The vast majority of turkey guns are 12 gauges. Sure, other bore sizes will work, but the 12 is king. It offers the most options for ammo, and it’s proven to be the most effective. Even the mighty 10 gauge is outperformed by a modern 3 ½-inch 12-gauge load. They have the same payload, but the 12-gauge generates a higher pressure and so has more velocity and energy. But the most common choice for turkey hunting, and one that’s extremely effective, is the 3-inch magnum 12-gauge.