The .308 Winchester is a standardized short-action centerfire rifle cartridge featuring a maximum case length of 2.015 inches (51.18 mm) and an overall cartridge length of 2.810 inches (71.37 mm). Based on official SAAMI and C.I.P. standards, the case features a 0.473-inch rim diameter, a 0.470-inch base diameter, a 0.454-inch shoulder diameter, and a 0.343-inch neck diameter. A fully formed neck spans approximately 0.303 inches. Published specifications can vary slightly depending on whether they represent maximum material conditions (MMC), nominal dimensions, or specific manufacturer tolerances across different standardization bodies.
.308 Winchester Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 2.015 | 51.18 | Maximum | SAAMI / C.I.P. | Standard trim-to length is 2.005 in. |
| Rim Diameter | 0.473 | 12.01 | Maximum | SAAMI / C.I.P. | SAAMI spec is 0.473 in (-.010); C.I.P. is 12.01 mm. |
| Rim Thickness | 0.054 | 1.37 | Maximum | SAAMI / C.I.P. | Controls bolt-face engagement. |
| Base Diameter | 0.4703 | 11.96 | Maximum | SAAMI / C.I.P. | Measured just above the extractor groove. C.I.P. rounds to 0.4709 in. |
| Shoulder Diameter | 0.4540 | 11.53 | Basic / Max | SAAMI / C.I.P. | Body-to-shoulder intersection. |
| Neck Diameter | 0.3435 | 8.72 | Maximum | SAAMI / C.I.P. | Outside case neck diameter. |
| Neck Length | 0.303 | 7.71 | Derived Nominal | SAAMI | Calculated from case length minus shoulder datum. |
| Shoulder Angle | 20° | – | Half-Angle | SAAMI | C.I.P. specifies this as a 40° included angle. |
| Overall Cartridge Length | 2.810 | 71.37 | Maximum | SAAMI | C.I.P. lists maximum overall length as 2.800 in (71.12 mm). |
| Case Capacity | ~56.0 | 3.64 cm³ | Nominal (H2O) | Industry Std. | Varies by brass manufacturer and wall thickness. |
| Maximum Pressure | 62,000 | 427.47 MPa | Max Average | SAAMI (Piezo) | C.I.P. specifies 60,191 psi (415 MPa). |
Understanding The .308 Winchester Case Dimensions
To understand how the .308 Winchester interacts with a rifle’s chamber, bolt, and magazine, you must analyze its discrete geometric components. Each dimension serves a specific engineering purpose.
- Case Length: Measured from the base of the rim to the case mouth, case length determines how far the brass extends into the chamber before contacting the end of the neck clearance.
- Rim Diameter and Thickness: The rim provides the gripping surface for the rifle’s extractor. The diameter ensures the cartridge centers on a standard short-action bolt face, while the thickness affects how securely the extractor engages the brass.
- Base Diameter: This is the widest part of the main cartridge body, situated just ahead of the extractor groove. It governs how the cartridge seats into the rear of the chamber.
- Shoulder Diameter and Geometry: The shoulder acts as the physical stop that prevents the cartridge from pushing too far into the barrel. Its diameter and 20-degree angle dictate chamber fit and headspacing.
- Neck Diameter and Length: The neck holds the bullet. The outside diameter must clear the chamber walls to allow the brass to expand and release the projectile safely upon firing. The neck length determines the amount of bearing surface available for bullet tension.
- Overall Cartridge Length (OAL): The measurement from the case base to the tip of the seated bullet. It dictates magazine fit and whether the bullet will prematurely engage the rifling lands.
- Case Capacity: The internal volume of the case, generally expressed in grains of water (gr H2O). This dictates the maximum powder charge the cartridge can safely hold.
