Every cartridge in this series is ignited by a primer, but the primer sits in different places. In a rimfire it is spun into the rim of the case. In a centerfire it sits in a separate cup in the middle of the case head. That one difference explains most of what separates the .22 LR from the .500 Nitro Express.

Rimfire: priming in the rim

A rimfire case is a thin, folded rim filled with priming compound, and the firing pin crushes the rim against the chamber edge to set it off. The case walls have to stay thin enough to be crushed, which limits the pressure the cartridge can handle, and fired rimfire cases cannot be reloaded.

The .22 LR, introduced in 1887, is the best-known rimfire, and CCI's lead round-nose loads are at cci 22lr lead round nose ammo. Lapua, a Finnish maker, builds .22 LR match ammunition for competition shooters, and its loads are at lapua 22lr ammo for sale.

The 5mm Remington Rimfire Magnum is the unusual one, a bottlenecked rimfire that Remington announced in 1969 for its Model 591 and 592 rifles. Remington later dropped the ammunition, but it has since been revived, and current loads are at 5mm remington magnum ammo.

Centerfire: priming in the center

A centerfire case has a separate primer seated in the middle of the case head. The case walls can be thick and strong, so the cartridge can handle far more pressure, and the brass can be reloaded with new primers.

The AR-pattern big bores are all centerfire. The .450 Bushmaster's 250-grain loads are at 450 bushmaster 250 grain ammo. The .458 SOCOM, built on a trimmed .50 Action Express case, has its loads at 458 socom ammo for sale.

The .458 HAM'R, a Wilson Combat design that moves the shoulder of the .458 SOCOM case forward for more capacity, has Wilson Combat's own loads at wilson combat 458 hamr ammo. The .450 Marlin's FMJ loads are at 450 marlin fmj ammo.

The classic dangerous-game cartridges are centerfire as well. The .458 Winchester Magnum, introduced in 1956, is at 458 win mag ammo. The .500 Nitro Express's 570-grain loads are at 500 nitro express 570 grain ammo.

The .500 Jeffery, which fits a magnum-size Mauser 98 action, has soft-point loads at 500 jeffery soft point ammo.

Why it matters at the counter

Rimfire and centerfire cartridges are not interchangeable, even when the bullet diameter looks close. A rifle chambered for .22 LR cannot fire a .223 Remington, though both use a bullet about .22 inch across. Always match the cartridge to the rifle's chambering.

Never fire a cartridge in a rifle that is not marked for it, and confirm current stock and state shipping restrictions before ordering.