The 338 Lapua Magnum (8.6x70mm) is a specialized rimless, bottlenecked centerfire rifle cartridge featuring a maximum case length of 2.724 inches (69.20 mm) and a maximum overall cartridge length of 3.681 inches (93.50 mm). Based on official C.I.P. and SAAMI standards, the massive case features a 0.588 inch rim diameter, a 0.587 inch base diameter, a 0.544 inch shoulder diameter, and a maximum neck diameter of 0.372 inches. Developed specifically for extreme long range military sniping, the cartridge utilizes an oversized case web to safely contain massive powder charges and extreme pressures. Published specifications can vary slightly depending on whether they represent maximum material conditions, nominal dimensions, or specific manufacturer tolerances across different standardization bodies.
338 Lapua Magnum Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 2.724 | 69.20 | Maximum | SAAMI / C.I.P. | Standard trim to length is 2.714 in. |
| Rim Diameter | 0.588 | 14.93 | Maximum | SAAMI / C.I.P. | Requires a specialized oversized magnum bolt face. |
| Rim Thickness | 0.060 | 1.52 | Maximum | SAAMI / C.I.P. | Controls heavy extractor engagement. |
| Base Diameter | 0.587 | 14.91 | Maximum | SAAMI / C.I.P. | Measured just above the extractor groove. |
| Shoulder Diameter | 0.544 | 13.82 | Maximum | SAAMI / C.I.P. | Body to shoulder intersection. |
| Neck Diameter | 0.372 | 9.46 | Maximum | SAAMI / C.I.P. | Outside case neck diameter. |
| Neck Length | 0.327 | 8.31 | Nominal | Derived | Ensures adequate grip on heavy 338 caliber projectiles. |
| Shoulder Angle | 20° | N/A | Half Angle | SAAMI / C.I.P. | Promotes efficient powder ignition. |
| Overall Length | 3.681 | 93.50 | Maximum | SAAMI / C.I.P. | Requires magnum length actions and magazines. |
| Case Capacity | ~116.2 | 7.53 cm³ | Nominal (H2O) | Industry Std. | Varies by brass manufacturer and wall thickness. |
| Maximum Pressure | 65,000 | 448.16 MPa | Max Average | SAAMI (Piezo) | C.I.P. specifies 60,916 psi (420 MPa). |
Understanding The 338 Lapua Magnum Case Dimensions
To understand how the 338 Lapua Magnum interacts with a rifle chamber, bolt, and magazine, you must analyze its discrete geometric components. Each dimension is scaled up significantly compared to standard small arms cartridges to withstand extreme mechanical forces.
- Case Length: Measured from the base of the rim to the case mouth, case length determines how far the thick 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 extractor. The 0.588 inch diameter requires a massive bolt face, while the thickness affects how securely the extractor engages the heavy 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 ensures proper alignment and tension for heavy, high ballistic coefficient bullets.
- Overall Cartridge Length (OAL): The measurement from the case base to the tip of the seated bullet. At 3.681 inches, it dictates that this cartridge requires specially designed magnum length actions and oversized magazines.
- 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 to generate its massive kinetic energy.
338 Lapua Magnum Case Dimensions In Inches And Millimeters
Global standardization bodies use different base measurement systems. SAAMI specifications rely heavily on inches, whereas European C.I.P. standards utilize metric parameters.
| Dimension | Measurement (Inches) | Measurement (Millimeters) |
| Maximum Case Length | 2.724 in | 69.20 mm |
| Maximum Rim Diameter | 0.588 in | 14.93 mm |
| Maximum Base Diameter | 0.587 in | 14.91 mm |
| Maximum Shoulder Diameter | 0.544 in | 13.82 mm |
| Maximum Neck Diameter | 0.372 in | 9.46 mm |
| Maximum Overall Length | 3.681 in | 93.50 mm |
338 Lapua Magnum Case Length
The published maximum case length for the 338 Lapua Magnum is 2.724 inches (69.20 mm). This length provides the necessary internal volume to propel massive 250 grain and 300 grain projectiles at extreme velocities.
