The exact bullet diameter of the 400 Legend is 0.4005 inches (10.17 millimeters). Introduced by Winchester in 2023, this straight-wall cartridge uses .400-caliber class projectiles purposely designed for hunting rather than repurposing existing handgun bullets. Bullet diameter represents the actual outer width of the projectile itself, distinguishing it from bore diameter (0.3900 inches) and groove diameter (0.4005 inches). The SAAMI specification strictly requires a 0.4005-inch nominal maximum diameter so the bullet can form a perfect gas seal as it engraves into the barrel’s rifling. Verifying these exact dimensions is essential because the “400” designation is simply a numerical name, not a precise manufacturing measurement.
400 Legend Bullet Diameter
| Specification | 400 Legend |
| Nominal Bullet Diameter | 0.4005 in |
| Bullet Diameter In Inches | 0.4005 in |
| Bullet Diameter In Millimeters | 10.17 mm |
| Groove Diameter | 0.4005 in |
| Bore Diameter | 0.3900 in |
| Typical Bullet Weights | 190 gr – 300 gr |
| Case Length | 1.650 in |
| Overall Cartridge Length | 2.260 in |
| Maximum Pressure | 45,000 PSI |
Explain The Specifications
What Is The 400 Legend Bullet Diameter?
The nominal bullet diameter for the 400 Legend is 0.4005 inches. Standardized by SAAMI, the cartridge was developed to provide more energy than the 350 Legend while complying with straight-wall hunting regulations. The “400” name is a marketing designation for its .40-caliber class projectiles.
400 Legend Bullet Diameter In Inches
In imperial measurements, the 400 Legend projectile measures exactly 0.4005 inches with a SAAMI manufacturing tolerance of +0.0000 / -0.0030 inches.This size matches the diameter of existing .40-caliber pistol bullets, though the 400 Legend utilizes custom heavy-jacketed rifle projectiles.
400 Legend Bullet Diameter In Millimeters
When converted to the metric system, a 0.4005-inch bullet equals 10.17 millimeters (specifically 10.173 mm). Metric technical drawings reference the projectile diameter as 10.173 mm -0.076 mm.
400 Legend Bullet vs Bore Diameter
Bore diameter refers to the inside diameter of the barrel before rifling grooves are cut (measured land-to-land). For the 400 Legend, the bore diameter is 0.3900 inches (9.91 mm).The bullet diameter (0.4005 inches) is intentionally larger than the bore diameter so the jacket material swages into the rifling grooves upon firing to form a gas-tight seal.
400 Legend Groove Diameter
Groove diameter is the measurement from the bottom of one rifling groove to the bottom of the opposite groove. The 400 Legend barrel specification calls for a groove diameter of 0.4005 inches (10.17 mm), perfectly matching the maximum nominal bullet diameter to ensure full engagement with the rifling.
400 Legend Bullet Weights
While bullet size remains fixed at 0.4005 inches, projectile mass varies based on application. Factory offerings primarily feature 190-grain to 215-grain soft-point and polymer-tipped loads optimized for medium-to-large game, along with heavy 300-grain subsonic options.
400 Legend Dimensions
The official SAAMI dimensional drawing defines the cartridge geometry to ensure safe chambering across all manufactured firearms.
| Dimension | Measurement |
| Bullet Diameter | 0.4005 in (10.17 mm) |
| Bore Diameter | 0.3900 in (9.91 mm) |
| Groove Diameter | 0.4005 in (10.17 mm) |
| Case Length | 1.650 in (41.91 mm) |
| Overall Cartridge Length | 2.260 in (57.40 mm) |
| Base Diameter | 0.4400 in (11.18 mm) |
| Neck Diameter | 0.4267 in (10.84 mm) |
| Rim Diameter | 0.4220 in (10.72 mm) |
| Maximum Pressure | 45,000 PSI |
Bullet Weights
Factory 400 Legend ammunition focuses on robust construction to deliver momentum and rapid expansion within straight-wall state hunting zones. Bullet weight alters projectile length and sectional density, but the 0.4005-inch diameter remains constant.
| Bullet Weight | Example Load | Bullet Type | Advertised Velocity |
| 190 gr | Winchester Deer Season XP | Extreme Point (Polymer Tip) | 2,400 fps |
| 210 gr | Hornady American Whitetail | InterLock SP | 2,200 fps |
| 215 gr | Winchester Power-Point | Soft Point (SP) | 2,250 fps |
| 300 gr | Winchester Super Suppressed | Open Tip (OT) | 1,060 fps |
400 Legend vs 10mm Auto
While both cartridges share a bullet diameter in the exact same .400-caliber family, they are built on drastically different case platforms for completely different purposes.