.308 Winchester Case Dimensions In Inches And Millimeters
Global standardization bodies use different base measurement systems. SAAMI specifications rely on inches, whereas European C.I.P. standards utilize metric parameters.
| Dimension | Measurement (Inches) | Measurement (Millimeters) |
| Maximum Case Length | 2.015 in | 51.18 mm |
| Maximum Rim Diameter | 0.473 in | 12.01 mm |
| Maximum Base Diameter | 0.470 in | 11.96 mm |
| Shoulder Diameter | 0.454 in | 11.53 mm |
| Maximum Neck Diameter | 0.343 in | 8.72 mm |
| Maximum Overall Length | 2.810 in | 71.37 mm |
.308 Winchester Case Length
The published maximum case length for the .308 Winchester is 2.015 inches (51.18 mm). However, operating precisely at this maximum can cause safety issues if the case stretches during firing and pinches inside the chamber throat, spiking pressures.
Because brass flows forward under the extreme pressures of firing and resizing, a fired and full-length resized case will frequently measure longer than a factory-new case. Therefore, handloaders universally utilize a “trim-to” length of 2.005 inches. This nominal case length provides a 0.010-inch buffer, ensuring consistent chamber fit, uniform crimping, and safe bullet release.
.308 Winchester Base And Rim Dimensions
The .308 Winchester features a rimless, bottleneck design. Its base diameter measures 0.4703 inches (SAAMI) to 0.4709 inches (C.I.P.), while the rim diameter is slightly wider at 0.473 inches.
This 0.473-inch rim diameter is a foundational standard in modern firearms, inherited from the .30-06 Springfield and the earlier 7x57mm Mauser. It dictates the dimensions of the standard “short-action bolt face.” The rim thickness (0.054 inches) determines how well the bolt’s extractor claw can grip the cartridge during the violent rearward motion of cycling the action.
.308 Winchester Shoulder And Neck Dimensions
Above the straight taper of the body, the case steps down to grip the .308-caliber bullet. The shoulder diameter at the intersection of the case body is 0.454 inches. From there, the brass angles inward at a 20-degree half-angle (SAAMI) to meet the neck.
The neck diameter reaches a maximum allowable specification of 0.3435 inches (SAAMI). To safely release a 0.308-inch bullet, the chamber neck must be slightly wider than the cartridge neck. A reliable neck length of approximately 0.303 inches ensures there is enough brass-to-bullet contact to hold the projectile securely in alignment during feeding, resisting setback when the cartridge slams into the feed ramp.
.308 Winchester Case Capacity
Case capacity heavily influences internal ballistics and pressure generation. The nominal, industry-accepted capacity for the .308 Winchester is 56.0 grains of water (H2O), or roughly 3.64 cubic centimeters.
However, case capacity is not a static specification. It is a physical measurement that fluctuates between brass manufacturers. Because external dimensions are strictly controlled by chamber sizes, any variation in the thickness of the brass walls directly alters the internal volume. Brands known for heavy-duty brass (such as Lapua) often feature thicker web structures, which reduces case capacity. A reduction in case capacity causes standard powder charges to produce higher pressures, which is why load data must be adjusted when switching brass brands.
.308 Winchester Case Dimensions vs 7.62 NATO
| Dimension | .308 Winchester | 7.62×51 NATO | Source |
| Case Length | 2.015 in | 2.015 in | SAAMI / NATO STANAG |
| Rim Diameter | 0.473 in | 0.473 in | SAAMI / NATO STANAG |
| Base Diameter | 0.470 in | 0.470 in | SAAMI / NATO STANAG |
| Shoulder Diameter | 0.454 in | 0.454 in | SAAMI / NATO STANAG |
| Neck Diameter | 0.343 in | 0.343 in | SAAMI / NATO STANAG |
| Overall Cartridge Length | 2.810 in | 2.750 in (typical max) | SAAMI / NATO STANAG |
| Case Capacity | ~56.0 gr H2O | ~52.0 to 54.0 gr H2O | Standard Empirical Data |
The .308 Winchester and 7.62×51 NATO share identical external cartridge case dimensions. However, their ammunition specifications differ internally. Military 7.62×51 NATO cases are manufactured with thicker walls to survive extraction in violent machine-gun mechanisms and oversized military chambers. Consequently, 7.62 NATO brass holds less powder than commercial .308 Winchester brass.
