The .338 Lapua Magnum (also known metrically as the 8.6x70mm) is a massive rimless, bottlenecked centerfire rifle cartridge featuring a standard maximum bullet diameter of 0.338 inches (8.58 mm). The maximum case length is 2.724 inches (69.20 mm), and the maximum overall cartridge length (OAL) is specified at 3.681 inches (93.50 mm) to accommodate incredibly long, high ballistic coefficient bullets. The case utilizes an oversized magnum rim diameter of 0.588 inches (14.93 mm) and a wide base diameter of 0.587 inches (14.91 mm). Ammunition for this caliber is most commonly found in heavy 250 grain, 285 grain, and 300 grain bullet weights. Exact dimensions and operating pressures can vary slightly depending on manufacturing tolerances and whether you reference European C.I.P. standards or American SAAMI specifications.
.338 Lapua Magnum Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.338 in (8.58 mm) | C.I.P. / SAAMI | Standard for .338 caliber centerfire rifles. |
| Case Length | 2.724 in (69.20 mm) | C.I.P. / SAAMI | Maximum case length; trim to length is typically 2.714 in. |
| Overall Cartridge Length | 3.681 in (93.50 mm) | C.I.P. / SAAMI | Maximum overall length for extreme magnum rifle actions. |
| Rim Diameter | 0.588 in (14.93 mm) | C.I.P. / SAAMI | Requires a specialized oversized magnum bolt face. |
| Case Diameter (Base) | 0.587 in (14.91 mm) | C.I.P. / SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | 0.543 in (13.80 mm) | C.I.P. / SAAMI | Features a steep 20 degree shoulder angle. |
| Neck Diameter | 0.372 in (9.46 mm) | C.I.P. / SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | 0.587 in (14.91 mm) | C.I.P. / SAAMI | Beltless design derived from the .416 Rigby parent case. |
| Case Capacity | ~ 114.0 gr H2O | Industry Standard | Varies slightly based on the brass manufacturer and wall thickness. |
| Maximum Pressure | 68,000 psi | SAAMI | C.I.P. maximum is 420 MPa (approximately 60,916 psi). |
Understanding The .338 Lapua Magnum Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the .338 Lapua Magnum, this is specified as 0.338 inches. This dimension ensures the heavy projectile seals properly within the barrel rifling to trap expanding gases and generate extreme long range energy.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 2.724 inches. This massive case length provides the internal volume necessary to hold over 90 grains of slow burning gunpowder.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 3.681 inches. This extreme length dictates that the .338 Lapua Magnum requires a specialized CIP length magnum action to feed and eject properly.
- Rim Diameter: The diameter of the flange at the very bottom of the case measuring 0.588 inches. Because this is significantly wider than standard magnums (which use a 0.532 inch rim), a rifle must be built with a dedicated .338 Lapua sized bolt face.
- Case Diameter: The width of the cartridge body at the base. At 0.587 inches, the case provides a massive powder column without requiring a traditional brass belt for headspacing.
- Shoulder Diameter: The width of the case where it begins to angle inward toward the neck (0.543 inches). The cartridge utilizes a 20 degree shoulder to optimize powder burn efficiency and provide a solid surface for headspacing.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging roughly 114.0 grains of water, this cartridge holds enough powder to accurately propel heavy bullets well past one mile.
- Maximum Pressure: The peak internal pressure generated when the cartridge is fired. SAAMI limits set this at an intense 68,000 psi.
.338 Lapua Magnum Cartridge Dimensions In Inches And Millimeters
For engineers, reloaders, and international shooters, below are the primary .338 Lapua Magnum measurements converted accurately between imperial and metric systems.
| Dimension | Inches (Max) | Millimeters (Equivalent) |
| Bullet Diameter | 0.338 in | 8.58 mm |
| Case Length | 2.724 in | 69.20 mm |
| Overall Length | 3.681 in | 93.50 mm |
| Rim Diameter | 0.588 in | 14.93 mm |
| Base Diameter | 0.587 in | 14.91 mm |
| Shoulder Diameter | 0.543 in | 13.80 mm |
| Neck Diameter | 0.372 in | 9.46 mm |
.338 Lapua Magnum Case Dimensions
The .338 Lapua Magnum is defined by a massive, beltless, bottlenecked case derived directly from the classic .416 Rigby. The official maximum case length is 2.724 inches (69.20 mm), with a nominal trim to length for reloaders sitting at 2.714 inches. The base diameter measures 0.587 inches, blending smoothly into the 0.588 inch rim.