| Specification | 400 Legend | 10mm Auto |
| Bullet Diameter | 0.4005 in | 0.4000 in |
| Typical Bullet Weight | 190 gr – 215 gr | 180 gr – 200 gr |
| Case Length | 1.650 in | 0.992 in |
| Overall Length | 2.260 in | 1.250 in |
| Typical Velocity | 2,250 – 2,400 fps | 1,150 – 1,250 fps |
| Typical Muzzle Energy | 2,300 – 2,430 ft-lbs | 550 – 650 ft-lbs |
Note: Similar bullet diameters do not make cartridges interchangeable. The 400 Legend requires dedicated heavy-jacket rifle bullets to withstand its 45,000 PSI operating pressures and 2,400 fps velocities, which would cause standard pistol bullets to fragment prematurely.
400 Legend vs 350 Legend
Shooters frequently evaluate the 400 Legend against its predecessor, the 350 Legend, for straight-wall hunting legality. Their exact projectile diameters differ significantly to serve different performance tiers.
| Specification | 400 Legend | 350 Legend |
| Bullet Diameter | 0.4005 in | 0.3570 in |
| Diameter In mm | 10.17 mm | 9.07 mm |
| Typical Bullet Weight | 190 gr – 215 gr | 150 gr – 180 gr |
| Case Length | 1.650 in | 1.710 in |
| Overall Length | 2.260 in | 2.260 in |
The 400 Legend uses a true 0.4005-inch rifle bullet diameter, while the 350 Legend relies on a narrower 0.3570-inch diameter projectile.The 400 Legend case is slightly shorter (1.650 in vs 1.710 in) to maintain identical 2.260-inch overall lengths for AR-15 magazine compatibility.
400 Legend Bullet Diameter: Exact Measurement
The exact bullet diameter of the 400 Legend is 0.4005 inches (10.17 mm).
Understanding standard firearm dimensional terms helps explain why multiple measurements exist for one barrel:
- Nominal Bullet Diameter (0.4005 in): The physical outer diameter of the unfired projectile.
- Bore Diameter (0.3900 in): The minimum inner barrel diameter across the raised lands.
- Groove Diameter (0.4005 in): The maximum inner barrel diameter across the cut grooves, matching the bullet’s width to establish an airtight seal upon ignition.
Frequently Asked Questions
What is the bullet diameter of 400 Legend?
The exact bullet diameter of the 400 Legend is 0.4005 inches.
What is 400 Legend bullet diameter in mm?
In metric units, the 400 Legend projectile diameter measures 10.17 mm.
Is 400 Legend a .40 caliber bullet?
Yes. The cartridge utilizes a standard .40-caliber class rifle projectile, sharing the same base diameter family as the .40 S&W and 10mm Auto.
What is the bore diameter of 400 Legend?
The SAAMI specification for 400 Legend bore diameter (land-to-land measurement) is 0.3900 inches (9.91 mm).
What is the groove diameter of 400 Legend?
The SAAMI specification for 400 Legend groove diameter (groove-to-groove measurement) is 0.4005 inches (10.17 mm).
Is 400 Legend the same diameter as 10mm?
They are in the exact same caliber family (0.4000 vs 0.4005 inches), but the cartridges are vastly different. The 400 Legend uses heavily jacketed rifle bullets designed for much higher velocities.
Is 400 Legend the same diameter as 350 Legend?
No. The 400 Legend uses a 0.4005-inch bullet diameter, whereas the 350 Legend uses a smaller 0.3570-inch bullet diameter.
What bullet weights are available for 400 Legend?
Factory ammunition currently features hunting options ranging from 190-grain to 215-grain projectiles, as well as heavy 300-grain subsonic loads for suppressed shooting.
What is the case diameter of 400 Legend?
The 400 Legend has a base diameter of 0.4400 inches, tapering to a neck diameter of 0.4267 inches, with a rebated rim diameter of 0.4220 inches.
How does 400 Legend bullet diameter compare with 350 Legend?
The 400 Legend is 0.0435 inches larger in projectile diameter (0.4005 in vs 0.3570 in) than the 350 Legend.
How does 400 Legend bullet diameter compare with 450 Bushmaster?
The 400 Legend uses a 0.4005-inch bullet, which is narrower than the 450 Bushmaster’s 0.4520-inch bullet. This smaller diameter contributes to the 400 Legend’s 20% reduction in felt recoil compared to the Bushmaster.