The 204 Ruger is a high velocity, rimless, bottlenecked centerfire rifle cartridge featuring a standard maximum bullet diameter of 0.204 inches (5.18 mm). The maximum case length is 1.850 inches (46.99 mm), and the maximum overall cartridge length is restricted to 2.260 inches (57.40 mm) to ensure compatibility with standard short action and AR-15 magazine wells. The case utilizes a rim diameter of 0.378 inches (9.60 mm) and features a base diameter of 0.376 inches (9.55 mm) that tapers to a steep 30 degree shoulder measuring 0.356 inches (9.04 mm). Ammunition for this caliber is most commonly found in lightweight 32 grain and 40 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.
204 Ruger Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.204 in (5.18 mm) | SAAMI | Standard for .20 caliber centerfire projectiles. |
| Case Length | 1.850 in (46.99 mm) | SAAMI | Maximum case length; trim to length is typically 1.840 in. |
| Overall Cartridge Length | 2.260 in (57.40 mm) | SAAMI | Maximum overall length for standard AR-15 and short action magazines. |
| Rim Diameter | 0.378 in (9.60 mm) | SAAMI | Reuses the standard .222 Remington / .223 Remington bolt face. |
| Case Diameter (Base) | 0.376 in (9.55 mm) | SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | 0.356 in (9.04 mm) | SAAMI | Features a steep 30 degree shoulder angle. |
| Neck Diameter | 0.232 in (5.89 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | 0.376 in (9.55 mm) | SAAMI | Uniform with the lower case body just above the rim. |
| Case Capacity | ~ 34.5 gr H2O | Industry Standard | Varies slightly based on the brass manufacturer. |
| Maximum Pressure | 58,500 psi | SAAMI | Governed by SAAMI specifications for high velocity varmint rifles. |
Understanding The .204 Ruger Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the .204 Ruger, this is specified as 0.204 inches. This ultra slender dimension minimizes aerodynamic drag, allowing the projectile to retain velocity exceptionally well downrange.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 1.850 inches. This length provides optimal internal volume for fast burning rifle powders.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 2.260 inches. This length guarantees the cartridge will feed smoothly from standard AR-15 magazines and compact bolt action receivers.
- Rim Diameter: The diameter of the flange at the very bottom of the case measuring 0.378 inches. This matches the standard bolt face of the .223 Remington family, allowing manufacturers to build rifles on existing action tooling.
- Case Diameter: The width of the cartridge body at the base. At 0.376 inches, it mirrors its parent case closely before narrowing sharply.
- Shoulder Diameter: The width of the case where it begins to angle inward toward the neck (0.356 inches). The .204 Ruger utilizes a sharp 30 degree shoulder to maximize powder capacity while maintaining clean headspace control.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging roughly 34.5 grains of water, it holds a massive powder charge relative to the tiny 0.204 inch bore.
- Maximum Pressure: The peak internal pressure generated when the cartridge is fired. Standard SAAMI limits set this at 58,500 psi to achieve blistering velocities near 4,220 feet per second.
.204 Ruger Cartridge Dimensions In Inches And Millimeters
For engineers, reloaders, and international shooters, below are the primary .204 Ruger measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Max) | Millimeters (Equivalent) |
| Bullet Diameter | 0.204 in | 5.18 mm |
| Case Length | 1.850 in | 46.99 mm |
| Overall Length | 2.260 in | 57.40 mm |
| Rim Diameter | 0.378 in | 9.60 mm |
| Base Diameter | 0.376 in | 9.55 mm |
| Shoulder Diameter | 0.356 in | 9.04 mm |
| Neck Diameter | 0.232 in | 5.89 mm |
.204 Ruger Case Dimensions
The .204 Ruger was developed jointly by Hornady and Ruger in 2004, using a necked down and lengthened variant of the .222 Remington Magnum as its parent case. The official maximum case length is 1.850 inches (46.99 mm), with a nominal trim to length for reloaders sitting at 1.840 inches. The base diameter measures 0.376 inches, and the rim extends marginally to 0.378 inches to form the extractor groove.
Because the cartridge is designed to reach extreme velocities exceeding 4,000 feet per second, the case features a sharp 30 degree shoulder angle. This steep shoulder prevents excessive case stretching and helps maintain consistent pressure curves. The internal case capacity is approximately 34.5 grains of water, providing an exceptionally high powder to bore ratio that maximizes energy transfer for varmint hunting.
.204 Ruger Bullet Diameter
The standardized maximum bullet diameter for the .204 Ruger is 0.204 inches (5.18 mm). This dimension introduced a modern revival of .20 caliber centerfire shooting, sitting squarely between traditional .17 caliber rimfires and standard .22 caliber centerfires.
The standard .204 Ruger barrel features a groove diameter of 0.204 inches and a bore or land diameter of 0.194 inches. Firing a 0.204 inch bullet down this barrel forces the copper jacket to engrave tightly into the rifling. Rifles chambered in this caliber typically utilize a 1 in 12 inch twist rate to properly stabilize lightweight varmint bullets ranging from 32 grains to 45 grains.
.204 Ruger Overall Length
The SAAMI maximum overall cartridge length (OAL) for the .204 Ruger is 2.260 inches (57.40 mm). This restriction is a hard limit designed to guarantee that the cartridge will fit inside standard AR-15 magazine wells and short action bolt rifles.