Because the .338 Lapua Magnum was developed specifically as a military sniper cartridge, the brass case web is manufactured exceptionally thick to withstand high pressures and violent extraction forces. The case walls are drawn to expand perfectly within the chamber. The 20 degree shoulder angle provides excellent headspacing control and extends the reloading life of the brass by preventing excessive forward flow of the metal during firing.
.338 Lapua Magnum Bullet Diameter
The standardized maximum bullet diameter for the .338 Lapua Magnum is 0.338 inches (8.58 mm). This caliber choice provides the perfect balance between the aerodynamic efficiency of smaller 30 caliber bullets and the massive payload capacity of 50 caliber projectiles.
The standard .338 Lapua Magnum barrel features a groove diameter of 0.338 inches and a bore or land diameter of 0.330 inches. Firing a 0.338 inch bullet down a 0.330 inch bore diameter forces the thick copper jacket to engrave tightly into the rifling. Rifles chambered in this caliber typically utilize a 1 in 10 inch twist rate to stabilize standard 250 grain bullets, while custom barrels built for ultra heavy 300 grain bullets often utilize a faster 1 in 9 inch twist rate.
.338 Lapua Magnum Overall Length
The standard maximum overall cartridge length (OAL) for the .338 Lapua Magnum is 3.681 inches (93.50 mm). This massive overall length is the defining dimensional characteristic of the cartridge and dictates the size of the rifle required to fire it.
When using standard 250 grain military style bullets, the ammunition typically fits easily within this 3.681 inch limit. However, the modern trend of using incredibly long 300 grain match bullets presents a dimensional challenge. If seated to the standard OAL, these massive bullets intrude deeply into the powder column. To avoid this, many custom rifle builders and reloaders seat 300 grain bullets out to an OAL of 3.750 inches or longer, which requires the use of specialized oversized magazines and extended chamber throats.
.338 Lapua Magnum Chamber And Cartridge Dimensions
The relationship between the .338 Lapua Magnum cartridge and the firearm chamber is engineered for absolute precision at extreme ranges. The cartridge headspaces entirely on its 20 degree 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, solid stopping point that aligns the bullet perfectly concentric to the bore. Because the cartridge operates at incredibly high pressures, chamber dimensions must be cut to strict tolerances. If a chamber has excessive headspace, the thick brass case will stretch violently upon firing, leading to case head separation and potential catastrophic failure of the rifle action.
.338 Lapua Magnum Dimensions vs Similar Cartridges
To understand the .338 Lapua Magnum size profile, it is helpful to compare it against other popular extreme long range rifle cartridges.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Base Diameter | Maximum Pressure | Source |
| .338 Lapua Mag | 0.338 in | 2.724 in | 3.681 in | 0.587 in | 68,000 psi | SAAMI |
| .338 Norma Mag | 0.338 in | 2.492 in | 3.681 in | 0.587 in | 63,816 psi | C.I.P. |
| .338 Win Mag | 0.338 in | 2.500 in | 3.340 in | 0.513 in | 64,000 psi | SAAMI |
| .300 PRC | 0.308 in | 2.580 in | 3.700 in | 0.532 in | 65,000 psi | SAAMI |
| .50 BMG | 0.510 in | 3.910 in | 5.450 in | 0.804 in | 54,000 psi | SAAMI |
.338 Lapua Magnum vs .338 Norma Magnum Dimensions
The .338 Lapua Magnum and the .338 Norma Magnum are fierce competitors in the military sniper and extreme long range shooting communities. While both utilize the exact same 0.587 inch base diameter and share the same 3.681 inch overall length limit, their cases are fundamentally different.
- Case Length: The .338 Lapua Magnum uses a long 2.724 inch case. The .338 Norma Magnum uses a significantly shorter 2.492 inch case.
- Bullet Seating: Because the .338 Norma Magnum case is shorter but shares the same 3.681 inch OAL, it allows extremely long 300 grain bullets to be seated farther forward. This keeps the base of the long bullets completely out of the powder column, whereas the longer Lapua case forces 300 grain bullets deeper into the powder space.
- Shoulder Angle: The .338 Lapua features a 20 degree shoulder, while the .338 Norma utilizes a steeper shoulder to maximize capacity in its shorter case. Both cartridges deliver nearly identical ballistic performance.
.338 Lapua Magnum 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.
