The .204 Ruger features a maximum case length of 1.850 inches (46.99 mm), a rim diameter of 0.378 inches (9.60 mm), a base diameter of 0.376 inches (9.55 mm), a shoulder diameter of 0.356 inches (9.04 mm), a neck diameter of 0.232 inches (5.89 mm), a neck length of approximately 0.211 inches (5.36 mm), and a maximum overall cartridge length of 2.260 inches (57.40 mm). Depending on the specification system referenced, published numerical values may represent nominal design targets, maximum manufacturing boundaries, or specific MIN/MAX tolerance windows. SAAMI establishes maximum voluntary standards in North America, while C.I.P. defines maximum cartridge dimensions for European regulatory compliance. Internal case capacity and actual physical measurements often show minor variations across different brass manufacturers such as Hornady, Winchester, Remington, Nosler, and Starline. Understanding these standardized specifications ensures correct chamber headspacing, reliable firearm extraction, accurate reloading die calibration, and safe operating pressures.
204 Ruger Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 1.850 in | 46.99 mm | Maximum | SAAMI Standard | Tolerance: -0.020 in (-0.51 mm) |
| Rim Diameter | 0.378 in | 9.60 mm | Maximum | SAAMI Standard | Tolerance: -0.010 in (-0.25 mm) |
| Rim Thickness | 0.045 in | 1.14 mm | Maximum | SAAMI Standard | Tolerance: -0.010 in (-0.25 mm) |
| Base Diameter | 0.376 in | 9.55 mm | Maximum | SAAMI Standard | Tolerance: -0.008 in (-0.20 mm) |
| Shoulder Diameter | 0.356 in | 9.04 mm | Maximum | SAAMI Standard | Located at start of 30 degree shoulder angle |
| Neck Diameter | 0.232 in | 5.89 mm | Maximum | SAAMI Standard | Measured with bullet seated |
| Neck Length | 0.211 in | 5.36 mm | Nominal Reference | C.I.P. / Reference | Distance from neck-shoulder junction to mouth |
| Shoulder Angle | 30.0 degrees | 30.0 degrees | Nominal | SAAMI Standard | 60 degrees included angle |
| Overall Cartridge Length | 2.260 in | 57.40 mm | Maximum | SAAMI Standard | Nominal testing length is 2.250 in (57.15 mm) |
| Case Capacity | 32.5 gr H2O | 2.11 cm³ | Nominal Average | Hornady / Nosler | Varies by manufacturer (31.5 to 33.0 gr H2O) |
| Maximum Pressure | 62,000 PSI | 4,275 bar | Maximum Allowable | SAAMI MAP | C.I.P. Pmax is set at 4,350 bar (63,091 PSI) |
Understanding The 204 Ruger Case Dimensions
To evaluate the .204 Ruger technical design, each physical measurement must be evaluated by its engineering function inside the firearm chamber:
- Case Length: The total distance from the exterior face of the case head to the mouth. This dimension dictates proper trim length to ensure the brass does not pinch against the chamber neck taper upon firing.
- Rim Diameter: The outer boundary of the extraction rim. This matches standard bolt faces built for the .223 Remington family, facilitating universal bolt geometry across bolt-action and semi-automatic rifles.
- Rim Thickness: The vertical depth of the rim wall. This controls extractor lip engagement and ensures sufficient clearance for bolt closure.
- Base Diameter: The exterior width of the solid case body located immediately forward of the extractor groove. It governs fit inside the rear chamber portion.
- Shoulder Diameter: The case width at the transition point where the straight body wall angles inward toward the neck.
- Neck Diameter: The outer neck measurement with a bullet seated. Proper clearance between the outer neck wall and the chamber neck allows clean release of the projectile during ignition.
- Neck Length: The vertical length of straight cylindrical brass supporting the bullet shank. Sufficient neck length provides uniform bullet tension and concentric alignment.
- Shoulder Geometry: Comprises the shoulder position and its sharp 30 degree angle. This feature establishes headspace inside the chamber while optimizing internal powder combustion.
- Overall Cartridge Length: The base-to-tip length of a fully assembled round. This guarantees compatibility with magazine boxes and controls bullet jump into the rifling throat.
- Case Capacity: The volume of water held by an unprimed, fired case filled flush to the mouth. Volume directly dictates peak pressure generation and velocity potential for given powder charges.
