Complex sentence: Deer and upland birds are not the only suitable game for the 20 gauge, its very common for a hunter to use this firearm to hunt for squirrels, rabbits, and waterfowl.
Split into simpler sentences: Deer and upland birds are not the only suitable game for the 20 gauge. It's very common for a hunter to use this firearm to hunt for squirrels, rabbits, and waterfowl.