Ernest Hemingway wrote in, I think, The Green Hills of Africa, words to the effect that the rifleman practices long-range surgery. He knows the animal’s anatomy and knows exactly what effect the bullet will have on the target before he sends it on its way.
Shotgun shooting doesn’t work that way. The random nature of pellet distribution means every pattern is different, and each one strikes the target with different numbers of pellets in different places. A shotgun pattern is less like a surgeon’s scalpel, and more like a miniature volley fired by tiny Revolutionary War-era redcoats at a bird: the cumulative effect is deadly, but you never know where the individual shots will land or how many will hit the target.
Obviously pellets in neck. vertebrae or the brain kill immediately. That much I know for sure. After that, my understanding of what goes on when the pellet meets the bird gets murkier. Is it shock or is it pellets penetrating vital organs that kills birds? You see examples of both in the field.
In some cases, mostly with smaller birds, pellets do go all the way through, into vital organs and often out the other side. I rarely encounter pellets in ducks and doves when I clean them or when I eat them. I shoot steel 7s at doves and 2s almost exclusively at ducks.
Geese are another case altogether. They are big birds with lots of breast muscle, and I often find pellets (I like either steel BBs or my dwindling supply of tungsten-iron Bs and 2s) lodged in the breast meat when I am cleaning geese. And yet, those pellets that don’t adequately penetrate to the vitals still kill birds. The day I lost my rangefinder I also shot a limit of three geese. One fell completely dead. When I dressed it I found three pellet holes in it, all in the breast. One had penetrated only about half an inch (it was a tungsten-iron Winchester Xtended Range 2 and I shot the bird at 20 yards or so). I didn’t find the other two, but I didn’t find holes in the heart or a body cavity full of blood, either.
The second bird, shot at about the same distance (I doubled), had half a dozen holes in the breast and folded and fell seemingly stone dead, only to revive sometime later. The third goose I shot that day was hit by exactly only pellet in the lungs, but it fell immediately incapacitated. From evidence like that, it seems like shock does knock birds from the sky.
But, I’ve also seen geese hit hard that kept flying, only to pile up hundreds of yards away with several holes in them. Go figure.
Then there are pheasants, which are just plain tough. It doesn’t help that we shoot most of them going away, so the vitals are shielded. On the last day of the season I hit a going-away bird hard with a load of lead 5s and later found about 10 holes in the back end—which was all I had to shoot at. It rocked, righted itself, and would have flown over a hill had it not made the error of flying past Springerman3, who shot it in the head. Now, if one of my pellets had broken a wing on that bird, I’d have either found it dead where it dropped, or the dogs would have picked it up a few feet from the spot. As it was, without Springerman3’s assist, we would have had a very hard time finding that bird.
Through a combination of decent shooting, pretty good shot selection, determination to find what I shoot, and luck I don’t lose many birds. Still, I go back and forth on shot size. Sometimes I think smaller must be better, other times I think big pellets are the ticket. More, smaller pellets increase your chances of a head and neck hit, or of putting several pellets in the body and breaking a wing. Fewer, bigger pellets penetrate deeper into vital areas. All I do know for sure is that shotgunning isn’t surgery, but it works.