The key 350 Legend case dimensions include a maximum case length of 1.710 inches (43.43 mm) and a maximum overall cartridge length of 2.260 inches (57.40 mm). The case features a 0.378-inch rim diameter, a 0.390-inch base diameter, and a 0.378-inch mouth diameter. Because it is a straight-walled cartridge, it lacks a traditional shoulder diameter and neck length. When reviewing these measurements, note that published dimensions may include nominal values, maximum limits, or specific tolerances depending on the specification source. These exact dimensions allow the cartridge to utilize standard AR-15 bolt faces while complying with hunting regulations that require straight-walled cases.
350 Legend Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 1.710 | 43.43 | Maximum | SAAMI | Trim-to length is typically 1.700″ |
| Rim Diameter | 0.378 | 9.60 | Maximum | SAAMI | Matches the 5.56 / .223 bolt face |
| Base Diameter | 0.390 | 9.91 | Maximum | SAAMI | Wider than the .223 Remington base |
| Shoulder Diameter | N/A | N/A | Nominal | SAAMI | Straight-walled case without a shoulder |
| Neck (Mouth) Diameter | 0.378 | 9.60 | Maximum | SAAMI | Must accommodate a 0.355 to 0.357-inch bullet |
| Neck Length | N/A | N/A | Nominal | SAAMI | Straight-walled case |
| Shoulder Angle | N/A | N/A | Nominal | SAAMI | Straight-walled case |
| Overall Cartridge Length | 2.260 | 57.40 | Maximum | SAAMI | Constrained by standard AR-15 magazine internal limits |
| Case Capacity | ~36.5 gr H2O | ~2.36 cm³ | Measured Range | Industry / Mfg | Varies based on brass brand and wall thickness |
| Maximum Pressure | 55,000 psi | 380 MPa | Maximum Average | SAAMI | Standardized high-pressure limit |
Understanding The 350 Legend Case Dimensions
To fully grasp how the 350 Legend operates, it helps to understand what each specific measurement dictates inside the firearm:
- Case length: Measured from the base of the rim to the case mouth, this dictates how far the brass extends into the chamber. Because this cartridge headspaces on the case mouth, exact case length is critical.
- Rim diameter: The width of the extraction rim at the very bottom of the case. Because this matches the 5.56 NATO perfectly, the 350 Legend requires no bolt face modifications in an AR-15.
- Base diameter: The width of the case body just above the extractor groove. At 0.390 inches, it is wider than the standard .223 Remington case.
- Shoulder and neck diameter: As a straight-walled cartridge, it has no shoulder. The case tapers directly from the 0.390-inch base to a 0.378-inch case mouth (often referred to as neck diameter in bottleneck terms).
- Overall cartridge length: The total length of the assembled round (brass plus bullet). This must not exceed 2.260 inches to feed reliably through AR-15 magazine wells.
- Case capacity: The internal volume of the case, typically measured in grains of water (H2O), dictating how much powder can be safely loaded.
350 Legend Case Dimensions In Inches And Millimeters
A reliable 350 Legend dimensions chart makes conversions simple. Here are the primary 350 Legend dimensions in mm and inches, reflecting official maximum and nominal tolerances:
| Dimension | Inches | Millimeters |
| Maximum Case Length | 1.710″ | 43.43 mm |
| Base Diameter | 0.390″ | 9.91 mm |
| Rim Diameter | 0.378″ | 9.60 mm |
| Mouth / Neck Diameter | 0.378″ | 9.60 mm |
| Overall Cartridge Length | 2.260″ | 57.40 mm |
350 Legend Case Length
The SAAMI maximum 350 Legend case length is standardized at 1.710 inches (43.43 mm). Unlike bottleneck cartridges that headspace on a shoulder, the 350 Legend headspaces on the mouth of the case. This means the physical edge of the brass rests against a tiny ledge inside the chamber to stop the cartridge from sliding forward. If the case length is too short, the firing pin may fail to reliably ignite the primer. If the case length stretches beyond 1.710 inches, the brass can pinch inside the chamber throat and cause a catastrophic pressure spike. Reloaders typically trim this brass to 1.700 inches to ensure perfect safety and function.
