What is the difference between rimfire and centerfire ammunition?
The difference is where the priming compound sits. In a rimfire cartridge, the priming compound is spun into the hollow rim at the base of the case, and the firing pin fires the cartridge by crushing that rim against the edge of the chamber. In a centerfire cartridge, the priming compound is held in a separate, replaceable primer seated in a pocket at the center of the case head, and the firing pin strikes that primer.
Everything else about the two systems follows from that one design choice. Because a rimfire case has to be thin enough for the firing pin to crush, rimfire cartridges are limited to lower chamber pressures and, today, to small calibers such as .22 LR and .17 HMR. Because a centerfire case is thick at the base and its primer can be pushed out and replaced, centerfire cases can be built for much higher pressures and can be reloaded. Almost every handgun, rifle and shotgun cartridge beyond the small rimfires is centerfire.
You can tell a fired case apart at a glance: a rimfire firing pin leaves a notch or dent at the edge of the base, while a centerfire firing pin leaves a round dimple in the primer at the center.
How does rimfire ignition work?
A rimfire case is drawn from thin brass (sometimes plated) into a tube with a hollow, folded rim at its base. During manufacture, a wet priming mixture is placed in the case and spun so that it collects inside the rim. Once dry, it is sensitive to impact.
When the trigger is pulled, the firing pin strikes the rim at one point and pinches it against the breech face of the barrel. That crush ignites the priming compound, which ignites the powder charge, and the expanding gas drives the bullet down the barrel.
Two practical consequences follow:
- Even distribution matters. The firing pin crushes only one spot on the rim. If the priming compound at that spot is thin, the round may not fire. Occasional rimfire misfires are a known characteristic of the system rather than a sign of a defective firearm, as covered in .22 LR plinking and target loads compared.
- Dry firing can matter. With no cartridge in the chamber, some rimfire firing pins can strike the edge of the chamber itself. Many rimfire firearm manuals address dry firing specifically, and snap caps made for rimfire exist for that reason. The owner's manual for the specific firearm is the authority here.
How does centerfire ignition work?
A centerfire case has a solid, thick base with a primer pocket in the center. The primer is a small metal cup containing priming compound, pressed into that pocket. When the firing pin dents the primer cup, the compound is crushed against an anvil and ignites; the flame passes through a flash hole into the case and ignites the powder.
Two primer systems are in use:
| System | Where the anvil is | Flash holes | Where it is common |
|---|---|---|---|
| Boxer | Inside the primer | One, centered | Most commercial ammunition made in North America |
| Berdan | Formed into the case | Two or more, off center | Much European and military ammunition, including a lot of steel-case ammunition |
The Boxer design is the one handloaders work with, because a single central flash hole lets a decapping pin push the spent primer out from inside the case.
How do rimfire and centerfire compare side by side?
| Attribute | Rimfire | Centerfire |
|---|---|---|
| Priming | Compound inside the case rim | Separate primer at the center of the case head |
| Case base | Thin, so the rim can be crushed | Thick and solid |
| Chamber pressure | Lower | Ranges from low to very high |
| Typical calibers today | .17 and .22 caliber, plus a few others | Nearly all handgun, rifle and shotgun cartridges |
| Reloadable | No (in practice) | Yes, for Boxer-primed brass cases |
| Components per cartridge | Case, priming, powder, bullet | Case, primer, powder, bullet |
| Misfire behavior | Occasional misfires are a known trait | Misfires are reported less often |
Can rimfire or centerfire cases be reloaded?
Centerfire cases with Boxer primers can be reloaded; rimfire cases cannot, in any practical sense.
Reloading a centerfire case means pushing out the spent primer, resizing the case, seating a new primer, adding a measured powder charge and seating a new bullet. Brass cases can usually go through that cycle several times before they wear out. Berdan-primed and steel cases are much harder to reload, which is one reason that topic comes up in steel case vs brass case.
A rimfire case has no separate primer to replace. Its priming compound was spun into the rim at the factory, and firing deforms the rim where the pin struck. There is no standard component or tool for re-priming it, so rimfire cases are generally treated as single-use.
