Pigeons and upland birds:
I place the bird on its back in my left hand and put one wing under my index finger and the other wing under my the baby finger. My 2 middle fingers straight up the center of the back.
Then place my right hand palm down on the breast, and poke my thumb through the skin up under the breast bone.
I then loosely grasp the breast and pry the breast upwards until it is dis-lodged all the way to the wings.
Now gripping tightly what ever is in each hand twist and pull apart.
You should have a breast in your right hand and everything else in your left.
Toss the left hand stuff away. Peel the skin with feathers off the breast. Your done.
Total time 6-8 seconds.
Done it that way for years. Hundreds of birds.
My buddy and I shoot pigeons as he is from France and luvs to eat them ( I don't mind the winged rats either) I can clean a pile of them in a couple minutes.
I started to do it this way when I pulled the legs off a few grouse and then had a mess to fix up as the breast was still attached to the rest of the bird.