204 Ruger Case Dimensions In Inches And Millimeters
The following reference table converts all primary SAAMI and C.I.P. case specifications into imperial and metric units.
| Dimension Description | Inches (Imperial) | Millimeters (Metric) | Type / Definition |
| Maximum Case Length | 1.850 in | 46.99 mm | Upper limit for raw brass length |
| Minimum Case Length | 1.830 in | 46.48 mm | Lower SAAMI manufacturing limit |
| Trim-To Case Length | 1.840 in | 46.74 mm | Recommended handload prep target |
| Maximum Rim Diameter | 0.378 in | 9.60 mm | Upper boundary for bolt face fit |
| Minimum Rim Diameter | 0.368 in | 9.35 mm | Lower boundary for rim machining |
| Maximum Base Diameter | 0.376 in | 9.55 mm | Max expansion zone near case head |
| Maximum Shoulder Diameter | 0.356 in | 9.04 mm | Junction point where body meets shoulder |
| Maximum Neck Diameter | 0.232 in | 5.89 mm | Exterior neck with loaded projectile |
| Bullet Diameter | 0.204 in | 5.18 mm | Standard projectile outside diameter |
| Maximum Overall Length (COAL) | 2.260 in | 57.40 mm | Maximum length for magazine feeding |
204 Ruger Case Length
The published maximum case length for the .204 Ruger is 1.850 inches (46.99 mm) under SAAMI standards, while C.I.P. documents list the maximum case length as 47.00 mm. The recommended trim-to length for handloaders is 1.840 inches (46.74 mm), establishing a 0.010 inch safety margin below the absolute maximum.
During the firing cycle, high internal pressures push the brass outward against the chamber walls and forward toward the throat. This pressure, combined with full-length resizing operations, slowly stretches the neck forward. If a case stretches beyond the 1.850 inch maximum limit, the case mouth can jam into the forward end of the chamber neck. This creates an unintentional crimp on the bullet, preventing prompt projectile release and inducing dangerous chamber pressure spikes. Maintaining case length within official specifications is essential for operational safety and mechanical consistency.
204 Ruger Base And Rim Dimensions
The .204 Ruger features a maximum rim diameter of 0.378 inches (9.60 mm) and a maximum base diameter of 0.376 inches (9.55 mm). The rim thickness measures 0.045 inches (1.14 mm) maximum.
Because these base and rim dimensions mirror those of the .223 Remington, the .204 Ruger utilizes standard bolt faces designed for .223 Remington platforms. This compatibility allows firearm manufacturers to chamber the cartridge in existing short-action bolt rifles and AR-15 magazine systems without altering bolt face geometry or extractor mechanics. Although the case shares rim and base diameters with the .223 Remington, headspacing does not occur on the rim. The .204 Ruger headspaces directly off its 30 degree shoulder, requiring precise dimensional control during resizing to prevent excessive headspace or tight bolt closure.
204 Ruger Shoulder And Neck Dimensions
The shoulder and neck geometry of the .204 Ruger represents a central feature of its high-velocity design:
- Shoulder Diameter: 0.356 inches (9.04 mm) maximum at the body-shoulder junction.
- Shoulder Angle: 30.0 degrees (60.0 degrees included angle).
- Neck Diameter: 0.232 inches (5.89 mm) maximum with a seated bullet.
- Neck Length: Approximately 0.211 inches (5.36 mm).
The steep 30 degree shoulder angle pushes powder gases efficiently into the neck during ignition, aiding rapid flame propagation and high burn efficiency. Furthermore, this aggressive shoulder angle inhibits the forward flow of brass during firing, resulting in reduced case stretch compared to shallower 23 degree shoulder designs like the .223 Remington. The 0.211 inch neck length provides adequate contact area to hold .204 caliber projectiles straight, preserving axial alignment with the bore for enhanced accuracy.
204 Ruger Case Capacity
Published and measured water capacity for .204 Ruger brass typically spans between 31.5 grains H2O and 33.0 grains H2O (2.11 cm³ to 2.14 cm³) when measured level with the case mouth on a fired case.
Internal capacity varies noticeably across different ammunition manufacturers:
- Hornady Brass: Averages approximately 32.5 to 32.8 grains H2O.