.308 Winchester Case Dimensions vs Similar Cartridges
The .308 Winchester is the parent case for an entire family of highly successful cartridges. By necking the case up or down, manufacturers have created varying ballistic profiles using the same base cartridge architecture.
| Cartridge | Case Length | Base Diameter | Shoulder Angle | Neck Diameter | Overall Length |
| .308 Winchester | 2.015 in | 0.470 in | 20° | 0.343 in | 2.810 in |
| .30-06 Springfield | 2.494 in | 0.471 in | 17.5° | 0.340 in | 3.340 in |
| 6.5 Creedmoor | 1.920 in | 0.470 in | 30° | 0.295 in | 2.825 in |
| 7mm-08 Remington | 2.035 in | 0.470 in | 20° | 0.315 in | 2.800 in |
| .243 Winchester | 2.045 in | 0.471 in | 20° | 0.276 in | 2.710 in |
| .260 Remington | 2.035 in | 0.470 in | 20° | 0.297 in | 2.800 in |
.308 Winchester vs 7.62×51 Case Dimensions
While the exterior dimensions of the unfired brass (case length, rim diameter, base diameter, and shoulder geometry) are identical between the .308 Winchester and 7.62x51mm NATO, they are not completely interchangeable due to chamber and pressure differences.
NATO specifications allow for significantly longer headspace tolerances in the chamber to ensure reliable feeding of dirty weapons under combat conditions. Firing a higher-pressure commercial .308 Winchester round inside a generous 7.62 NATO chamber can cause the thinner commercial brass to stretch excessively, potentially leading to a case-head separation.
.308 Winchester vs 7mm-08 Case Dimensions
The 7mm-08 Remington is a direct descendant of the .308 Winchester, necked down to accept a 7mm (.284 caliber) bullet.
- Similarities: They share the same 0.470-inch base diameter, 0.473-inch rim diameter, and 20-degree shoulder angle.
- Differences: The 7mm-08 features a narrower neck diameter (0.315 inches compared to 0.343 inches) and a slightly longer case length of 2.035 inches, compared to the .308’s 2.015 inches. This slight lengthening helps prevent the smaller 7mm-08 cartridge from being accidentally chambered in a .308 rifle.
.308 Winchester vs .243 Winchester Case Dimensions
Introduced shortly after the .308, the .243 Winchester also utilizes the .308 as its parent case.
- Shared Dimensions: Base diameter (0.471 inches), rim diameter (0.473 inches), and shoulder angle (20 degrees).
- Divergent Dimensions: To accommodate the smaller .243-caliber (6mm) projectile, the .243 Winchester has a drastically reduced neck diameter of 0.276 inches. Additionally, the .243 Winchester case is lengthened to 2.045 inches, and its overall maximum cartridge length is shorter at 2.710 inches.
.308 Winchester Chamber And Case Dimensions
A rifle’s chamber must be fractionally larger than the cartridge it accepts; otherwise, the round would not feed. The relationship between .308 Winchester case dimensions and chamber dimensions centers heavily on headspacing.
Headspace for the .308 Winchester is measured from the bolt face to a specific datum line on the 20-degree case shoulder. When the firing pin strikes, the case expands to seal the chamber (obturation). If the case dimensions are too small relative to the chamber, the brass will stretch aggressively to fill the void, thinning the material near the base. If the case dimensions are too large, the bolt will not close. Proper cartridge dimensions ensure safe alignment, efficient extraction, and reliable bullet entry into the rifling.
.308 Winchester Case Forming And Resizing
Because the .308 Winchester is the parent case for the .243 Winchester, 7mm-08 Remington, .260 Remington, .338 Federal, and .358 Winchester, its brass can theoretically be formed into any of these related cartridges through mechanical resizing.
This process involves forcing the .308 brass through a specialized sizing die that alters the neck diameter and adjusts the case taper to match the new caliber. However, because the child cartridges (.243, 7mm-08, .260) have slightly longer specified case lengths (2.035 to 2.045 inches) than the .308 Winchester (2.015 inches), brass formed from a .308 case will initially fall short of the standard case length for those calibers until it stretches from repeated firing.
