The .308 Winchester case length is a fundamental standardized dimension critical for firearm safety, chamber fitting, and cartridge identification. Under SAAMI (Sport Arms and Ammunition Manufacturers’ Institute) standards, the maximum .308 Winchester case length is 2.015 inches (51.18 mm). While new factory brass or trimmed cases typically measure closer to a “trim-to” length of 2.005 inches (50.93 mm), brass expands upon firing and stretches during resizing, making monitoring maximum case length essential.
308 Case Length
| Measurement | Inches | Millimeters | Type |
| Maximum Case Length | 2.015 | 51.18 | SAAMI specification |
| Nominal/Reference Case Length | 2.015 | 51.18 | C.I.P. standard specification |
| Typical New Factory Case Length | 2.005 to 2.010 | 50.93 to 51.05 | Manufacturer data (typical tolerances) |
| Trim-to Length | 2.005 | 50.93 | Standard reload industry reference (SAAMI -0.010 in.) |
308 Case Length: The .308 Winchester has a maximum case length of 2.015 inches (51.18 mm) under the SAAMI specification.
How Long Is a 308 Case?
The empty brass .308 Winchester case length is exactly 2.015 inches (51.18 mm) at its maximum allowable SAAMI threshold. In metric terms, 2.015 inches translates directly to 51.18 mm.
It is vital to distinguish case length from cartridge overall length (COAL). Case length measures solely the brass hull from the base of the rim to the top of the case mouth. Cartridge overall length measures the entire complete assembly, starting from the base of the rim all the way to the tip of the seated bullet. Because the complete loaded cartridge includes the bullet protruding from the neck, its overall length is significantly longer than the empty brass case.
308 Case Length in Inches and Millimeters
| Measurement | Inches | Millimeters |
| 308 Case Length | 2.015 | 51.18 |
(Mathematical verification: 2.015 inches × 25.4 mm/inch = 51.181 mm, rounding to 51.18 mm).
308 Winchester Case Dimensions
| Case Dimension | Inches | Millimeters | Measurement Standard |
| Case Length | 2.015 | 51.18 | SAAMI Maximum |
| Rim Diameter | 0.473 | 12.01 | SAAMI Maximum |
| Rim Thickness | 0.054 | 1.37 | SAAMI Maximum |
| Base Diameter | 0.4709 | 11.96 | SAAMI Maximum |
| Shoulder Diameter | 0.4543 | 11.54 | SAAMI Maximum |
| Neck Diameter | 0.3433 | 8.72 | SAAMI Maximum (with bullet seated) |
| Shoulder Angle | 20 degrees | 20 degrees | SAAMI Reference Angle (side angle) |
308 Case Length vs 308 Overall Cartridge Length
The 308 case length measures only the empty cylindrical brass container before a projectile is added. The 308 overall cartridge length (COAL) measures the total combined distance from the brass rim base to the tip of the projectile in a fully loaded piece of ammunition.
| Measurement | .308 Winchester |
| Maximum case length | 2.015 in. (51.18 mm) |
| Maximum overall cartridge length | 2.810 in. (71.37 mm) |
Case length ensures the neck of the brass does not extend too far into the throat of the chamber, while maximum cartridge overall length ensures the loaded round feeds properly through rifle magazines and functions through the bolt action smoothly.
308 Case Length vs 7.62 NATO
While .308 Winchester and 7.62×51mm NATO share origin history, they are governed by different specification bodies (SAAMI/C.I.P. for commercial .308 Winchester and NATO STANAG 2310 for 7.62 NATO).
| Dimension | .308 Winchester (SAAMI) | 7.62×51mm NATO (STANAG) |
| Case Length (Max) | 2.015 in. (51.18 mm) | 2.015 in. (51.18 mm) |
| Overall Cartridge Length (Max) | 2.810 in. (71.37 mm) | 2.830 in. (71.88 mm) |
| Rim Diameter | 0.473 in. (12.01 mm) | 0.473 in. (12.01 mm) |
| Base Diameter | 0.4709 in. (11.96 mm) | 0.4703 in. (11.95 mm) |
| Shoulder Diameter | 0.4543 in. (11.54 mm) | 0.454 in. (11.53 mm) |
| Neck Diameter | 0.3433 in. (8.72 mm) | 0.345 in. (8.76 mm) |
Though basic case length is identical at 2.015 inches, 7.62 NATO military chambers feature longer headspace allowances and thicker military brass walls, meaning commercial .308 Winchester and military 7.62 NATO should not automatically be treated as having identical chamber pressure or dimension tolerances.
