The .308 Winchester is a highly popular, bottlenecked centerfire rifle cartridge featuring a standard maximum bullet diameter of .308 inches (7.82 mm). The maximum case length is 2.015 inches (51.18 mm), and the maximum overall cartridge length (OAL) is specified at 2.810 inches (71.37 mm) to ensure compatibility with standard short action rifle magazines. The case utilizes a rim diameter of .473 inches (12.01 mm) and a base diameter of .470 inches (11.94 mm). Ammunition for this caliber is most commonly found in 150 grain, 168 grain, and 175 grain bullet weights. Exact dimensions and pressures can vary slightly depending on manufacturing tolerances and whether you reference SAAMI specifications or European C.I.P. standards.
.308 Winchester Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | .308 in (7.82 mm) | SAAMI / C.I.P. | Standard for .30 caliber projectiles. |
| 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 | .473 in (12.01 mm) | SAAMI | Standard short action bolt face dimension. |
| Case Diameter | .470 in (11.94 mm) | SAAMI | Maximum diameter measured at the base. |
| Shoulder Diameter | .454 in (11.53 mm) | SAAMI | Features a 20 degree shoulder angle. |
| Neck Diameter | .343 in (8.71 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | .470 in (11.94 mm) | SAAMI | Measured just above the extractor groove. |
| Case Capacity | 53.0 to 56.0 gr H2O | Industry Standard | Varies based on brass manufacturer and wall thickness. |
| 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 .308 inches. This dimension ensures the projectile seals properly within the barrel’s rifling to trap expanding gases and generate high velocity.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 2.015 inches. If the case is too long, it can pinch the bullet in the chamber throat and cause dangerous pressure spikes.
- 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 fit into a short action magazine and feed properly through the firearm’s action.
- Rim Diameter: The diameter of the flange at the very bottom of the case (.473 inches). The firearm’s extractor hooks onto this rim to pull the spent casing out of the chamber. This .473 inch rim is the standard for almost all short action and long action non magnum cartridges.
- Case Diameter: The width of the cartridge body. The .308 Winchester has a base diameter of .470 inches and tapers slightly to a .454 inch shoulder.
- Base Diameter: The width of the brass just above the extractor groove. It must withstand the initial expansion of ignition during firing.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging 53 to 56 grains of water, it dictates how much gunpowder the case can safely hold.
- Maximum Pressure: The peak internal pressure generated when the cartridge is fired. Standard SAAMI limits set this at 62,000 psi for the .308 Winchester.
.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 | .308 in | 7.82 mm |
| Case Length | 2.015 in | 51.18 mm |
| Overall Length | 2.810 in | 71.37 mm |
| Rim Diameter | .473 in | 12.01 mm |
| Base Diameter | .470 in | 11.94 mm |
| Shoulder Diameter | .454 in | 11.53 mm |
| Neck Diameter | .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 .470 inches, and the rim diameter is slightly larger at .473 inches.
Because the .308 Winchester operates at a high pressure of 62,000 psi, the brass case walls are subjected to extreme expansion stresses. This results in an internal case capacity of roughly 53 to 56 grains of water. Military brass or match grade brass often features thicker internal walls, which reduces the internal capacity. Reloaders must always adjust their powder charges downward when using thicker brass to avoid pressure spikes.
.308 Winchester Bullet Diameter
The standardized maximum bullet diameter for the .308 Winchester is .308 inches (7.82 mm). This specific diameter is one of the most widely used projectile sizes in the world, giving shooters access to hundreds of different bullet profiles for target shooting, hunting, and tactical applications.
It is vital not to confuse the bullet diameter with the barrel’s internal dimensions. The standard .308 Winchester barrel features a groove diameter of .308 inches and a bore (land) diameter of .300 inches. Firing a .308 inch bullet down a .300 inch bore diameter forces the bullet to engrave tightly into the rifling, creating the necessary spin to stabilize the projectile.
.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 inside standard short action rifle magazines.
However, typical factory cartridge length varies based on the bullet profile. A classic 150 grain soft point hunting round typically measures between 2.700 and 2.750 inches. In contrast, long, high ballistic coefficient target bullets like a 175 grain hollow point boat tail are deliberately seated to the maximum 2.800 to 2.810 inch OAL to keep the bullet closer to the barrel’s rifling for enhanced accuracy.
.308 Winchester Chamber And Cartridge Dimensions
The relationship between the .308 Winchester cartridge and the firearm’s chamber is critical for functionality. The .308 Winchester cartridge headspaces on its 20 degree shoulder.
This means the angled portion of the brass casing physically stops against a matching machined angle inside the barrel’s chamber, preventing the cartridge from sliding too far forward. Proper case length and shoulder setback are mandatory. If a reloader pushes the shoulder back too far during resizing, the cartridge will sit too deeply in the chamber, resulting in excessive headspace. This can cause light primer strikes or dangerous 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 rifle cartridges. Note that while some dimensions may appear identical, these cartridges are not interchangeable unless strictly specified.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Base Diameter | Maximum Pressure | Source |
| .308 Winchester | .308 in | 2.015 in | 2.810 in | .470 in | 62,000 psi | SAAMI |
| 7.62x51mm NATO | .308 in | 2.015 in | 2.800 in | .470 in | 60,191 psi | NATO / CIP |
| .30-06 Springfield | .308 in | 2.494 in | 3.340 in | .470 in | 60,000 psi | SAAMI |
| 6.5 Creedmoor | .264 in | 1.920 in | 2.825 in | .470 in | 62,000 psi | SAAMI |
| .270 Winchester | .277 in | 2.540 in | 3.340 in | .470 in | 65,000 psi | SAAMI |
| .300 Blackout | .308 in | 1.368 in | 2.260 in | .376 in | 55,000 psi | SAAMI |
.308 Winchester vs 7.62x51mm NATO Dimensions
The .308 Winchester and the military 7.62x51mm NATO are frequently confused. While their external dimensions are essentially identical, there are important internal and chamber differences.
