Ring Lapping
Polishing the inner surfaces of scope rings with an abrasive lapping bar so they contact the tube evenly and grip without inducing stress.
Ring lapping uses a precision bar coated with abrasive compound, run back and forth inside the mounted rings until the high spots are worn away. Machining tolerances and small misalignments mean that out of the box scope rings often touch the tube on only part of their surface, which concentrates clamping force and can pinch or bow the scope body. Lapping increases the contact area so the rings cradle the tube along a broad, even band.
The payoff is a more secure hold that does not deform the maintube, which protects the internals and helps the optic hold zero under recoil. Because lapping is sized to the exact tube diameter of the scope, it also reveals whether your rings are truly aligned before you commit to a final torque spec on the screws. Done carefully, it is cheap insurance against marring or stressing an expensive scope.