Rimmed, Rimless, Belted, Rebated: Reading a Cartridge by Its Case

Two cartridges with the same bullet can be completely different rounds, because the case decides how they feed, headspace and fit. Four features explain most of it: the parent case, the rim, the belt and the shoulder.

Parent cases and necking down

New cartridges are usually old cases with a new neck. The 6mm Creedmoor is the 6.5 Creedmoor case necked down to hold a 6mm bullet, and Hornady's loads for it are at hornady 6mm creedmoor ammo. The 6mm Remington began as the .244 Remington, a .257 Roberts case necked down to 6mm, and its loads are at 6mm remington ammo for sale.

The 6.5 Creedmoor itself, whose polymer-tip loads are at 6.5 creedmoor polymer tip ammo, is a slim, efficient case with a sharp 30-degree shoulder, a shape designed to make good use of the powder it holds.

The rim

Most modern cartridges are rimless, with a groove near the base for the extractor. Older designs and break-action rifles often use a rim instead. The 9.3x74R is rimmed, which is what the R stands for, because a rim lets a break-action rifle's extractor lift the case. Its loads are at 9.3x74r ammo.

The 6.5 Carcano is rimless and fires a long 156-grain round-nose bullet, a shape that suited the military bolt rifle it was built for. Those loads are at 6.5 carcano 156 grain ammo. The 6.5x55 is rimless too, and its 140-grain loads, at 6.5x55 140 grain ammo, are among the most common weights.

The belt and the rebate

A belt is a raised ring just ahead of the extractor groove that older magnums used to control headspace, and the Weatherby magnums are the best-known belted family. The 6.5 Weatherby RPM, at 6.5 weatherby rpm ammo, drops the belt and uses a rebated rim instead, which keeps the rim narrower than the case body.

The 6.5 PRC is beltless as well, a way of getting magnum-class performance from a cartridge that fits a short action. Its loads are at 6.5 prc ammo for sale.

Small cases for small rifles

At the other end, the 6mm ARC and the 6.5 Grendel are short cases designed to fit AR-15-sized actions. The ARC's loads are at 6mm arc ammunition. Nosler's Grendel loads are at nosler 6.5 grendel ammo.

Case shapes are exact. Never assume that two cartridges with the same bullet diameter are interchangeable, and confirm current stock and state shipping restrictions before ordering.