The .22 Long Rifle (.22 LR) requires specific chamber dimensions to safely ignite its rimfire primer and accurately stabilize its unique heeled bullet. The standard SAAMI Sporting chamber features a base diameter of .2307 inches (5.86 mm), a mouth diameter of .2270 inches (5.77 mm), and a generous length to the throat of .818 inches (20.78 mm). Because the cartridge headspaces on the rim rather than the case mouth or shoulder, the chamber features a critical rim cavity depth of .043 inches (1.09 mm). While the Sporting chamber maximizes reliability across all ammunition types, precision firearms often utilize tighter Match or Bentz chamber specifications. Exact measurements depend heavily on the specific reamer profile chosen by the barrel manufacturer.
.22 LR Chamber Dimensions
| Dimension | Specification | Source | Notes |
| Chamber Base Diameter | .2307 in (5.86 mm) | SAAMI Sporting | Measured at the extreme rear of the chamber. |
| Chamber Mouth Diameter | .2270 in (5.77 mm) | SAAMI Sporting | Measured at the front of the chamber before the throat. |
| Length to Throat | .818 in (20.78 mm) | SAAMI Sporting | Distance from the rim to the start of the throat. |
| Headspace (Rim Depth) | .043 in (1.09 mm) | SAAMI | Minimum depth of the rim cut; dictates headspace. |
| Rim Cavity Diameter | .288 in (7.32 mm) | SAAMI | Diameter of the recess machined for the cartridge rim. |
| Bore Diameter | .217 in (5.51 mm) | SAAMI | Internal diameter of the barrel lands. |
| Groove Diameter | .222 in (5.64 mm) | SAAMI | Internal diameter of the barrel grooves. |
| Twist Rate | 1:16 | SAAMI | Standard rifling twist for stabilizing 40 grain bullets. |
Understanding The .22 LR Chamber Dimensions
- Chamber Base Diameter: The width of the chamber at the very rear, where it supports the base of the brass case. In a Sporting chamber, this is cut to .2307 inches to allow dirty or fouled ammunition to feed reliably.
- Chamber Mouth Diameter: The width of the chamber at the forward edge before the rifling begins. It narrows slightly to .2270 inches to help center the bullet.
- Length to Throat: The distance from the rim cavity to the point where the chamber transitions into the rifling. At .818 inches, the Sporting chamber has a very long “jump,” ensuring the bullet does not jam into the lands upon chambering.
- Headspace (Rim Depth): Measuring a minimum of .043 inches, this is the depth of the pocket cut for the cartridge rim. The .22 LR headspaces entirely on this rim.
- Rim Cavity Diameter: The width of the machined pocket that accepts the rim of the cartridge (.288 inches).
- Bore and Groove Diameter: The internal barrel measurements. The lands (bore) measure .217 inches, while the grooves measure .222 inches. The .2255 inch soft lead bullet easily swages into these dimensions to create a tight gas seal.
.22 LR Chamber Dimensions In Inches And Millimeters
For gunsmiths, machinists, and barrel manufacturers, below are the primary .22 LR SAAMI Sporting chamber measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Sporting) | Millimeters (Equivalent) |
| Chamber Base Diameter | .2307 in | 5.86 mm |
| Chamber Mouth Diameter | .2270 in | 5.77 mm |
| Length to Throat | .818 in | 20.78 mm |
| Headspace (Rim Depth) | .043 in | 1.09 mm |
| Rim Cavity Diameter | .288 in | 7.32 mm |
| Bore Diameter | .217 in | 5.51 mm |
| Groove Diameter | .222 in | 5.64 mm |
The Three Types of .22 LR Chambers
Unlike most centerfire rifle cartridges that rely on a single universal chamber specification, the .22 LR is cut using several different chamber reamers depending on the intended application of the firearm.
