The 17 Hornady Magnum Rimfire (17 HMR) is a rimmed, bottlenecked rimfire rifle cartridge featuring a standard maximum bullet diameter of 0.172 inches (4.37 mm). The maximum case length is 1.058 inches (26.87 mm), and the maximum overall cartridge length is restricted to 1.349 inches (34.26 mm) to ensure compatibility with standard rimfire magnum magazines. The case utilizes a rim diameter of 0.286 inches (7.26 mm) and maintains a uniform straight body diameter of 0.238 inches (6.05 mm) from the base to the 25 degree shoulder. Ammunition for this caliber is most commonly found in lightweight 17 grain and 20 grain bullet weights. Exact dimensions and operating pressures can vary slightly depending on manufacturing tolerances and whether you reference American SAAMI specifications or European C.I.P. standards.
17 HMR Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.172 in (4.37 mm) | SAAMI | Standard for .17 caliber rimfire projectiles. |
| Case Length | 1.058 in (26.87 mm) | SAAMI | Maximum case length. |
| Overall Cartridge Length | 1.349 in (34.26 mm) | SAAMI | Maximum overall length for standard rimfire magnum magazines. |
| Rim Diameter | 0.286 in (7.26 mm) | SAAMI | Maximum rim diameter. |
| Case Diameter (Base) | 0.238 in (6.05 mm) | SAAMI | Measured just above the rim. |
| Shoulder Diameter | 0.238 in (6.05 mm) | SAAMI | Features a 25 degree shoulder angle. |
| Neck Diameter | 0.190 in (4.83 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | 0.238 in (6.05 mm) | SAAMI | Uniform with the lower case body due to the straight wall prior to the shoulder. |
| Case Capacity | ~ 7.0 gr H2O | Industry Standard | Varies slightly based on the brass manufacturer. |
| Maximum Pressure | 26,000 psi | SAAMI | Governed by SAAMI specifications for rimfire magnum rifles. |
Understanding The 17 HMR Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the 17 HMR, this is specified as 0.172 inches. This tiny dimension allows the cartridge to achieve incredible velocities, resulting in a remarkably flat trajectory for a rimfire round.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 1.058 inches. This length provides the necessary internal volume to hold slow burning powder charges that maximize the velocity of the lightweight projectile.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 1.349 inches. OAL directly influences whether a cartridge will feed properly through bolt action and semi automatic magazines originally designed for the .22 WMR.
- Rim Diameter: The diameter of the flange at the very bottom of the case measuring 0.286 inches. The firearm extractor hooks onto this rim to pull the spent casing out of the chamber. The rim also contains the impact sensitive priming compound.
- Case Diameter: The width of the cartridge body at the base. At 0.238 inches, the case body matches its parent cartridge, the .22 WMR.
- Shoulder Diameter: The width of the case where it begins to angle inward toward the neck. The 17 HMR utilizes a steep 25 degree shoulder to bottleneck the wide case down to the tiny 0.172 inch bullet.
- Maximum Pressure: The peak internal pressure generated when the cartridge is fired. Standard SAAMI limits set this at 26,000 psi, which is significantly higher than standard .22 Long Rifle limits.
17 HMR Cartridge Dimensions In Inches And Millimeters
For engineers, gunsmiths, and international shooters, below are the primary 17 HMR measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Max) | Millimeters (Equivalent) |
| Bullet Diameter | 0.172 in | 4.37 mm |
| Case Length | 1.058 in | 26.87 mm |
| Overall Length | 1.349 in | 34.26 mm |
| Rim Diameter | 0.286 in | 7.26 mm |
| Base Diameter | 0.238 in | 6.05 mm |
| Shoulder Diameter | 0.238 in | 6.05 mm |
| Neck Diameter | 0.190 in | 4.83 mm |
17 HMR Case Dimensions
The 17 HMR is defined by a rimmed, bottlenecked case. The official maximum case length is 1.058 inches (26.87 mm). The base diameter measures 0.238 inches, and the rim extends wider to 0.286 inches.
