Answer
Impact or shock loading in drilling tools can momentarily exceed the static thrust capacity of a retaining ring by several orders of magnitude. The kinetic energy $U = \frac{1}{2} m v^2$ must be absorbed by the elastic and plastic deformation of the ring and groove. In these environments, a 'Heavy Duty' spiral ring with a larger radial wall $b$ is required. Furthermore, the groove depth $d$ should be maximized to provide more shear area. Because impact loads can cause the ring to 'hop' out of the groove due to vibration, a 3-turn ring is often preferred over a 2-turn ring as it provides more surface contact and damping. Material choice is also critical; S66286 (A286) stainless is often used for its high toughness and strength in these high-shock, corrosive environments.
