This was probably unnoticed by most all of you, but - in the world of Model designations of US small arms cartridges, prior to 1958, “M” numbers were assigned from “T” (test or experimental) series numbers without any attempt at continuity. The two numbers were quite different and it was impossible to connect them without a score card. So, for example, the Cal .30 T291 Match would become the Cal .30 M72 Match.
In 1958, a new designation procedure was adopted wherein test or experimental cartridges were assigned an “XM” number and when (if) they were officially adopted, the “X” was dropped and the new cartridge was standardized with the same basic “M” number. As an example, the 7.62MM XM852 Match became the 7.62MM M852 Match.
But, here’s what you didn’t notice. The subject of this thread, the 7.62MM International Match cartridge, was one of the very few that went from a “T”, to an “XM”, and then to an “M” designation.
This is probably of little interest to most of you, but to me, with an interest in match ammunition and an eye for the unusual, it is one of those little things that makes collecting so interesting.