Final answer:
Shear pins are used to prevent excessive shear stress on a projectile. It is recommended to have 3 shear pins present in this series of projectiles.
Step-by-step explanation:
Shear pins are used to prevent excessive shear stress on a projectile. They act as sacrificial elements that break when subjected to a certain level of force, reducing the risk of damage to the projectile. In this series of projectiles, it is recommended to have 3 shear pins present to ensure adequate protection.