When observing a hole drilled with a gun drill, it is sometimes found that there are annular grooves (annular cuts) in the hole, sometimes periodically on the entire circumference, or on a part of the circumference, and sometimes along the length of the hole, if a hole is required. When the surface roughness is good, this is not allowed. This phenomenon mostly occurs on steel with good soft toughness.
Technical question and answer on the use of cemented carbide gun drill