Typical factory cartridge length varies based on the bullet profile. Factory loads featuring polymer tipped bullets (such as Hornady V-MAX) are carefully loaded to sit just under the 2.260 inch limit, maximizing internal powder space while ensuring flawless feeding from standard box magazines.
.204 Ruger Chamber And Cartridge Dimensions
The relationship between the .204 Ruger cartridge and the firearm chamber is engineered for high velocity accuracy. The cartridge headspaces entirely on its 30 degree shoulder.
This means the angled portion of the brass casing physically stops against a matching machined angle inside the barrel chamber. This provides a precise stopping point that centers the tiny bullet perfectly with the bore. Because the cartridge operates at an intense 58,500 psi, handloaders must carefully monitor shoulder bump during resizing to avoid excessive headspace, which can shorten brass life significantly.
.204 Ruger Dimensions vs Similar Cartridges
To understand the .204 Ruger size profile, it is helpful to compare it against other popular small caliber high velocity cartridges.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Base Diameter | Maximum Pressure | Source |
| .204 Ruger | 0.204 in | 1.850 in | 2.260 in | 0.376 in | 58,500 psi | SAAMI |
| .223 Remington | 0.224 in | 1.475 in | 2.260 in | 0.376 in | 55,000 psi | SAAMI |
| .22-250 Rem | 0.224 in | 1.912 in | 2.350 in | 0.473 in | 65,000 psi | SAAMI |
| .17 HMR | 0.172 in | 1.058 in | 1.349 in | 0.238 in | 26,000 psi | SAAMI |
.204 Ruger vs .223 Remington Dimensions
Because both cartridges share the exact same 2.260 inch overall length limit and utilize the same 0.378 inch rim diameter to fit identical AR-15 and bolt action magazines, they are frequently compared.
- Bullet Diameter: The .204 Ruger utilizes a slender 0.204 inch bullet, while the .223 Remington uses a wider 0.224 inch bullet.
- Case Length: The .204 Ruger features a longer 1.850 inch case compared to the 1.475 inch case of the .223 Remington. The Ruger case achieves this by pushing the shoulder forward and lengthening the body.
- Pressure and Velocity: The .204 Ruger operates at a slightly higher maximum pressure of 58,500 psi (compared to 55,000 psi for the .223), allowing it to push lightweight 32 grain bullets at blinding speeds exceeding 4,200 feet per second.
.204 Ruger SAAMI vs C.I.P. Dimensions
Cartridge dimensions and safe pressure limits are governed by SAAMI in the United States and C.I.P. in Europe.
Hornady and Ruger submitted the cartridge to SAAMI upon its release in 2004. SAAMI lists the maximum average pressure for the .204 Ruger at 58,500 psi, measured via conformal piezoelectric transducers. C.I.P. also adopted the cartridge for the international market, listing pressure limits according to European testing standards. The physical dimensional specifications for the cartridge remain identical between both bodies, ensuring that commercial ammunition functions safely in any properly chambered rifle worldwide.
.204 Ruger Bullet Weight And Dimensions
The .204 Ruger was designed exclusively for high velocity varmint hunting, focusing on two primary bullet weights:
- 32 grain: The ultra high velocity champion of the caliber. Leaving the muzzle at roughly 4,220 feet per second, this short bullet leaves maximum internal powder capacity in the 1.850 inch case, producing an explosive terminal effect on small pests.
- 40 grain: A heavier, longer projectile that retains velocity better at extended ranges. To maintain the 2.260 inch overall length restriction, this longer bullet seats deeper into the case, slightly reducing powder volume but providing superior wind resistance past 300 yards.
Why .204 Ruger Dimensions Matter
Understanding the specific .204 Ruger measurements is essential for several practical reasons.
- Cleaning Maintenance: The tiny 0.204 inch bore requires dedicated cleaning rods, jigs, and patches. Standard .22 caliber cleaning equipment will not fit down the barrel without jamming.
- Magazine Interchangeability: Because it shares the 2.260 inch overall length and 0.378 inch rim size with the .223 Remington, many firearms can be converted between the two calibers with a simple barrel swap, though dedicated magazines are often optimized for the slightly different case body taper.
- Throat Erosion: Due to the extreme powder charge burning through a tiny 0.204 inch bore, barrels can experience throat erosion faster than standard .223 rifles if fired rapidly in high volume varmint fields.
Common Questions
What are the dimensions of the .204 Ruger?
The key maximum dimensions are a bullet diameter of 0.204 inches, a case length of 1.850 inches, and an overall cartridge length of 2.260 inches.
What is the .204 Ruger case length?
The maximum SAAMI case length is 1.850 inches (46.99 mm).
What is the .204 Ruger overall length?
The maximum overall length (OAL) is 2.260 inches (57.40 mm), designed to fit standard AR-15 and short action magazines.
What is the .204 Ruger bullet diameter?
The maximum bullet diameter is 0.204 inches (5.18 mm).
What is the .204 Ruger rim diameter?
The rim diameter measures 0.378 inches, matching the standard .223 Remington bolt face.
What is the maximum pressure for the .204 Ruger?
The SAAMI maximum average pressure is 58,500 psi.
How do .204 Ruger and .223 Remington dimensions compare?
They share the same overall length (2.260 in) and rim size, but the .204 Ruger features a longer 1.850 inch case and a narrower 0.204 inch bullet, allowing it to achieve significantly higher velocities.