Rim Rock Bullets is a family owned and operated business, and takes a personal, hands-on approach to everything they do. They cast lead bullets from virgin lead alloyed with just the right amount of tin and antimony. Rim Rock orders lead in 60 lb bars, 60,000 lbs at a time. By ordering this much lead at once they can make consistently accurate cast lead bullets. At Rim Rock they normally make one particular type of bullet for a week, on one or two machines before going on to another kind or caliber. For instance, if making a run of .38/.357 158 gr. SWC this bullet maybe be run on 4 machines for 10 days, That's in excess of 1 million bullets! Operating like this on one type of bullet at a time is what helps make batches of identical, consistent bullets that you can count on. EVERY time, RIGHT ON TARGET.Rim Rock cast lead bullets are cast at a hardness of BNH 12-15. These bullets are best kept under 1200 fps for optimal performance.