With BP shotguns, you can load DOWN- ie. a 16, 20, or 28 gauge load, for shooting small game. You don't have to shoot lots of powder or shot, JUST BECAUSE Its a 12 gauge!
For Dove, you want to be using #8, or #7 1/2 Shot. For Rabbits and Squirrels, where you are not having to shoot through a thick canopy of leaves, use #6 shot. In the early Squirrel Seasons, where the leaves are all on the trees, consider using #5 shot instead, as they carry a bit more pellet energy and penetrate further.
Whether a load "tears" up game " too much " depends entirely on the load used, how much choke is in the barrel, and at what distance you take the shot. YOu will learn these answers about a given gun and load by shooting at various measure distances. Most people are shocked, for instance, to learn that the shot column doe NOT open until about 9 feet from the muzzle, regardless of whether the barrel is choked or not. And, you will be surprised at how open the pattern is at 20 yards- 60 feet. At 30 yards, without choke, its difficult to keep enough shot in a pattern to be sure of killing some game, unless the barrel is choked. So, you will find the limitations of your shotgun simply by shooting at paper targets in 5 yard increments. You will also find out where the POI of a load is, as compared to your POA. That is the primary reason for testing your load on paper- so you know where to aim to put the load on your target. :thumbsup: