In my experience, hard buckshot, especially copper plated shot, packed in buffering material usually shoots the best patterns. The ordinary soft shot are so beat up by the time they exit the barrel that they fly more randomly. Also, on the rare occasions when I must use buckshot, I like 000 shot. Compared to the 0.33" 00 shot weighing about 54 gr, 000 is .36" diameter and weighs about 68 gr per pellet. It may not sound like much, but that is almost 20% in frontal area and 25% increase in mass. There are fewer of them, but I believe (without conclusive supporting evidence) that they are more effective.

Take care, Tom