An improved method of machines grooves forming Pearson notches in a pattern on hollow shell casings for munitions for at least one of increased functionality and/or performance. Rather than running a broach through a hollow casing, a CNC lathe with a multi-axis tool with cutting implement can precisely locate and form grooves along either an interior or an exterior surface of a hollow shell casing.

A precision case holder engages the extraction groove of the rim of a straight wall case and established a fixed distance between a base of the case and a precision forward surface of the holder. The case may then be inserted into a case trimmer and the holder establishes a repeatable distance between the base of the case and a cutting tool in the case trimmer. The holder includes a tapered slot with edges which engage the extraction groove and a threaded piston which is tightened against the base of the case. The case slides into the tapered slot until the taper resists further sliding, and the piston is tightened to retain the case.

A case mouth trimmer and chamferer includes a clear sliding sleeve covering windows in a barrel portion to capture trimmings. The case mouth chamfer tool may be fixed to a micrometer dial threadedly engaging the barrel. A case adapter bearing is fixed to the barrel to position cases. An end m ill is used trim the case length or a case mouth chamfer tool is adjusted to cut an inside chamfer and the micrometer dial is rotated to adjust the position of the end mill or the case mouth chamfer tool with respect to the case adapter bearing to precisely adjust the amount of material cut from the case. An adjustable cutter holder member slides in a dovetail, is adjusted by advancing and retreating a screw, and is held in place by a set screw. The case adapter bearing is easily changed to chamfer different cases.