I prefer 7.5 shot in a 1 oz load out of my 20's for doves. You'll get less cripples with the 7.5's. Add in some wind and birds that have been shot a few times and the larger shot will pay off. Remington and Winchester sell Heavy Dove Loads.
I take two boxes (50 rounds) when I go to a shoot, with the goal of filling my limit of fifteen birds with less than one box.
If you are going on a dove shoot in a field with other hunters there is some etiquette.
Dont shoot low birds. This is a big time no no and will get you un invited to future shoots.
Dont skybust. If you can clearly see his beak, hes in range.
Keep and eye on the bird you shot so youre not wandering around flaring birds away from other hunters tring to find your kill.
Dont set up on top of another hunter. We try to have at least 100 yds between hunters at our shoots.