- Nosler Brass: Averages approximately 32.4 to 32.7 grains H2O.
- Winchester Brass: Tends to feature thinner wall construction, yielding higher capacity near 33.0 grains H2O.
- Remington / Federal Brass: Typically demonstrates slightly thicker case walls, resulting in internal capacity closer to 31.5 to 32.0 grains H2O.
Because internal volume directly influences peak pressure and projectile velocity, capacity figures from one brand cannot be treated as identical to another. A powder charge developed in lightweight, high-capacity brass may produce dangerous pressures if loaded into heavier, lower-capacity brass.
204 Ruger Bullet Diameter
The standardized bullet diameter for the .204 Ruger is 0.204 inches (5.18 mm). Bullet tolerances are held between 0.201 inches and 0.204 inches under SAAMI manufacturing guidelines.
It is vital to distinguish bullet diameter from barrel dimensions:
- Bullet Diameter: 0.204 inches (5.18 mm).
- Bore Diameter (Land to Land): 0.200 inches (5.08 mm).
- Groove Diameter (Groove to Groove): 0.204 inches (5.18 mm).
Common .20 caliber commercial bullets weigh 24 grains, 32 grains, 39 grains, 40 grains, and 45 grains. The lands of the rifling etch into the 0.204 inch projectile to impart spin, while the groove diameter matches the 0.204 inch projectile diameter to form an airtight gas seal.
204 Ruger Overall Cartridge Length
SAAMI specifies a maximum overall cartridge length (COAL) of 2.260 inches (57.40 mm) for the .204 Ruger, while specifying a minimum testing length of 2.150 inches (54.61 mm).
The 2.260 inch limit matches standard AR-15 magazine wells and short-action bolt magazine boxes. Loaded factory ammunition generally measures between 2.250 inches and 2.255 inches to guarantee flawless magazine cycling. Depending on the bullet profile chosen (such as flat-base hollow points versus long polymer-tipped spitzers), seating depth must be adjusted relative to the bullet ogive to maintain clearance from the chamber throat rifling while remaining within magazine constraints.
204 Ruger Dimensions vs Similar Cartridges
Comparing the .204 Ruger against structurally similar small-caliber rifle cartridges illustrates its relative size, geometry, and volume.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Rim / Base Diameter | Case Capacity | Source |
| .204 Ruger | 0.204 in (5.18 mm) | 1.850 in (46.99 mm) | 2.260 in (57.40 mm) | 0.378 in / 0.376 in | ~32.5 gr H2O | SAAMI |
| .223 Remington | 0.224 in (5.69 mm) | 1.760 in (44.70 mm) | 2.260 in (57.40 mm) | 0.378 in / 0.376 in | ~31.4 gr H2O | SAAMI |
| .22-250 Remington | 0.224 in (5.69 mm) | 1.912 in (48.56 mm) | 2.350 in (59.69 mm) | 0.473 in / 0.470 in | ~44.5 gr H2O | SAAMI |
| .17 Remington | 0.172 in (4.37 mm) | 1.796 in (45.62 mm) | 2.170 in (55.12 mm) | 0.378 in / 0.376 in | ~27.5 gr H2O | SAAMI |
| .17 Rem Fireball | 0.172 in (4.37 mm) | 1.420 in (36.07 mm) | 1.830 in (46.48 mm) | 0.378 in / 0.376 in | ~20.5 gr H2O | SAAMI |
| .222 Remington | 0.224 in (5.69 mm) | 1.700 in (43.18 mm) | 2.130 in (54.10 mm) | 0.378 in / 0.376 in | ~27.0 gr H2O | SAAMI |
| .223 WSSM | 0.224 in (5.69 mm) | 1.670 in (42.42 mm) | 2.360 in (59.94 mm) | 0.535 in / 0.555 in | ~54.0 gr H2O | SAAMI |
Dimensional similarities do not indicate interchangeable ammunition. Each cartridge requires its specific dedicated chamber.
204 Ruger vs 223 Remington Case Dimensions
Although the .204 Ruger and .223 Remington share identical rim (0.378 in) and base (0.376 in) diameters, their primary case geometries differ substantially:
- Parent Design: The .204 Ruger is derived from the .222 Remington Magnum case, making its body longer than the .223 Remington, which derives from the standard .222 Remington.
