Killing pheasants isn't hard if you place the shot in the right place. With that being said the part that gets people is the distance that they try to kill pheasants at. I never shoot 8s at game. And even though I have killed pheasants with 7.5s I do not consider the size to be enough for distance over 25yds. I shoot 6s and 5s out of my 28ga and will shoot up to 4s out of my 20ga if the need occurs.
The bottom line is a pheasant has thick feathers that take some energy to get through. And they provide many bad angles to shoot at. So you either waitfor a better shot angle or beef up your load. I do both plus add in a pointing dog to up my odds. I have personally seen pheasant hit hard[or appeared to be] and bounce off a dirt road and not be there dead when we got there, cause they weren't hit hard enough.
Gselkhunter