Which calibers are rimfire and which are centerfire?
Common rimfire cartridges in current production:
| Cartridge | Example load (manufacturer's published figure) | Notes |
|---|---|---|
| .22 LR | CCI Mini-Mag 40gr at 1,235 fps | The most common rimfire cartridge worldwide; introduced in 1887 |
| .22 WMR (.22 Magnum) | CCI Maxi-Mag 40gr JHP at 1,875 fps | A longer, higher-pressure .22 rimfire case |
| .17 HMR | Hornady 17gr V-MAX at 2,550 fps | A .22 WMR case necked down to .17 caliber |
| .17 WSM | Varies by load | Higher pressure than .17 HMR; less common |
| .22 Short and .22 Long | Varies by load | Older, shorter cases that .22 LR largely replaced |
Velocities are the manufacturers' published figures, generally from rifle-length test barrels; handguns produce less.
Common centerfire cartridges include every major handgun cartridge (9mm, .45 ACP, .38 Special), every common rifle cartridge (5.56 NATO and .223 Remington, .308 Winchester, 6.5 Creedmoor) and modern shotgun shells, which also use a primer at the center of the base.
Rimfire cartridges larger than .22 caliber were used in the 19th century, including the .44 Henry and the .56-56 Spencer, but centerfire cartridges replaced them in that size range.
How do pressure and velocity differ?
Because the rimfire case must stay thin enough to crush, rimfire cartridges run at lower maximum pressures than most centerfire cartridges. The table lists maximum pressure figures as published in standard cartridge references (SAAMI figures for the centerfire rows):
| Cartridge | Type | Published maximum pressure |
|---|---|---|
| .22 LR | Rimfire | 24,000 psi |
| .22 WMR | Rimfire | 24,000 psi |
| .17 HMR | Rimfire | 26,000 psi |
| .17 WSM | Rimfire | 33,000 psi |
| 9mm Luger | Centerfire handgun | 35,000 psi |
| .223 Remington | Centerfire rifle | 55,000 psi |
| .308 Winchester | Centerfire rifle | 62,000 psi |
In general terms, rimfire loads range from subsonic .22 LR (around 1,000 fps or less) up to roughly 2,500–3,000 fps for the .17 caliber magnum rimfires with very light bullets. Centerfire rifle cartridges routinely push much heavier bullets at 2,500–3,000 fps and beyond. Rimfire bullets are also light: .22 LR bullets are commonly around 30–40 grains, while centerfire rifle bullets commonly range from about 55 to 180 grains. See what does grain mean? for the unit.
Why is rimfire ammunition cheaper to make?
Rimfire is less expensive to manufacture per round than centerfire for structural reasons, not because of any one brand or market condition:
- One fewer component. There is no separate primer cup, anvil or primer-seating step; the priming compound goes directly into the case.
- Less material. A thin, small case and a small, light bullet use far less brass, lead and powder than a centerfire cartridge.
- Simple bullets. Much .22 LR uses a plain or plated lead bullet rather than a jacketed one.
- Very high production volume. .22 LR is made in very large quantities on highly automated lines, which spreads fixed manufacturing costs across many rounds.
The same structure explains why rimfire is not reloaded: the savings come from a case that was never designed to be used twice.
How can you compare rimfire and centerfire costs?
Cost per round changes with the market, so this page does not freeze a figure. Tracked prices and history are on the caliber pages:
- .22 LR prices and .17 HMR prices
- Cheapest calibers to shoot, which ranks tracked calibers by cost per round
- .22 LR plinking and target loads compared, which covers how .22 LR load types differ
Related articles
- .22 LR plinking and target loads compared
- Steel case vs brass case
- Subsonic vs supersonic
- Bullet types explained
Sources
- Rimfire ammunition — Wikipedia — Rim priming, pressure limits, history and current rimfire cartridges
- Centerfire ammunition — Wikipedia — Boxer and Berdan primer systems
- CCI Rimfire Ammunition — Mini-Mag and Maxi-Mag published velocities
- Hornady 17 HMR 17 gr V-MAX — Published velocity
- SAAMI Technical Information — Industry pressure standards