The case is essentially a .22 Winchester Magnum Rimfire (.22 WMR) case that has been necked down to accept a 0.172 inch projectile. Because the case was designed to operate at 26,000 psi, it features thicker brass walls than standard .22 LR cases. The bottleneck design is rare for rimfire cartridges but is highly effective at increasing powder capacity relative to the bore size, allowing the expanding gases to push the tiny bullet to velocities exceeding 2,550 feet per second.
17 HMR Bullet Diameter
The standardized maximum bullet diameter for the 17 HMR is 0.172 inches (4.37 mm).
Because the projectile is so incredibly small and travels at such high velocities, it is highly susceptible to wind drift and requires precision rifling to stabilize. The standard 17 HMR barrel features a groove diameter of 0.172 inches and a bore or land diameter of 0.168 inches. Rifles chambered in this caliber typically utilize a 1 in 9 inch twist rate to properly stabilize the high velocity 17 grain and 20 grain bullets.
17 HMR Overall Length
The SAAMI maximum overall cartridge length (OAL) for the 17 HMR is 1.349 inches (34.26 mm). This number is a hard limit designed to guarantee that the cartridge will fit perfectly inside standard rimfire magnum magazines.
Typical factory cartridge length varies slightly based on the bullet profile. The most popular load for the 17 HMR features a 17 grain polymer tipped V-MAX bullet. This sharp, aerodynamic tip pushes the overall length very close to the 1.349 inch maximum. Jacketed hollow point variants or heavier 20 grain options may measure slightly shorter to ensure proper feeding geometry up the feed ramp of the rifle.
17 HMR Chamber And Cartridge Dimensions
The relationship between the 17 HMR cartridge and the firearm chamber is critical for reliable ignition and extraction. The 17 HMR headspaces entirely on its rim, not on its bottleneck shoulder.
This means the front face of the 0.050 inch thick brass rim physically stops against a machined ledge at the rear of the barrel chamber. Because the firing pin must crush the rim to ignite the priming compound, headspace tolerances are meticulously controlled. If a rifle has excessive headspace, the firing pin will push the cartridge forward rather than crushing the rim, resulting in a failure to fire.
17 HMR Dimensions vs Similar Cartridges
To understand the 17 HMR size profile, it is helpful to compare it against other popular rimfire cartridges.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Rim Diameter | Maximum Pressure | Source |
| 17 HMR | 0.172 in | 1.058 in | 1.349 in | 0.286 in | 26,000 psi | SAAMI |
| .22 WMR | 0.224 in | 1.055 in | 1.350 in | 0.286 in | 24,000 psi | SAAMI |
| 17 Mach 2 | 0.172 in | 0.714 in | 1.000 in | 0.278 in | 24,000 psi | SAAMI |
| .22 LR | 0.226 in | 0.613 in | 1.000 in | 0.278 in | 24,000 psi | SAAMI |
17 HMR vs .22 WMR Dimensions
The 17 HMR was developed in 2002 by Hornady directly from the .22 Winchester Magnum Rimfire (.22 WMR). While they share the same parent case, their physical profiles and capabilities are vastly different.
- Bullet Diameter: The 17 HMR utilizes a tiny 0.172 inch bullet. The .22 WMR utilizes a larger 0.224 inch bullet.
- Case Shape: The 17 HMR is a bottlenecked cartridge, narrowing at a 25 degree shoulder. The .22 WMR is a straight walled cartridge.
- Dimensions: Both utilize the exact same 0.286 inch rim diameter, 0.238 inch base diameter, and effectively the same 1.350 inch overall length class. This dimensional similarity allows rifle manufacturers to offer the same firearm models in both calibers by simply changing the barrel and making minor adjustments to the magazine feed lips.
17 HMR SAAMI vs C.I.P. Dimensions
Cartridge dimensions and safe pressure limits are strictly governed by SAAMI in the United States and C.I.P. in Europe.
SAAMI lists the maximum average pressure for the 17 HMR at 26,000 psi, measured via conformal piezoelectric transducers. Hornady engineered the cartridge specifically to SAAMI specifications upon its release in 2002. C.I.P. also standardized the cartridge for the European market. The physical dimensional specifications for the cartridge are functionally identical between the two bodies to ensure global compatibility. Ammunition manufactured to SAAMI specifications is considered safe and standard for use in properly chambered firearms globally.
