The .308 Winchester is a rimless, bottlenecked centerfire rifle cartridge featuring a standard maximum bullet diameter of 0.308 inches (7.82 mm). The maximum case length is 2.015 inches (51.18 mm), and the maximum overall cartridge length is restricted to 2.810 inches (71.37 mm) to ensure compatibility with standard short action magazines. The case utilizes a rim diameter of 0.473 inches (12.01 mm) and features a base diameter of 0.470 inches (11.94 mm) that tapers slightly to a 0.454 inch (11.53 mm) shoulder. Ammunition for this caliber is most commonly found in 150 grain, 168 grain, and 175 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.
.308 Winchester Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.308 in (7.82 mm) | SAAMI | Standard for .30 caliber centerfire rifles. |
| Case Length | 2.015 in (51.18 mm) | SAAMI | Maximum case length; trim to length is typically 2.005 in. |
| Overall Cartridge Length | 2.810 in (71.37 mm) | SAAMI | Maximum overall length for short action magazines. |
| Rim Diameter | 0.473 in (12.01 mm) | SAAMI | Standard short action bolt face dimension. |
| Case Diameter (Base) | 0.470 in (11.94 mm) | SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | 0.454 in (11.53 mm) | SAAMI | Features a 20 degree shoulder angle. |
| Neck Diameter | 0.343 in (8.71 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | 0.470 in (11.94 mm) | SAAMI | Uniform with the lower case body just above the rim. |
| Case Capacity | ~ 56.0 gr H2O | Industry Standard | Varies slightly based on the brass manufacturer. |
| Maximum Pressure | 62,000 psi | SAAMI | C.I.P. maximum is 415 MPa (approximately 60,191 psi). |
Understanding The .308 Winchester Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the .308 Winchester, this is specified as 0.308 inches. This standard dimension allows the cartridge to use a massive global variety of .30 caliber target and hunting projectiles.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 2.015 inches. This specific length is the defining characteristic of a modern short action rifle cartridge.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 2.810 inches. OAL directly influences whether a cartridge will feed properly from a short action box magazine.
- Rim Diameter: The diameter of the flange at the very bottom of the case measuring 0.473 inches. The firearm extractor uses this rim to reliably pull the spent casing out of the chamber.
- Case Diameter: The width of the cartridge body at the base. At 0.470 inches, the case body is nearly identical to the rim width, defining it as a rimless design.
- Shoulder Diameter: The width of the case where it begins to angle inward toward the neck (0.454 inches). The .308 Winchester utilizes a 20 degree shoulder to headspace reliably inside the chamber.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging roughly 56.0 grains of water, it offers highly efficient powder burn characteristics.
- Maximum Pressure: The peak internal pressure generated when the cartridge is fired. Standard SAAMI limits set this at 62,000 psi to ensure safe operation in modern bolt action and semi automatic rifles.
.308 Winchester Cartridge Dimensions In Inches And Millimeters
For engineers, reloaders, and international shooters, below are the primary .308 Winchester measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Max) | Millimeters (Equivalent) |
| Bullet Diameter | 0.308 in | 7.82 mm |
| Case Length | 2.015 in | 51.18 mm |
| Overall Length | 2.810 in | 71.37 mm |
| Rim Diameter | 0.473 in | 12.01 mm |
| Base Diameter | 0.470 in | 11.94 mm |
| Shoulder Diameter | 0.454 in | 11.53 mm |
| Neck Diameter | 0.343 in | 8.71 mm |
.308 Winchester Case Dimensions
The .308 Winchester is defined by a rimless, bottlenecked case. The official maximum case length is 2.015 inches (51.18 mm), with a nominal trim to length for reloaders sitting at 2.005 inches. The base diameter measures 0.470 inches, and the rim extends slightly to 0.473 inches, creating the extractor groove.
The internal case capacity is roughly 56.0 grains of water, but this varies based on the manufacturer. The brass must be manufactured strong enough to contain 62,000 psi of pressure. Reloaders must be aware that military surplus brass manufactured to 7.62x51mm NATO specifications often features thicker internal web walls to withstand machine gun extraction. This thicker brass significantly reduces internal case capacity, requiring reloaders to reduce their powder charges to avoid dangerous pressure spikes.
.308 Winchester Bullet Diameter
The standardized maximum bullet diameter for the .308 Winchester is 0.308 inches (7.82 mm).
The standard .308 Winchester barrel features a groove diameter of 0.308 inches and a bore or land diameter of 0.300 inches. Firing a 0.308 inch bullet down a 0.300 inch bore diameter forces the copper jacket to engrave tightly into the rifling. Modern rifles for this caliber typically utilize a 1 in 10 inch or 1 in 12 inch twist rate to properly stabilize bullets ranging from 150 grains up to 180 grains.
.308 Winchester Overall Length
The SAAMI maximum overall cartridge length (OAL) for the .308 Winchester is 2.810 inches (71.37 mm). This number is a hard limit designed to guarantee that the cartridge will fit perfectly inside standard short action magazines.
Typical factory cartridge length varies based on the bullet profile. A classic 150 grain hunting bullet often measures slightly below this maximum limit. However, when ammunition manufacturers or reloaders load heavy, high ballistic coefficient match bullets like 175 grain or 185 grain projectiles, the long bullets must be seated deeper into the brass case to remain under the 2.810 inch magazine restriction. Seating bullets this deeply intrudes on the internal powder space.
.308 Winchester Chamber And Cartridge Dimensions
The relationship between the .308 Winchester cartridge and the firearm chamber is engineered around the 20 degree shoulder. The .308 Winchester headspaces entirely on this 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 aligns the bullet perfectly with the bore. Proper case length and shoulder setback are mandatory during reloading. If a reloader pushes the shoulder back too far during resizing, the cartridge will sit too loosely in the chamber, resulting in excessive headspace and a high risk of case head separation upon firing.
