1, the internal defects of the projectile material, such as vent cracking, internal shrinkage, etc., can harm its life and use more.  Hardness is proportional to removal rate but inversely proportional to the life time.  Therefore, the hardness is high, the removal speed is faster, but the life time is short and the use is large, so the appropriate hardness should be selected to achieve the desired effect.  

• Adequate density provides a smooth mass that reduces cracking and abrasion during removal.
• Hardness is proportional to the removal rate, the higher the hardness, the faster the removal rate, the greater the cost, the life time will be short, the whole process of production and manufacturing determines the size of the steel shot, the larger the diameter, the roughness of the removal is higher, the work efficiency is also very high, the relative ratio of wear is also very large.