17 HMR Bullet Weight And Dimensions
The 17 HMR was optimized entirely around extreme velocity and explosive terminal performance on small varmints. The caliber is highly standardized around two specific bullet weights:
- 17 grain: The original and most popular weight, typically featuring a polymer tip (V-MAX). These bullets are highly aerodynamic for their size and achieve velocities of 2,550 feet per second. The long polymer tip maintains the necessary overall length for proper magazine feeding.
- 20 grain: A slightly heavier jacketed hollow point or soft point bullet designed for deeper penetration on game like coyotes or foxes. Because it lacks a long polymer tip, the bullet seats differently within the case but maintains the required external cartridge dimensions.
Unlike centerfire ammunition, rimfire cartridges cannot be reloaded. Shooters must rely entirely on factory ammunition configurations, making these two standard weights the universal dimensional reference points for the caliber.
Why 17 HMR Dimensions Matter
Understanding the specific 17 HMR measurements is essential for several practical reasons.
- Cleaning Equipment: Because the bore diameter is only 0.172 inches, standard .22 caliber cleaning rods and brushes will not fit inside a 17 HMR barrel. Shooters must purchase dedicated .17 caliber cleaning equipment to maintain their rifles safely without damaging the rifling.
- Magazine Compatibility: The 1.349 inch overall length and 0.286 inch rim diameter allow many firearms to share magazines between 17 HMR and .22 WMR rifles, though checking for specific caliber designations on the magazine follower is always recommended for optimal reliability.
- Firearm Maintenance: The bottleneck case design and 26,000 psi operating pressure create unique extraction dynamics. Rifle chambers must be kept exceptionally clean, as carbon fouling in the narrow shoulder region can cause cases to stick or split upon extraction.
Manufacturer Specifications vs Independent Measurements
If you use calipers to measure factory 17 HMR ammunition from companies like Hornady, CCI, or Winchester, the numbers will rarely match the SAAMI maximum specifications exactly.
SAAMI publishes maximum allowable dimensions to ensure absolute safety and interoperability across all firearm brands. Ammunition manufacturers purposefully produce their cases slightly smaller than these maximums. For example, the maximum case length is 1.058 inches, but measuring a factory cartridge might reveal a case length of 1.050 inches. This built in negative tolerance margin guarantees that the ammunition will chamber smoothly in the field without jamming in tight match grade chambers.
Common Questions
What are the dimensions of the 17 HMR?
The key maximum dimensions are a bullet diameter of 0.172 inches, a case length of 1.058 inches, and an overall cartridge length of 1.349 inches.
What is the 17 HMR case length?
The maximum SAAMI case length is 1.058 inches (26.87 mm).
What is the 17 HMR overall length?
The maximum overall length (OAL) is 1.349 inches (34.26 mm), designed to fit standard rimfire magnum magazines.
What is the 17 HMR bullet diameter?
The SAAMI maximum bullet diameter is 0.172 inches.
What is the 17 HMR rim diameter?
The rim diameter measures 0.286 inches, identical to its parent case, the .22 WMR.
What is the 17 HMR case diameter?
The case diameter at the base is 0.238 inches, featuring a straight body wall up to a 25 degree bottleneck shoulder.
What is the maximum pressure for the 17 HMR?
The SAAMI maximum average pressure is strictly capped at 26,000 psi.
How do 17 HMR and .22 WMR dimensions compare?
They share the exact same case base diameter, rim diameter, and overall length. However, the 17 HMR bottlenecks down to hold a much smaller 0.172 inch bullet, whereas the .22 WMR is a straight walled case holding a 0.224 inch bullet.
Can you shoot 17 HMR out of a .22 WMR rifle?
No. While the cartridge base will fit the bolt face, a 0.172 inch bullet will rattle dangerously down a 0.224 inch bore, and the bottleneck case will rupture inside a straight walled chamber.