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. Operating at the absolute maximum length can cause the case mouth to pinch inside the chamber throat, resulting in dangerous pressure spikes. Therefore, handloaders universally utilize a trim length of 2.714 inches. This nominal case length provides a 0.010 inch buffer to ensure consistent chamber fit and safe bullet release.
338 Lapua Magnum Base And Rim Dimensions
The 338 Lapua Magnum features a beltless, rimless, bottleneck design. Its base diameter measures a massive 0.587 inches, while the rim diameter is slightly wider at 0.588 inches.
This 0.588 inch rim diameter requires a specialized oversized magnum bolt face. Unlike traditional belted magnums that headspace on a brass belt, the 338 Lapua Magnum is completely beltless and headspaces on the shoulder. This beltless design allows for a stronger case web, which is essential for containing the 65,000 psi operating pressures generated by this military grade cartridge.
338 Lapua Magnum Shoulder And Neck Dimensions
Above the straight taper of the body, the case steps down to grip a 0.338 caliber bullet. The shoulder diameter at the intersection of the case body is 0.544 inches. From there, the brass angles inward at a 20 degree half angle to meet the neck.
The neck diameter reaches a maximum allowable SAAMI specification of 0.372 inches. To safely release a 0.338 inch bullet, the chamber neck must be slightly wider than the cartridge neck. A loaded cartridge typically measures slightly below the maximum neck diameter depending on the brass wall thickness.
338 Lapua Magnum Case Capacity
Case capacity heavily influences internal ballistics, powder selection, and pressure generation. The nominal, industry accepted capacity for the 338 Lapua Magnum is approximately 116.2 grains of water, or roughly 7.53 cubic centimeters.
This immense powder capacity requires the use of extremely slow burning rifle powders. Case capacity is not a static specification. It fluctuates between brass manufacturers. Premium brass manufacturers like Lapua utilize thicker web structures near the case head for durability, which slightly reduces the internal volume compared to other commercial brands.
338 Lapua Magnum Case Dimensions vs 338 Norma Magnum
The 338 Lapua Magnum and the 338 Norma Magnum are fierce competitors in the military sniper and extreme long range shooting communities.
| Dimension | 338 Lapua Magnum | 338 Norma Magnum | Source |
| Case Length | 2.724 in | 2.492 in | SAAMI / C.I.P. |
| Rim Diameter | 0.588 in | 0.585 in | SAAMI / C.I.P. |
| Base Diameter | 0.587 in | 0.585 in | SAAMI / C.I.P. |
| Shoulder Diameter | 0.544 in | 0.564 in | SAAMI / C.I.P. |
| Neck Diameter | 0.372 in | 0.366 in | SAAMI / C.I.P. |
| Overall Length | 3.681 in | 3.681 in | SAAMI / C.I.P. |
While both cartridges share the exact same 3.681 inch overall length limit, their cases are fundamentally different.The 338 Lapua Magnum uses a long 2.724 inch case with significant body taper, dropping from a 0.587 inch base to a 0.544 inch shoulder.The 338 Norma Magnum uses a significantly shorter 2.492 inch case with much less body taper, maintaining a wider 0.564 inch shoulder.The shorter case of the Norma Magnum allows incredibly long, high ballistic coefficient bullets to be seated further out of the powder column without exceeding the 3.681 inch magazine length restriction.
338 Lapua Magnum vs 300 Winchester Magnum Case Dimensions
The 338 Lapua Magnum is substantially larger than traditional magnum hunting cartridges like the 300 Winchester Magnum.
The 300 Winchester Magnum utilizes a traditional belted case measuring 2.620 inches long with a 0.532 inch belt and a 0.513 inch base diameter. The 338 Lapua Magnum utilizes a much wider 0.587 inch beltless base and a longer 2.724 inch case. The overall length of the 300 Winchester Magnum is 3.340 inches, meaning it fits in standard long action rifles. The 338 Lapua Magnum is 3.681 inches long and requires a specialized oversized magnum action.
