LB, I have done it a number of times with the 20 gauge at 50 yards and have done it on camera too. I don't promote that shot only tried it when testing the patterns and what range a 20 would be a true killer but what birds that were hit were not running they were down. They were down and I had to walk up and stand on their head and a couple were toast. Why well I can not tell you theat but have seen the same with other brands as well.
Just remember don't matter what gun your shooting the pattern will never be the same every shot...