That one inch per yard thing is not accurate at all. It depends on a lot of factors. What kind of shot you're using and how you are choked. I have shot pattern boards before and I can tell you that was a long distance shot. When I shot the piece of fire wood the other day from about 10 yards or so all of the pellets hit within about an inch of each other and I have no choke at all. Cylinder bore.

So I've done a little more studying and I think we're both a little off. It looks to me like that spread is about 50 ft based on some videos I saw with birdshot. Buckshot would make him much tighter group. My idea of using birdshot was for fighting inside the house and my logic is that I will not over penetrate walls but anything inside the house number 9 birdshot should be lethal.