I well remember my first grouse. He flew parallel with a logging road that about four of us kids were walking up to, out of a woods, doing a drive, as we were pretty much clueless about how to hunt grouse. Every single one of us was equipped with a single shot, mine was the only hammerless version. The three other guys fired and missed, and as the grouse flew past me, I fired, and he tumbled from the sky, hitting the ground right in front of me, where he flopped until I pounced on him. I was fourteen years old, and king of my tribe for the rest of the day.
Upon examination of the grouse, I discovered he had the wad from my shell stuck in his armpit. If a single BB had touched that bird, I found no evidence of it. I had simply knocked him off balance, and, if he had a moment or two more to flop, I expect he would have shaken the wad, and resumed his flight.
I cleaned, and later ate him, after we pooled our collective rabbits, squirrels, and pheasants from that season. It was just enough to feed the four of us, and one of our fathers-we had much to learn about hunting. The grouse ate well.
I suppose a real sport would have set the grouse free after the discovery of poor marksmanship and accidental grounding of the bird. But, I didnt and dont subscribe to a notion of accidents not being sporting. I collect the birds I hit with the car (always an accident) and one time witnessed a long CB radio antenna whip a grouse out of the sky as a truck went past. The truck never slowed a bit.
That grouse ate well, too.
Hang a gun out the window of a vehicle and shoot a bird and Ive got no time for you. Stop the truck, get out, and hunt a bird you saw run across the road is different.
Steve Bodio wrote eloquently on this exact subject in On the Edge of the Wild, in the chapter Evolution of a Hunter.

Best,
Ted