The 400 Legend is a straight-walled centerfire rifle cartridge featuring a standard maximum bullet diameter of 0.4005 inches (10.17 mm). The maximum case length is 1.650 inches (41.91 mm), and the maximum overall cartridge length is restricted to 2.260 inches (57.40 mm) to ensure compatibility with standard AR-15 magazine wells. The case utilizes a heavily rebated rim diameter of 0.422 inches (10.72 mm) and tapers very slightly from a wider base diameter of 0.440 inches (11.18 mm) to a case mouth diameter of 0.4267 inches (10.84 mm). Ammunition for this caliber is most commonly found in 190 grain and 215 grain bullet weights for hunting, along with heavy 300 grain subsonic options. Exact dimensions can vary slightly depending on manufacturing tolerances and allowable specifications.
400 Legend Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.4005 in (10.17 mm) | SAAMI | Standard for .40 caliber rifle projectiles. |
| Case Length | 1.650 in (41.91 mm) | SAAMI | Maximum case length; complies with 1.800 inch hunting regulations. |
| Overall Cartridge Length | 2.260 in (57.40 mm) | SAAMI | Maximum overall length for standard AR-15 style magazines. |
| Rim Diameter | 0.422 in (10.72 mm) | SAAMI | Reuses the standard 6.8 SPC bolt face dimension. |
| Case Diameter (Base) | 0.440 in (11.18 mm) | SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | N/A | N/A | Straight-walled cartridge; no shoulder. |
| Neck Diameter | 0.4267 in (10.84 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | 0.440 in (11.18 mm) | SAAMI | Wider than the rim, making it a heavily rebated rim cartridge. |
| Case Capacity | ~ 44.0 gr H2O | Industry | Varies slightly based on the brass manufacturer. |
| Maximum Pressure | 45,000 psi | SAAMI | Governed by SAAMI specifications for modern hunting rifles. |
Understanding The 400 Legend Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the 400 Legend, this is specified as a maximum of 0.4005 inches. This dimension ensures the projectile seals properly within the barrel rifling to trap expanding gases and generate hunting velocity.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 1.650 inches. This specific length allows the cartridge to be used for hunting in states that mandate straight-walled cartridges with a maximum length of 1.800 inches.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 2.260 inches. OAL directly influences whether a cartridge will fit into a standard magazine and feed properly through the firearm action.
- Rim Diameter: The diameter of the flange at the very bottom of the case measuring 0.422 inches. The firearm extractor hooks onto this rim to pull the spent casing out of the chamber. Because it matches the 6.8 SPC, the 400 Legend requires a 6.8 SPC patterned AR-15 bolt.
- Case Diameter: The width of the cartridge body at the base. At 0.440 inches, it is wider than the rim, forming what is known as a rebated rim.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging 44.0 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 45,000 psi, ensuring reliable operation without exceeding the safe limits of AR-15 bolt lugs.
400 Legend Cartridge Dimensions In Inches And Millimeters
For engineers, reloaders, and international shooters, below are the primary 400 Legend measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Max) | Millimeters (Equivalent) |
| Bullet Diameter | 0.4005 in | 10.17 mm |
| Case Length | 1.650 in | 41.91 mm |
| Overall Length | 2.260 in | 57.40 mm |
| Rim Diameter | 0.422 in | 10.72 mm |
| Base Diameter | 0.440 in | 11.18 mm |
| Neck Diameter | 0.4267 in | 10.84 mm |
400 Legend Case Dimensions
The 400 Legend is defined by a rimless, straight-walled case featuring a prominent rebated rim. The official maximum case length is 1.650 inches (41.91 mm), with a nominal trim to length for reloaders sitting at roughly 1.640 inches. The base diameter measures 0.440 inches, while the rim diameter is cut noticeably narrower at 0.422 inches.
Because the case is essentially straight-walled with minimal body taper, it offers a large internal volume for its compact size. The internal case capacity is roughly 44.0 grains of water. This capacity is highly efficient, allowing the 400 Legend to push heavy 0.40-caliber bullets at high hunting velocities using relatively small charges of fast-burning rifle powders.
