The .357 Service Magnum is the 2200 production name for what has been called simply .357 Magnum since 1934 — a cartridge that has outlasted the civilization that invented it and shows no sign of retirement. In GLMZ, it occupies a specific and culturally weighted position: it is the round that makes a revolver into something that cannot be dismissed. Where the .38 Service Revolver is the round of the poor and the desperate, the .357 Service Magnum is the round of the deliberate. The person carrying a full-power magnum load in a heavy revolver has made a choice about what they expect to face, and that choice is legible to anyone who knows firearms.

By 2200, the .357 Service Magnum has found an unexpected second life as an anti-augmentation round for civilians who cannot access or afford purpose-built armor-defeating semi-automatic cartridges. The combination of high velocity and heavy projectile options — including Slagworks' dense-core 'Penetrator' loading — gives it genuine capability against subdermal trauma plating at close range that most pocket semi-auto calibers cannot match. Lever-action and bolt-action carbines chambered for it extend that capability to medium range. In the outer districts where Arcturus Civil Security response times are measured in hours, people who can afford a .357 magnum revolver and the ammunition to feed it often sleep better than those who cannot.