308 Case Length vs 30 06
The .308 Winchester was designed in the 1950s as a compact replacement for the longer .30-06 Springfield military cartridge.
| Dimension | .308 Winchester | .30-06 Springfield |
| Case length | 2.015 in. (51.18 mm) | 2.494 in. (63.35 mm) |
| Overall cartridge length | 2.810 in. (71.37 mm) | 3.340 in. (84.84 mm) |
| Rim diameter | 0.473 in. (12.01 mm) | 0.473 in. (12.01 mm) |
| Base diameter | 0.4709 in. (11.96 mm) | 0.4709 in. (11.96 mm) |
| Typical bullet diameter | 0.308 in. (7.82 mm) | 0.308 in. (7.82 mm) |
The .30-06 Springfield case length is nearly half an inch longer than the .308 Winchester case length (2.494 inches vs 2.015 inches). Both cartridges share the exact same rim diameter and shoot identical .308-inch diameter bullets, but the .308 Winchester achieves comparable ballistics in a much shorter, more efficient action design.
308 Case Length vs 6.5 Creedmoor
The 6.5 Creedmoor was developed by necking down a modified case concept to shoot slimmer 6.5mm projectiles while fitting in short-action rifle magazines.
| Dimension | .308 Winchester | 6.5 Creedmoor |
| Case length | 2.015 in. (51.18 mm) | 1.920 in. (48.77 mm) |
| Overall cartridge length | 2.810 in. (71.37 mm) | 2.825 in. (71.76 mm) |
| Rim diameter | 0.473 in. (12.01 mm) | 0.473 in. (12.01 mm) |
| Base diameter | 0.4709 in. (11.96 mm) | 0.4703 in. (11.95 mm) |
| Shoulder dimensions | 20-degree angle / 0.4543 in. | 30-degree angle / 0.462 in. |
The 6.5 Creedmoor features a shorter case length (1.920 inches) compared to the .308 Winchester (2.015 inches). This deliberate reduction in case length allows long, aerodynamic 6.5mm bullets to be seated far out without exceeding short-action magazine overall length limits.
308 Case Length vs 223
The .223 Remington is a small-caliber intermediate rifle round, whereas the .308 Winchester is a full-power, short-action battle and hunting cartridge.
| Dimension | .308 Winchester | .223 Remington |
| Case length | 2.015 in. (51.18 mm) | 1.760 in. (44.70 mm) |
| Overall cartridge length | 2.810 in. (71.37 mm) | 2.260 in. (57.40 mm) |
| Rim diameter | 0.473 in. (12.01 mm) | 0.378 in. (9.60 mm) |
| Base diameter | 0.4709 in. (11.96 mm) | 0.3759 in. (9.55 mm) |
| Bullet diameter | 0.308 in. (7.82 mm) | 0.224 in. (5.69 mm) |
The .308 Winchester case length is substantially larger in all physical dimensions than the .223 Remington, featuring a case length that is 0.255 inches longer and a rim diameter that is nearly 0.1 inches wider.
Why 308 Case Length Matters
Standardized .308 Winchester case dimensions serve crucial technical roles in firearm mechanics and industry manufacturing:
- Cartridge Identification: Correct dimensions prevent dangerous cross-loading of visually similar calibers into incorrect rifle chambers.
- Chamber Dimensions: Rifle barrels are reamed to precise minimum and maximum tolerances. If a brass case exceeds the maximum length of 2.015 inches, the neck can pinch against the end of the chamber forcing cone, causing dangerous spikes in peak pressure when fired.
- Ammunition Compatibility: Standardized case lengths guarantee that factory ammunition functions reliably across all rifle makes and models adhering to SAAMI or C.I.P. standards.
- Factory Ammunition Specifications: Commercial manufacturers use standardized case trim dimensions to ensure proper bullet neck tension and consistent manufacturing quality.
- Reloading Reference Information: Case length measurement provides a critical safety check point for inspectable wear, letting users know when repeatedly fired brass needs trimming back down to nominal reference dimensions.
308 Case Length FAQs
What is the case length of a 308?
The maximum SAAMI case length of a .308 Winchester is 2.015 inches (51.18 mm).
How long is a 308 Winchester case?
A standard .308 Winchester case is 2.015 inches long at maximum allowance, with typical trim targets set at 2.005 inches.
What is 308 case length in mm?
In millimeters, the maximum .308 Winchester case length is 51.18 mm.
What is the maximum 308 case length?
The maximum published SAAMI specification for .308 Winchester case length is 2.015 inches.
Is 2.015 inches the 308 case length?
Yes, 2.015 inches is the official maximum case length specification for the .308 Winchester cartridge.
What is the difference between 308 case length and overall length?
Case length measures only the empty brass shell (2.015 in. max), while overall cartridge length measures the entire round with the bullet seated inside the brass (2.810 in. max).
Is 308 the same case length as 7.62 NATO?
Yes, both .308 Winchester and 7.62×51mm NATO share an identical maximum case length specification of 2.015 inches (51.18 mm).
Is the 308 case longer than 223?
Yes, the .308 Winchester case length (2.015 in.) is longer than the .223 Remington case length (1.760 in.).
Is the 308 case shorter than 30 06?
Yes, the .308 Winchester case length (2.015 in.) is significantly shorter than the .30-06 Springfield case length (2.494 in.).
What is the 308 Winchester cartridge overall length?
The maximum SAAMI cartridge overall length (COAL) for the .308 Winchester is 2.810 inches (71.37 mm).