400 Legend Bullet Diameter
The standardized maximum bullet diameter for the 400 Legend is 0.4005 inches (10.17 mm). While this shares a similar diameter to handgun cartridges like the 10mm Auto or .40 S&W, the 400 Legend utilizes specifically designed rifle bullets built to handle much higher velocities and offer deeper penetration on medium to large game.
The standard 400 Legend barrel features a groove diameter of 0.400 inches and a bore or land diameter of 0.390 inches. Firing a 0.4005 inch bullet down a 0.400 inch groove diameter forces the copper jacket to engrave tightly into the rifling, creating the necessary spin to stabilize the projectile accurately in flight. Most 400 Legend barrels are manufactured with a 1:16 twist rate.
400 Legend Overall Length
The SAAMI maximum overall cartridge length (OAL) for the 400 Legend is 2.260 inches (57.40 mm). This number is a hard limit designed to guarantee that the cartridge will fit perfectly inside standard AR-15 magazines without modifying the lower receiver of the firearm.
Typical factory cartridge length varies based on the bullet profile. A 190 grain or 215 grain hunting bullet often measures close to the maximum 2.260 inches. In contrast, heavy 300 grain subsonic bullets are exceptionally long. To maintain the 2.260 inch overall length restriction, these massive bullets must be seated very deeply into the brass case, which significantly reduces the available powder capacity and requires specific subsonic reloading data.
400 Legend Chamber And Cartridge Dimensions
The relationship between the 400 Legend cartridge and the firearm chamber is critical for reliable functionality. Because it lacks a bottleneck shoulder, the 400 Legend cartridge headspaces entirely on the case mouth.
This means the flat forward edge of the brass casing physically stops against a machined ledge inside the barrel chamber. Proper case length is absolutely mandatory. If the brass stretches beyond 1.650 inches, the cartridge will pinch in the chamber throat, which can prevent the bolt from closing or cause dangerous pressure spikes upon firing. Additionally, because the cartridge headspaces on the case mouth, reloaders must apply a taper crimp rather than a heavy roll crimp.
400 Legend Dimensions vs Similar Cartridges
To understand the 400 Legend size profile, it is helpful to compare it against other popular straight-walled hunting cartridges.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Rim / Base Diameter | Maximum Pressure | Source |
| 400 Legend | 0.4005 in | 1.650 in | 2.260 in | 0.422 in / 0.440 in | 45,000 psi | SAAMI |
| 350 Legend | 0.357 in | 1.710 in | 2.260 in | 0.378 in / 0.390 in | 55,000 psi | SAAMI |
| 450 Bushmaster | 0.452 in | 1.700 in | 2.260 in | 0.473 in / 0.500 in | 38,500 psi | SAAMI |
| 360 Buckhammer | 0.358 in | 1.800 in | 2.500 in | 0.506 in / 0.419 in | 50,000 psi | SAAMI |
400 Legend vs 350 Legend Dimensions
The 400 Legend was specifically engineered by Winchester to bridge the gap between the smaller 350 Legend and the massive 450 Bushmaster. While both Legend cartridges target the same hunting regulations and AR-15 compatibility, they are dimensionally distinct.
- Bullet Diameter: The 400 Legend utilizes a much wider 0.4005 inch rifle bullet compared to the 0.357 inch bullet used by the 350 Legend.
- Case Width: The 400 Legend is a significantly fatter cartridge, utilizing a 0.440 inch base and a 0.422 inch rim. The 350 Legend uses a narrower 0.390 inch base and a 0.378 inch rim.
- Parts Compatibility: Because of its 0.422 inch rim, a 400 Legend requires a 6.8 SPC bolt carrier group. The 350 Legend uses a standard 223 Remington bolt carrier group.
- Case Length: The 400 Legend case is shorter at 1.650 inches versus the 1.710 inches of the 350 Legend. This slightly shorter case leaves enough forward space in the magazine to accommodate the wider, blunter .40 caliber projectiles.
400 Legend SAAMI vs C.I.P. Dimensions
Cartridge dimensions and safe pressure limits are strictly governed by SAAMI in the United States. Winchester designed the cartridge and submitted it to SAAMI, which officially standardized the 400 Legend in early 2023.
