16, 100 round drum and an M203 slung underneath...
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