338 Lapua Magnum vs 50 BMG Case Dimensions
While the 338 Lapua Magnum is a massive anti-personnel sniper cartridge, it is still dwarfed by the anti-materiel 50 BMG.
The 50 BMG utilizes a colossal 0.804 inch base diameter and a 3.910 inch case length. The 338 Lapua Magnum holds less than half the powder capacity of the 50 BMG and fires a projectile that is less than half the weight.
338 Lapua Magnum Chamber And Case Dimensions
A rifle chamber must be fractionally larger than the cartridge it accepts. The relationship between 338 Lapua Magnum case dimensions and chamber dimensions centers heavily on headspacing and pressure containment.
Headspace for the 338 Lapua Magnum is measured from the bolt face to a specific datum line on the 20 degree case shoulder. When the firing pin strikes, the massive case expands to seal the chamber. Because this cartridge operates at 65,000 psi and pushes extremely heavy bullets, chamber dimensions must perfectly support the 0.587 inch case web to prevent catastrophic brass failure.
338 Lapua Magnum Case Forming And Resizing
The 338 Lapua Magnum case architecture was originally derived from the classic 416 Rigby parent case. However, modern 338 Lapua Magnum brass is completely proprietary.
A handloader cannot safely form 338 Lapua Magnum cases from 416 Rigby brass because the modern 338 Lapua Magnum requires a significantly thicker and stronger case web to safely contain 65,000 psi operating pressures. The original 416 Rigby cases were designed for much lower pressures and will rupture if loaded to modern 338 Lapua Magnum specifications. Handloaders must strictly use dedicated 338 Lapua Magnum brass.
338 Lapua Magnum Manufacturer Specifications vs Actual Measurements
There is a documented difference between absolute SAAMI standards and the dimensions of a physical cartridge sitting on a reloading bench.
SAAMI lists 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. A fired 338 Lapua Magnum 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.
Common Questions
What are the 338 Lapua Magnum case dimensions?
The key maximum case dimensions for the 338 Lapua Magnum include a 2.724 inch case length, a 0.588 inch rim diameter, a 0.587 inch base diameter, a 0.544 inch shoulder diameter, and a 0.372 inch neck diameter.
What is the 338 Lapua Magnum case length?
The maximum SAAMI and C.I.P. case length for the 338 Lapua Magnum is 2.724 inches (69.20 mm). The standard trim to length for reloading is 2.714 inches.
What is the 338 Lapua Magnum rim diameter?
The 338 Lapua Magnum rim diameter is 0.588 inches (14.93 mm max), requiring a specialized oversized magnum bolt face.
What is the 338 Lapua Magnum base diameter?
The base diameter of the 338 Lapua Magnum, measured just above the extractor groove, is 0.587 inches (14.91 mm max).
What is the 338 Lapua Magnum shoulder diameter?
The maximum shoulder diameter of the 338 Lapua Magnum is 0.544 inches (13.82 mm).
What is the 338 Lapua Magnum neck diameter?
The maximum outside neck diameter of the 338 Lapua Magnum is 0.372 inches (9.46 mm).
What is the 338 Lapua Magnum case capacity?
The nominal case capacity of the 338 Lapua Magnum is approximately 116.2 grains of water (H2O), or 7.53 cubic centimeters.
What is the 338 Lapua Magnum overall length?
The maximum overall cartridge length for the 338 Lapua Magnum is 3.681 inches (93.50 mm) under C.I.P. and SAAMI specifications.
How does 338 Lapua Magnum compare with 338 Norma Magnum case dimensions?
Both cartridges share the exact same 3.681 inch overall length limit.The 338 Lapua Magnum uses a longer 2.724 inch case with more body taper.The 338 Norma Magnum uses a shorter 2.492 inch case with less body taper, allowing exceptionally long bullets to be seated further out of the powder column without restricting powder space.
What is the 338 Lapua Magnum maximum pressure?
The SAAMI maximum average pressure for the 338 Lapua Magnum is 65,000 psi (piezo method). European C.I.P. testing methods specify the maximum pressure slightly lower at 60,916 psi (420 MPa).