- SAAMI Sporting Chamber: This is the loosest and longest chamber design. It is used in mass produced hunting rifles, plinking pistols, and high volume semi automatic firearms (like a standard Ruger 10/22). It guarantees reliable feeding and extraction even when the gun is heavily fouled with carbon and wax bullet lube.
- Bentz Chamber: Developed specifically for match grade semi automatic rifles. The Bentz chamber is tighter than a Sporting chamber but looser than a Match chamber. It provides excellent bullet alignment for improved accuracy without causing the frequent feeding jams that a true Match chamber would create in an autoloading action.
- SAAMI Match Chamber: The tightest and shortest standard specification. Used exclusively in precision bolt action target rifles (like Anschutz or Winchester 52-D rifles). The chamber is so short that the bullet physically presses into the rifling upon closing the bolt.
.22 LR Sporting vs Match vs Bentz Dimensions
Comparing the exact dimensions of these three common chamber reamers reveals why they perform so differently.
| Chamber Type | Base Diameter | Mouth Diameter | Length to Throat | Target Application |
| SAAMI Sporting | .2307 in | .2270 in | .818 in | General purpose, hunting, and reliable semi autos. |
| Bentz Chamber | .2270 in | .2255 in | .690 in | Match grade semi automatic rifles. |
| SAAMI Match | .2267 in | .2248 in | .643 in | Precision bolt action target rifles. |
Notice that the SAAMI Match chamber has a length to the throat of only .643 inches, compared to the .818 inch length of the Sporting chamber. Because a standard .22 LR cartridge case is .613 inches long, the Match chamber leaves virtually zero “freebore.” The bullet engages the rifling immediately, which drastically improves accuracy but makes extracting an unfired round difficult.
.22 LR Chamber Dimensions vs Cartridge Dimensions
To understand how the cartridge fits inside the barrel, you must compare the maximum cartridge dimensions to the minimum chamber dimensions.
The maximum base diameter of a .22 LR cartridge case is .226 inches. In a SAAMI Sporting chamber, the base is cut to .2307 inches. This provides roughly 0.0047 inches of clearance, which allows the cartridge to drop freely into the chamber even if it is coated in grit. In a SAAMI Match chamber, the base is cut to .2267 inches, leaving a microscopic 0.0007 inches of clearance. This tight fit ensures the cartridge cannot wobble or lay off-center during ignition, which is critical for putting bullets through the same hole at 50 yards.
.22 LR Headspace and Rim Dimensions
Headspace in a .22 LR firearm is entirely controlled by the rim cavity cut into the breech face or barrel.
SAAMI specifies the minimum rim cavity depth at .043 inches. This corresponds directly to the maximum rim thickness of a .22 LR cartridge, which is also .043 inches. If a chamber has excessive headspace (for example, a rim cavity cut to .050 inches), the cartridge will slide forward when the firing pin strikes it. This cushions the blow, leading to light primer strikes and misfires. Conversely, if the headspace is too tight, closing the bolt could crush the rim and accidentally detonate the pressure sensitive priming compound before the bolt is fully locked.
CCI Stinger Chamber Compatibility
One of the most critical safety issues regarding .22 LR chamber dimensions involves hyper velocity ammunition, specifically the CCI Stinger.
The CCI Stinger achieves higher velocities by using a lighter 32 grain bullet paired with a longer brass case. A standard .22 LR case is .613 inches long, but the Stinger case is .702 inches long.
- In a Sporting Chamber (.818 in length): The longer Stinger case fits perfectly and fires safely.
- In a Bentz or Match Chamber (.690 in or .643 in length): The Stinger case is physically longer than the chamber itself. Chambering a Stinger forces the brass case mouth into the barrel rifling. Upon firing, the crimped brass cannot expand to release the bullet, resulting in a dangerous pressure spike that can rupture the case or damage the firearm.
Never fire CCI Stingers or similarly lengthened cases in firearms with Bentz or Match chambers.
