A rimmed case carries a rim noticeably wider than the case body, and that protruding flange does two jobs: it stops the cartridge at the correct depth so headspace is set on the rim, and it gives the extractor a generous edge to pull on. The design is simple and forgiving, which is why it dominated early cartridge history and still appears in lever-action rounds like the .30-30 Winchester, break-action rifles, and most rimfire ammunition. Revolver and many shotgun cases share the same idea.

The drawback shows up in box magazines, where a tall rim can hang up on the round beneath it if cartridges are stacked carelessly, a problem called rim lock. That feeding penalty pushed bolt-action and semi-automatic designs toward the flush rimless head, with the semi-rimmed and belted magnum forms offering other ways to manage headspace and extraction. For most modern precision rifles, rimmed cases are the exception rather than the rule.

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