.308 Winchester Dimensions vs Similar Cartridges
To understand the .308 Winchester size profile, it is helpful to compare it against other popular centerfire rifle cartridges.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Base Diameter | Maximum Pressure | Source |
| .308 Winchester | 0.308 in | 2.015 in | 2.810 in | 0.470 in | 62,000 psi | SAAMI |
| 7.62x51mm NATO | 0.308 in | 2.015 in | 2.800 in | 0.470 in | 60,191 psi | NATO |
| .30-06 Springfield | 0.308 in | 2.494 in | 3.340 in | 0.470 in | 60,000 psi | SAAMI |
| 6.5 Creedmoor | 0.264 in | 1.920 in | 2.825 in | 0.470 in | 62,000 psi | SAAMI |
| .300 WSM | 0.308 in | 2.100 in | 2.860 in | 0.555 in | 65,000 psi | SAAMI |
.308 Winchester vs 7.62x51mm NATO Dimensions
The .308 Winchester and the 7.62x51mm NATO share essentially identical external cartridge dimensions, but they are not the exact same cartridge in practice.
- Chamber Dimensions: The 7.62x51mm NATO rifle chamber is cut with a slightly longer headspace tolerance. This is a deliberate military design to ensure the rifle feeds and extracts reliably in fully automatic machine guns that are heavily fouled with dirt and carbon.
- Brass Thickness: Military 7.62 NATO brass is significantly thicker near the base to withstand violent extraction. Because the external dimensions are the same, this thicker brass means the NATO cartridge has less internal volume than commercial .308 Winchester brass.
- Interchangeability: It is universally considered safe to fire 7.62x51mm NATO ammunition in a .308 Winchester chamber. However, firing commercial .308 Winchester ammunition in a surplus 7.62 NATO rifle with maximum headspace can sometimes stretch the thinner commercial brass, occasionally leading to case ruptures.
.308 Winchester 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.
SAAMI lists the maximum average pressure for the .308 Winchester at 62,000 psi, measured via conformal piezoelectric transducers. C.I.P. lists the maximum pressure for the cartridge at 415 MPa, which translates to approximately 60,191 psi. These slight variations are the result of different testing methodologies and transducer placement locations. Ammunition manufactured to either specification is perfectly safe in modern firearms chambered for the cartridge.
.308 Winchester Bullet Weight And Dimensions
The .308 Winchester is heavily standardized around several primary bullet weights, which affect how the cartridge is internally configured.
- 150 grain: A shorter bullet commonly used for medium game hunting. It leaves ample internal case capacity, allowing for heavy powder charges and velocities near 2,820 feet per second.
- 168 grain: The traditional target and match standard. These longer bullets fit perfectly within the 2.810 inch overall length limit and provide excellent stability for mid range precision shooting.
- 175 grain: Extremely popular for long range shooting past 800 yards. To fit the magazine, these long bullets must be seated deeper into the powder column, which requires specific loading data to keep pressures safe.
Why .308 Winchester Dimensions Matter
Understanding the specific .308 Winchester measurements is essential for several practical reasons.
- Action Size Definition: The 2.810 inch overall length of the .308 Winchester is the dimensional benchmark that defines modern “short action” rifles. Short actions are lighter, stiffer, and offer a faster bolt throw compared to long actions.
- Parent Case Legacy: The exceptionally efficient dimensions of the .308 Winchester case made it the parent cartridge for an entire family of legendary wildcat and commercial cartridges, including the .243 Winchester, 7mm-08 Remington, and .358 Winchester.
- Case Trimming: Because it headspaces on the shoulder, cases stretch during firing and resizing. All cases must be checked against the 2.015 inch maximum length. If a case exceeds this dimension, the case mouth will pinch in the chamber throat and cause dangerous pressure spikes.
Manufacturer Specifications vs Independent Measurements
If you use calipers to measure factory .308 Winchester ammunition from companies like Federal, Hornady, 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 2.015 inches, but measuring a factory cartridge might reveal a case length of 2.005 inches. This built in negative tolerance margin guarantees that the ammunition will chamber smoothly in the field without jamming against the barrel rifling of a tight match grade chamber.
Common Questions
What are the dimensions of the .308 Winchester?
The key maximum dimensions are a bullet diameter of 0.308 inches, a case length of 2.015 inches, and an overall cartridge length of 2.810 inches.
What is the .308 Winchester case length?
The maximum SAAMI case length is 2.015 inches (51.18 mm).
What is the .308 Winchester overall length?
The maximum overall length (OAL) is 2.810 inches (71.37 mm), designed to fit standard short action magazines.
What is the .308 Winchester bullet diameter?
The SAAMI maximum bullet diameter is 0.308 inches.
What is the .308 Winchester rim diameter?
The rim diameter measures 0.473 inches, which is the standard utilized for all bolt action rifles in this class.
What is the .308 Winchester case diameter?
The case diameter at the base is 0.470 inches, tapering gently to a 0.454 inch shoulder.
What is the maximum pressure for the .308 Winchester?
The SAAMI maximum average pressure is strictly capped at 62,000 psi.
How do .308 Winchester and .30-06 Springfield dimensions compare?
Both use a 0.308 inch bullet, but the .308 Winchester uses a shorter 2.015 inch case designed for a short action rifle, while the .30-06 Springfield uses a much longer 2.494 inch case designed for a long action rifle.
Are .308 Winchester and 7.62x51mm NATO dimensions the same?
Externally, the dimensions are functionally identical. However, 7.62 NATO military brass has thicker walls resulting in less internal capacity, and NATO rifle chambers are typically cut with looser headspace tolerances.