SAAMI lists the maximum average pressure for the 400 Legend at 45,000 psi, measured via conformal piezoelectric transducers. C.I.P. in Europe does not always immediately adopt highly specialized American hunting cartridges. However, any ammunition manufactured to SAAMI specifications is considered safe and standard for use globally.
400 Legend Bullet Weight And Dimensions
The 400 Legend is loaded heavily in two completely different bullet weight categories that change how the internal dimensions of the cartridge are configured.
- Supersonic (190 to 215 grain): These bullets are designed to fly significantly faster than the speed of sound. They fit perfectly within the 1.650 inch case, leaving maximum case capacity for the gunpowder required to push them to high velocities for deer and hog hunting.
- Subsonic (300 grain): These massive, heavy bullets are designed to stay below the speed of sound, making them exceptionally quiet when fired through a suppressor. To maintain the 2.260 inch overall length restriction, these long bullets must be seated very deeply into the brass case, which significantly reduces the available powder capacity.
Bullet weight does not alter the external brass case dimensions, but the manufacturer must carefully manage bullet seating depth to ensure safe chamber pressures.
Why 400 Legend Dimensions Matter
Understanding the specific 400 Legend measurements is essential for several practical reasons.
- Hunting Regulations: The 1.650 inch case length perfectly complies with Midwestern straight-walled cartridge laws, which typically cap the maximum case length at 1.800 inches.
- Parts Compatibility: Knowing that the rim diameter (0.422 inches) matches the 6.8 SPC allows shooters to build a 400 Legend AR-15 using standard lower receivers and 6.8 SPC bolts. Only the barrel and the magazines need to be changed.
- Reloading Safety: Because the cartridge headspaces on the case mouth, reloaders must meticulously measure their brass. Cases trimmed too short will suffer light primer strikes, and cases left too long will jam in the chamber.
Manufacturer Specifications vs Independent Measurements
If you use calipers to measure factory 400 Legend ammunition from Winchester, the numbers will rarely match the SAAMI maximum specifications exactly.
SAAMI publishes maximum allowable dimensions to ensure absolute safety and interoperability. Ammunition manufacturers purposefully produce their cases slightly smaller than these maximums. For example, the maximum case length is 1.650 inches, but measuring a factory cartridge might reveal a case length of 1.642 inches. This built-in negative tolerance margin guarantees that the ammunition will chamber reliably in the field, even if the rifle is fouled from carbon buildup.
Common Questions
What are the dimensions of the 400 Legend?
The key maximum dimensions are a bullet diameter of 0.4005 inches, a case length of 1.650 inches, and an overall cartridge length of 2.260 inches.
What is the 400 Legend case length?
The maximum SAAMI case length is 1.650 inches (41.91 mm).
What is the 400 Legend overall length?
The maximum overall length (OAL) is 2.260 inches (57.40 mm), designed to fit standard AR-15 magazines.
What is the 400 Legend bullet diameter?
The SAAMI maximum bullet diameter is 0.4005 inches.
What is the 400 Legend rim diameter?
The rim diameter measures 0.422 inches, identical to the 6.8 SPC.
What is the 400 Legend case diameter?
The case diameter at the base is 0.440 inches, tapering slightly to 0.4267 inches at the case mouth.
What is the 400 Legend case capacity?
The 400 Legend holds approximately 44.0 grains of water, depending on the thickness of the specific brass casing.
What is the maximum pressure for the 400 Legend?
The SAAMI maximum average pressure is strictly capped at 45,000 psi.
How do 400 Legend and 350 Legend dimensions compare?
They share the same maximum overall length (2.260 in), but the 400 Legend uses a slightly shorter case (1.650 in), a wider base (0.440 in), a wider rim (0.422 in), and a much larger 0.4005 inch bullet.
Does the 400 Legend use the same bolt as a 350 Legend?
No. The 350 Legend uses a 0.378 inch rim (standard 223 Remington bolt), while the 400 Legend uses a 0.422 inch rim (standard 6.8 SPC bolt).