.308 Winchester Manufacturer Specifications vs Actual Measurements
There is a documented difference between absolute standards (SAAMI/C.I.P.) and the dimensions of a physical cartridge sitting on a reloading bench.
- Standardized vs Factory: SAAMI and C.I.P. list Maximum Material Conditions. Ammunition manufacturers intentionally produce brass slightly smaller than these maximums to guarantee their cartridges will chamber in any rifle, regardless of how tightly the manufacturer cut the chamber.
- Fired vs Resized: A fired .308 case expands to the exact dimensions of the specific rifle chamber it was fired in. When a handloader runs this fired brass through a full-length sizing die, the machine compresses the base, shoulder, and neck back down to factory-nominal tolerances, allowing it to chamber easily once again.
- Tolerance Translation: SAAMI uses an imperial tolerance system (e.g., Base: 0.4703 inches minus 0.008 inches), whereas C.I.P. uses metric translation. When these numbers are converted back and forth, slight discrepancies appear (like 0.4703 inches vs 0.4709 inches), but they reflect measurement system variances rather than incompatible cartridges.
Common Questions
What are the .308 Winchester case dimensions?
The key maximum case dimensions for the .308 Winchester include a 2.015-inch case length, a 0.473-inch rim diameter, a 0.470-inch base diameter, a 0.454-inch shoulder diameter, and a 0.343-inch neck diameter.
What is the .308 Winchester case length?
The maximum SAAMI and C.I.P. case length for the .308 Winchester is 2.015 inches (51.18 mm). The standard trim-to length for reloading is 2.005 inches.
What is the .308 Winchester rim diameter?
The .308 Winchester rim diameter is 0.473 inches (12.01 mm max).
What is the .308 Winchester base diameter?
The base diameter of the .308 Winchester, measured just above the extractor groove, is 0.470 inches (SAAMI lists 0.4703 max, while C.I.P. lists 11.96 mm / 0.4709 inches).
What is the .308 Winchester shoulder diameter?
The maximum shoulder diameter of the .308 Winchester is 0.454 inches (11.53 mm).
What is the .308 Winchester neck diameter?
The maximum outside neck diameter of the .308 Winchester is 0.343 inches (SAAMI max is 0.3435 inches; C.I.P. is 8.72 mm / 0.3433 inches).
What is the .308 Winchester case capacity?
The nominal case capacity of the .308 Winchester is 56.0 grains of water (H2O), or 3.64 cubic centimeters. Actual capacity varies depending on the brass manufacturer’s wall thickness.
What is the .308 Winchester overall length?
The maximum overall cartridge length (OAL) for the .308 Winchester is 2.810 inches (71.37 mm) under SAAMI specifications, while C.I.P. specifies 2.800 inches (71.12 mm).
How does .308 Winchester compare with 7.62×51 case dimensions?
The exterior case dimensions of the .308 Winchester and 7.62x51mm NATO are virtually identical. However, 7.62×51 NATO military brass is thicker, reducing the internal case capacity compared to commercial .308 Winchester brass.
Are .308 Winchester and 7.62×51 case dimensions the same?
Externally, the case dimensions are the same. Internally, they differ due to thicker military brass webs. Furthermore, the chamber specifications differ, with NATO chambers allowing for significantly looser headspace tolerances.
How does .308 Winchester compare with 7mm-08 case dimensions?
While both cartridges share a 0.470-inch base and 0.473-inch rim, the 7mm-08 Remington has a narrower neck (0.315 inches) to hold a 7mm bullet, and a slightly longer case length of 2.035 inches compared to the .308’s 2.015 inches.
How does .308 Winchester compare with .243 Winchester case dimensions?
Both share the same parent case architecture, but the .243 Winchester utilizes a tightly necked-down 0.276-inch neck diameter for 6mm bullets. The .243 Winchester also has a longer maximum case length of 2.045 inches, but a shorter overall cartridge length of 2.710 inches.
What is the .308 Winchester maximum pressure?
The SAAMI maximum average pressure (MAP) for the .308 Winchester is 62,000 psi (piezo method). Under C.I.P. testing methods, the maximum pressure is rated at 60,191 psi (415 MPa).