Belted magnum

The term belted magnum[1][better source needed] or belted case refers to any cartridge, but generally a rifle cartridge, with a shell casing that has a pronounced "belt" around its base that continues 2–4 mm (0.079–0.157 in) past the extractor groove.

Non-shouldered (non-"bottlenecked") magnum rifle cartridges especially could be pushed too far into the chamber and thus cause catastrophic failure of the gun when fired with excessive headspace.

The addition of the belt to the casing prevented over-insertion, while allowing smoother feeding from a box magazine compared to a rimmed cartridge.

Many cartridge designs of the last century include this belt, but do not really require it.

Since the beginning of the 21st century, there has been an ever growing trend toward designing beltless magnum cartridges, virtually all of which are heavily shouldered designs that obviate the original motivation for a belt.