TRUMARK® Steel-Ball Ammo has been chosen for it’s larger size when compared to the 5/16". Although larger, it's not too large. Trumark does not recommend ammo that is larger than 3/8" since it becomes too heavy, and is unsafe if used improperly. About twice the weight of the 5/16" size, Trumark’s 3/8"ammo is still heavy enough for controlling rodents or hunting small game with wrist-braced slingshots in areas where firearms are not appropriate. Perfectly ROUND, Grade A ammo feels good in the pouch, and lets you concentrate on your target as you get ready to shoot. Grade B ammo has a "flat spot" that is found on cheaper metal balls designed for mixing paint in spray cans. Avoid paint can balls...always shoot Grade A Trumark ammo!