SAAMI vs C.I.P. .22 LR Chamber Dimensions
Cartridge and chamber specifications are governed by SAAMI in the United States and C.I.P. in Europe.
While the two organizations largely agree to ensure global ammunition compatibility, European C.I.P. specifications for the .22 LR bore are notably tighter. SAAMI lists the standard .22 LR bore diameter at .217 inches. C.I.P. allows for a tighter minimum bore diameter of .212 inches. High end European rimfire manufacturers like CZ often utilize these tighter C.I.P. specifications, which is why European bolt action rifles are famously accurate but sometimes require specialized cleaning rods, as a standard American .22 caliber cleaning jag may fit too tightly in the bore.
Why .22 LR Chamber Dimensions Matter
Understanding your specific .22 LR chamber dimensions is essential for several practical reasons.
- Ammunition Selection: If you own a rifle with a Bentz chamber, you must avoid hyper velocity ammunition with elongated cases to prevent pressure spikes.
- Accuracy Potential: A Sporting chamber will never rival a Match chamber in absolute accuracy because the bullet has to “jump” a long distance before engaging the rifling, which allows the soft lead projectile to enter the bore slightly crooked.
- Reliability: Match chambers are notoriously unreliable in semi automatic actions. The tight tolerances cause the wax lubricant found on premium .22 LR target ammo to build up rapidly, causing failures to extract after only a few magazines.
- Lead Shaving: If the transition from the chamber mouth to the rifling is cut poorly or has burrs, it will shave lead off the side of the bullet as it fires, ruining the aerodynamics of the projectile and heavily fouling the barrel.
Manufacturer Specifications vs Independent Measurements
If a gunsmith uses a bore micrometer to measure the chamber of a factory mass produced rifle, the numbers will rarely match the exact SAAMI Sporting chamber drawing down to the ten-thousandth of an inch.
Chambering reamers are cutting tools made of high speed steel or carbide, and they wear down over time. A barrel chambered with a brand new reamer will have slightly larger internal dimensions than a barrel chambered with a reamer that has already cut 1,000 chambers. Firearms manufacturers routinely replace reamers once they approach the minimum allowable SAAMI tolerance, ensuring every rifle leaving the factory is safe and reliable, even if the exact chamber dimensions fluctuate slightly from batch to batch.
Common Questions
What are the standard .22 LR chamber dimensions?
The SAAMI Sporting chamber features a .2307 inch base diameter, a .2270 inch mouth diameter, and a length of .818 inches to the throat.
What is a Bentz chamber?
A Bentz chamber is a specialized .22 LR chamber designed specifically for match grade semi automatic rifles. It is tighter than a Sporting chamber for better accuracy, but looser than a Match chamber to ensure reliable feeding and extraction.
What is a Match chamber in .22 LR?
A Match chamber is the tightest specification available, featuring a short .643 inch length to the throat. The bullet engages the rifling immediately upon chambering, resulting in maximum precision for bolt action target rifles.
How does a .22 LR cartridge headspace?
The .22 LR headspaces entirely on the rim. The chamber features a specific recessed rim cavity measuring a minimum of .043 inches deep to trap the rim against the bolt face.
What is the bore diameter of a .22 LR barrel?
The standard SAAMI bore diameter (measured across the lands) is .217 inches, while the groove diameter measures .222 inches.
Can I shoot CCI Stingers in a Match or Bentz chamber?
No. The brass case on a CCI Stinger is longer than standard .22 LR brass. It will jam into the rifling of tight Match or Bentz chambers, causing a dangerous pressure spike.
What is the .22 LR headspace tolerance?
The ideal headspace dimension (rim depth) is .043 inches for the GO gauge, with the NO-GO gauge typically measuring .045 or .046 inches depending on the manufacturer.
Why are CZ .22 LR barrels so tight?
European manufacturers like CZ adhere to C.I.P. minimum bore dimensions, which allow for a tighter .212 inch bore compared to the slightly looser American SAAMI specification.