I use RST spreader loads for almost all of my Mearns quail hunting and have done so for the last 7 or 8 years. All of this hunting has been done with my Pointers.
Most of these birds are shot under 20 yards and using a light spreader load kills effectively and I believe leaves a bird that is still able to be eaten, even when shot with some of my vintage SXS choked pretty tight.
Spreader loads dont throw some crazy uncontrolled load, they simple help to open up the pattern. I know that this is not a scientific test but my experience from using spreaders in the field.
Its my opinion anyone saying their dog was hit with a stray pellet is using that excuse for shooting a dog.
I never approach my dogs with a low gun where I must bring the gun up over them to shoot a rising bird. I never shoot a bird on the ground. If my dog is on point and the birds flush before I am able to get close to my dog, I dont shoot.
Im sure most guys hunting birds with their dogs follow these same rules.
I do know of several cases where accidents happened or carelessness was involved and dogs were hurt as well as some killed.