- Case Length: The .204 Ruger case length is 1.850 inches (46.99 mm), compared to 1.760 inches (44.70 mm) for the .223 Remington.
- Shoulder Angle: The .204 Ruger utilizes a sharp 30 degree shoulder angle, whereas the .223 Remington uses a shallower 23 degree shoulder angle.
- Neck Diameter: The .204 Ruger neck diameter is 0.232 inches holding a 0.204 inch projectile, compared to 0.253 inches holding a 0.224 inch projectile on the .223 Remington.
- Case Capacity: The longer body and sharp shoulder give the .204 Ruger roughly 32.5 grains H2O capacity versus roughly 31.4 grains H2O for the .223 Remington.
204 Ruger vs 22-250 Remington Case Dimensions
The .204 Ruger and .22-250 Remington represent two distinct classes of high-velocity varmint cartridges:
- Rim and Base Size: The .22-250 Remington features a standard .308-class bolt face with a 0.473 inch rim diameter and 0.470 inch base diameter. The .204 Ruger uses a smaller .223-class bolt face with a 0.378 inch rim diameter and 0.376 inch base diameter.
- Case Length: The .22-250 Remington case length is 1.912 inches (48.56 mm), exceeding the 1.850 inch (46.99 mm) length of the .204 Ruger.
- Body Taper: The .22-250 Remington case features significant body taper, while the .204 Ruger has a straighter body design terminating in a 30 degree shoulder.
- Case Capacity: The larger body of the .22-250 Remington holds approximately 44.5 grains H2O, offering significantly more volume than the .204 Ruger’s 32.5 grains H2O.
204 Ruger vs 17 Remington Case Dimensions
Comparing the .204 Ruger to the .17 Remington shows distinct structural variations despite both targeting high-velocity pest control:
- Parent Case Base: The .17 Remington is built on the .223 Remington parent case, whereas the .204 Ruger utilizes the longer .222 Remington Magnum as its foundation.
- Case Length: The .204 Ruger length (1.850 in / 46.99 mm) is noticeably longer than the .17 Remington (1.796 in / 45.62 mm).
- Bullet and Neck Sizes: The .17 Remington holds a 0.172 inch projectile with a neck diameter of 0.199 inches, whereas the .204 Ruger holds a 0.204 inch projectile with a neck diameter of 0.232 inches.
- Shoulder Geometry: The .17 Remington features a 23 degree shoulder, while the .204 Ruger features a 30 degree shoulder.
- Capacity: The .204 Ruger provides approximately 32.5 grains H2O volume compared to roughly 27.5 grains H2O for the .17 Remington.
204 Ruger Chamber And Case Dimensions
Chamber geometry is engineered slightly larger than maximum cartridge dimensions to allow reliable mechanical feeding and extraction under operational conditions.
SAAMI chamber specifications establish these spatial relationships:
- Headspace Control: Headspace is measured from the bolt face to a designated datum point on the 30 degree chamber shoulder. For the .204 Ruger, SAAMI sets the datum diameter at 0.330 inches.
- Chamber Neck: The chamber neck diameter is cut to a minimum of 0.235 inches, providing at least 0.003 inches of radial expansion room around a maximum 0.232 inch loaded case neck. This prevents the brass neck from binding upon ignition.
- Chamber Length: Standard chamber length is cut slightly beyond the maximum 1.850 inch brass limit (typically 1.860 inches minimum) to prevent brass pinching at the throat entrance.
- Body Fit: The chamber body is machined roughly 0.002 to 0.004 inches wider than max brass dimensions to facilitate smooth feeding and extraction in repeating actions.
204 Ruger Case Forming And Resizing
The dimensional origin of the .204 Ruger stems from the .222 Remington Magnum parent case. During its commercial development by Hornady and Ruger in 2004, engineers modified the parent dimensional profile by pushing the shoulder forward, steepening the shoulder angle to 30 degrees, and necking the case mouth down from .224 caliber to .204 caliber.
Understanding these dimensional relationships helps clarify how full-length resizing dies operate. When full-length resizing .204 Ruger brass, die setup must precisely push the shoulder back to match factory headspace limits without over-working the brass, ensuring proper fire-forming longevity and preventing case head separation.
