Case shapes, materials and the “R” suffix

The metric designation has a frequent appendix on ammunition of Eastern origin: the suffix “R” after the case length — 7.62×54R — marks a rimmed case. It is not a detail for collectors, because the shape of the case head sets where the case rests in the chamber, that is, the headspace of Chapter 10. For the case head there are five shapes — rimmed, semi-rimmed, rimless, belted and rebated rim — and for the body three, cylindrical, tapered or bottleneck; the combinations in use are the ten families of Table 4.3, which come down to four headspacing surfaces: the rim, the shoulder, the belt, the mouth. Before the families, the complete nomenclature, in the two languages in which the shooter will run into it.