- Case Dimensions: Both historically utilize the exact same external dimensions, including the 2.015 inch case length and .470 inch base diameter.
- Case Wall Thickness: 7.62x51mm NATO brass is typically manufactured with thicker walls to withstand violent extraction in automatic machine guns. This thicker brass significantly reduces internal powder capacity compared to commercial .308 Winchester brass.
- Chamber Headspace: A 7.62x51mm NATO rifle chamber is often cut slightly longer in the headspace dimension to ensure reliable feeding of dirty ammunition in combat conditions.
- Pressure Specification: SAAMI commercial .308 Winchester is loaded to a maximum of 62,000 psi. NATO ammunition is typically loaded to slightly lower pressures.
Because of the longer headspace in NATO chambers and higher pressure in commercial ammunition, it is generally considered safe to fire 7.62x51mm NATO in a .308 Winchester rifle, but firing high pressure .308 Winchester ammunition in older military surplus 7.62x51mm rifles requires caution.
.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.
While the dimensional specifications for the .308 Winchester are functionally identical between the two bodies to ensure global compatibility, the way they measure and report pressure differs.
- 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 exact same cartridge at 415 MPa (approximately 60,191 psi), also using piezoelectric sensors but placed at a different location on the case.
These are not contradictory figures. They are the result of different testing methodologies and measurement conventions. Ammunition loaded to SAAMI specs is safe in C.I.P. proofed hunting rifles.
.308 Winchester Bullet Weight And Dimensions
The .308 Winchester is widely loaded in several common bullet weights, which affect how the cartridge is configured.
- 150 grain: A standard hunting weight. It features a shorter profile that fits comfortably within the 2.810 inch overall length limit, leaving maximum case capacity for gunpowder.
- 168 grain: The traditional match target weight. These bullets are longer and more aerodynamic, often seated close to the 2.810 inch maximum length.
- 175 grain: A heavy match and tactical bullet designed to stay supersonic at long ranges. To maintain the 2.810 inch maximum magazine length, these long bullets must be seated deep into the powder column.
Bullet weight does not change the standardized brass case dimensions. However, because a heavier bullet is physically longer, the manufacturer must adjust the seating depth to ensure the cartridge still fits in a short action magazine.
Why .308 Winchester Dimensions Matter
Understanding the specific .308 Winchester measurements is essential for several practical reasons.
- Short Action Compatibility: The 2.810 inch overall length defines what the firearms industry calls a “short action” rifle. This allows rifles chambered in .308 to be lighter and cycle faster than “long action” rifles built for the .30-06 Springfield.
- Headspacing: Because the round headspaces on the 20 degree shoulder, cases that stretch beyond 2.015 inches must be trimmed. Failing to trim cases can prevent the bolt from closing or cause dangerous pressure spikes.
- Brass Sourcing: Because the .308 Winchester parent case spawned a massive family of cartridges (like the .243 Winchester, 7mm-08, and .338 Federal), handloaders must carefully measure neck diameters to ensure they do not accidentally mix up resized brass.
Manufacturer Specifications vs Independent Measurements
If you use calipers to measure factory .308 Winchester ammunition from companies like Federal, Winchester, or Hornady, the numbers will rarely match the SAAMI specifications exactly.
SAAMI and C.I.P. publish maximum allowable dimensions to ensure absolute safety. Ammunition manufacturers purposefully produce their cases slightly smaller than these maximums. For example, measuring a factory cartridge and finding a case length of 2.000 inches or an OAL of 2.780 inches does not mean the ammunition is defective. It simply means the manufacturer built in a reliable negative tolerance margin to guarantee that the ammunition will chamber reliably in tight or dirty rifle chambers.
Common Questions
What are the dimensions of the .308 Winchester?
The key maximum dimensions are a bullet diameter of .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).
What is the .308 Winchester bullet diameter?
The standard bullet diameter is .308 inches.
What is the .308 Winchester rim diameter?
The rim diameter measures .473 inches (12.01 mm).
What is the .308 Winchester case diameter?
The case diameter at the base is .470 inches, tapering slightly to a .454 inch shoulder.
What is the difference between .308 bore and bullet diameter?
The bullet diameter is .308 inches, while the barrel’s bore (land) diameter is .300 inches and the groove diameter is .308 inches, allowing the bullet to engage the rifling tightly.
How do .308 Winchester and 7.62x51mm NATO dimensions compare?
The external cartridge dimensions are essentially identical. However, NATO brass is thicker internally, and NATO rifle chambers are cut with longer headspace tolerances.
What is the maximum overall length of the .308 Winchester?
The absolute maximum allowed by SAAMI is 2.810 inches to ensure compatibility with short action rifle magazines.
What is the .308 Winchester maximum pressure?
The SAAMI maximum average pressure is 62,000 psi.