The .338 Lapua Magnum was originally developed in Europe and standardized by C.I.P., which lists the maximum pressure at 420 MPa (approximately 60,916 psi). SAAMI later adopted the cartridge and set the maximum average pressure significantly higher at 68,000 psi, measured via conformal piezoelectric transducers. While the pressure limits differ due to testing methodologies and standardization timelines, the physical dimensional specifications remain identical between the two bodies to ensure global compatibility. Ammunition manufactured to either specification is safe in properly chambered modern rifles.
.338 Lapua Magnum Bullet Weight And Dimensions
The .338 Lapua Magnum was optimized entirely around the heaviest, most aerodynamic bullets available in the 338 caliber spectrum. Common factory bullet weights include:
- 250 grain: The original military standard weight (such as the Lapua Scenar). These bullets fit perfectly within the 3.681 inch overall length limit while leaving maximum case capacity for heavy powder charges, resulting in velocities near 3,000 feet per second.
- 285 grain: A modern compromise favored by long range hunters and target shooters. These bullets offer incredible ballistic coefficients while still fitting reasonably well inside standard magazines.
- 300 grain: The standard for extreme long range shooting past 1,500 yards. To maintain magazine length restrictions, these massive bullets must be seated deeply into the brass case.
Bullet weight does not alter the external brass case dimensions, but the manufacturer must carefully manage bullet seating depth to ensure the loaded round takes full advantage of the magnum length magazine.
Why .338 Lapua Magnum Dimensions Matter
Understanding the specific .338 Lapua Magnum measurements is essential for several practical reasons.
- Action Size Requirements: The 3.681 inch overall length and massive 0.587 inch base diameter mean shooters cannot simply rebarrel a standard magnum rifle (like a .300 Win Mag). The cartridge strictly requires a specialized extreme magnum length action to feed and extract reliably.
- Magazine Selection: Shooters building custom precision rifles must purchase specialized CIP length magazines to accommodate the massive overall length of the cartridge. Standard long action magazines will not physically accept the ammunition.
- Reloading Equipment: The 2.724 inch case length and massive overall size mean standard reloading presses are often too short to comfortably accommodate the cartridge. Reloaders typically require oversized presses with extended ram clearance to safely seat long bullets.
Manufacturer Specifications vs Independent Measurements
If you use precision calipers to measure factory .338 Lapua Magnum ammunition from companies like Lapua, Hornady, or Federal, the numbers will rarely match the maximum specifications exactly.
C.I.P. and SAAMI publish maximum allowable dimensions to ensure absolute safety and interoperability across all rifle builders. Ammunition manufacturers purposefully produce their cases slightly smaller than these maximums. For example, the maximum case length is 2.724 inches, but measuring a factory cartridge might reveal a case length of 2.712 inches. This built in negative tolerance margin guarantees that the massive ammunition will chamber smoothly in the field without jamming in tight match grade chambers.
Common Questions
What are the dimensions of the .338 Lapua Magnum?
The key maximum dimensions are a bullet diameter of 0.338 inches, a case length of 2.724 inches, and a massive overall cartridge length of 3.681 inches.
What is the .338 Lapua Magnum case length?
The maximum case length is 2.724 inches (69.20 mm).
What is the .338 Lapua Magnum overall length?
The maximum overall length (OAL) is 3.681 inches (93.50 mm), requiring a specialized CIP length magnum rifle action.
What is the .338 Lapua Magnum bullet diameter?
The maximum bullet diameter is 0.338 inches.
What is the .338 Lapua Magnum rim diameter?
The rim diameter measures 0.588 inches, requiring a much larger bolt face than standard belted magnums.
What is the .338 Lapua Magnum case capacity?
The .338 Lapua Magnum holds approximately 114.0 grains of water depending on the exact thickness of the specific brass casing.
What is the maximum pressure for the .338 Lapua Magnum?
The SAAMI maximum average pressure is strictly capped at 68,000 psi, while C.I.P. lists the maximum at roughly 60,916 psi (420 MPa).
How do .338 Lapua Magnum and .338 Win Mag dimensions compare?
They share the same bullet diameter of 0.338 inches, but the .338 Lapua Magnum utilizes a much longer 2.724 inch case, a massive 0.587 inch beltless base, and a longer 3.681 inch overall length compared to the smaller belted .338 Win Mag.
Does the .338 Lapua Magnum use a standard magnum bolt face?
No. Standard magnums use a 0.532 inch bolt face. The .338 Lapua Magnum requires an oversized 0.588 inch bolt face.