204 Ruger Manufacturer Specifications vs Actual Measurements
Discrepancies often arise when comparing official standard drawings, factory ammunition, and handloader bench measurements:
- SAAMI Standards: Define voluntary maximum cartridge and minimum chamber tolerances for North American manufacturers. These drawings reflect safety maximums rather than absolute operational targets for unfired factory rounds.
- C.I.P. Specifications: Establish mandatory legal dimensions for European proof houses. C.I.P. lists maximum case length at 47.00 mm and sets maximum allowable pressure (Pmax) at 4,350 bar (piezoelectric measurement).
- Factory Ammunition: Loaded factory rounds from Hornady, Federal, or Winchester are deliberately manufactured slightly below maximum SAAMI drawings (often 0.002 to 0.005 inches smaller) to ensure seamless feeding across all production rifles.
- Fired Brass: Once fired, the brass expands to adopt the exact dimensions of the rifle’s individual chamber, causing fired case dimensions to exceed unfired factory values.
- Resized Brass: Brass processed through sizing dies returns close to original SAAMI minimum dimensions, though metal spring-back causes slight variance depending on brass hardness and alloy composition.
Official specification drawings from SAAMI and C.I.P. remain the primary reference points for technical dimensions.
Common Questions
What are the 204 Ruger case dimensions?
Key maximum specifications under SAAMI drawings include a case length of 1.850 in (46.99 mm), rim diameter of 0.378 in (9.60 mm), base diameter of 0.376 in (9.55 mm), shoulder diameter of 0.356 in (9.04 mm), neck diameter of 0.232 in (5.89 mm), shoulder angle of 30 degrees, and maximum COAL of 2.260 in (57.40 mm).
What is the 204 Ruger case length?
The maximum SAAMI case length is 1.850 inches (46.99 mm), while C.I.P. lists 47.00 mm. Minimum SAAMI length is 1.830 inches (46.48 mm), and the standard handloader trim-to target is 1.840 inches (46.74 mm).
What is the 204 Ruger rim diameter?
The maximum rim diameter is 0.378 inches (9.60 mm) with a tolerance of -0.010 inches (-0.25 mm), matching standard .223 Remington bolt faces.
What is the 204 Ruger base diameter?
The maximum base diameter measured forward of the extractor groove is 0.376 inches (9.55 mm).
What is the 204 Ruger shoulder diameter?
The maximum shoulder diameter at the body-shoulder junction is 0.356 inches (9.04 mm), transitioning into a 30 degree shoulder angle.
What is the 204 Ruger neck diameter?
The maximum neck diameter of a loaded round is 0.232 inches (5.89 mm).
What is the 204 Ruger case capacity?
The nominal water capacity averages 32.5 grains H2O (2.11 cm³), generally spanning from 31.5 to 33.0 grains H2O depending on brass wall thickness between manufacturers.
What is the 204 Ruger overall cartridge length?
Maximum overall cartridge length (COAL) is 2.260 inches (57.40 mm) to ensure compatibility with standard AR-15 and short-action magazines.
How does 204 Ruger compare with 223 Remington case dimensions?
The .204 Ruger shares the same rim (0.378 in) and base (0.376 in) diameters as the .223 Remington, but features a longer overall case (1.850 in vs 1.760 in), a sharper shoulder angle (30 degrees vs 23 degrees), a smaller neck (.232 in vs .253 in), and a smaller bullet diameter (.204 in vs .224 in).
How does 204 Ruger compare with 22-250 Remington case dimensions?
The .22-250 Remington is a significantly larger cartridge featuring a 0.473 inch rim diameter, 0.470 inch base diameter, 1.912 inch case length, and ~44.5 grains H2O capacity compared to the .204 Ruger’s 0.378 inch rim, 0.376 inch base, 1.850 inch case length, and ~32.5 grains H2O capacity.
How does 204 Ruger compare with 17 Remington case dimensions?
The .204 Ruger features a longer case length (1.850 in vs 1.796 in), a larger bullet diameter (.204 in vs .172 in), a steeper shoulder angle (30 degrees vs 23 degrees), and higher water capacity (~32.5 gr H2O vs ~27.5 gr H2O) than the .17 Remington.
What is the 204 Ruger maximum pressure?
The maximum average pressure (MAP) established by SAAMI is 62,000 PSI. C.I.P. regulates maximum pressure (Pmax) at 4,350 bar (63,091 PSI).