#4 Shot (Lead)
Shot or buckshot is simply lead or steel pellets of varying diameters loaded into shotgun shells (shot shells). The size of the shot dictates the intended use of the shell and is the same for all shotgun gauges (the larger the gauge, the more pellets per shell). The smaller the shot number, the larger the pellets (0000 is largest, #9 is smallest). 0000 to #4 is generally referred to as buckshot and #5 to #9 is called birdshot. The difference between lead and steel pellets is that the lead deforms on impact; steel holds its shape, therefore penetrating further. (Always check with your range before buying regarding any prohibitions against bullet compositions).
One thing to keep in mind is that there is a #4 Buck, which is buckshot as mentioned above. However, there is also a #4 shot, which is birdshot. The difference is in size and intended function. As the names suggest, #4 Buck is intended to bring down a large deer, and so is often used as an effective home defense round, especially at close range. #4 Shot, on the other hand, is much smaller at about 3.30 mm (0.130") in diameter and is primarily used for hunting ducks and turkey. While it can be used for defense purposes, it is not recommended due to the amount of shot and the spread pattern.