350 Legend Base And Rim Dimensions
The 350 Legend was heavily marketed as an AR-15 compatible cartridge, achieved by using a 0.378-inch rim diameter. This allows shooters to use a standard 5.56 NATO bolt carrier group. However, the base diameter directly ahead of the extractor groove measures 0.390 inches. This distinct base width provides a slight taper up to the 0.378-inch mouth, ensuring smoother extraction from the chamber than a perfectly cylindrical case would allow.
350 Legend Shoulder And Neck Dimensions
The defining characteristic of the 350 Legend is its lack of a shoulder. To comply with straight-walled cartridge hunting regulations in states like Ohio, Michigan, and Iowa, Winchester designed the case without any bottleneck geometry. The brass body simply tapers from the 0.390-inch base to the 0.378-inch mouth. Because there is no neck, bullet tension relies entirely on the grip of the straight case walls and a very careful taper crimp applied during the reloading process.
350 Legend Case Capacity
While external dimensions are heavily standardized, internal 350 Legend case capacity is not completely uniform. Capacity typically hovers around 36.5 grains of water (H2O). This measurement varies slightly depending on whether you are using Winchester factory brass or aftermarket brass from companies like Starline. Thicker brass walls will reduce this internal volume. Because the 350 Legend operates at a high pressure limit of 55,000 psi, reloaders must be cautious when changing brass brands, as less internal capacity will increase pressure for a given powder charge.
350 Legend Case Dimensions vs 5.56 NATO
Many assume the 350 Legend is simply a .223 Remington case blown outward to hold a larger bullet. This is dimensionally incorrect. Below is a comparison:
| Dimension | 350 Legend | 5.56 NATO / .223 Remington | Source |
| Case Length | 1.710″ (43.43 mm) | 1.760″ (44.70 mm) | SAAMI |
| Rim Diameter | 0.378″ (9.60 mm) | 0.378″ (9.60 mm) | SAAMI |
| Base Diameter | 0.390″ (9.91 mm) | 0.377″ (9.57 mm) | SAAMI |
| Shoulder Diameter | N/A (Straight) | 0.354″ (8.99 mm) | SAAMI |
| Neck Diameter | 0.378″ (9.60 mm) | 0.253″ (6.43 mm) | SAAMI |
| Overall Cartridge Length | 2.260″ (57.40 mm) | 2.260″ (57.40 mm) | SAAMI |
The critical difference is the base diameter. The 5.56 NATO has a 0.377-inch base, while the 350 Legend uses a wider 0.390-inch base. This extra width is required to safely hold a .357 caliber bullet while maintaining acceptable brass wall thickness.
350 Legend Case Dimensions vs 450 Bushmaster
Both the 350 Legend and the 450 Bushmaster were designed to offer straight-walled hunting capabilities in the AR-15 platform, but they are built on completely different case architectures.
The 450 Bushmaster utilizes a much wider 0.473-inch rim (requiring a specialized bolt face) and a massive 0.500-inch base diameter. While the 450 Bushmaster delivers significantly more kinetic energy and uses a larger .452-inch bullet, its wider case dimensions mean standard AR-15 magazines can only hold them in a single-stack configuration. The narrower 350 Legend dimensions allow it to feed in a staggered, double-stack orientation, though it still requires specialized magazines with modified internal ribs to accommodate the wider 0.390-inch base.
350 Legend Cartridge And Chamber Dimensions
Because straight-walled cases lack a shoulder for headspacing, chamber tolerances are highly critical. The 350 Legend headspaces on the forward rim (the mouth) of the case. Inside the rifle chamber, there is a tiny machined step. When the bolt pushes the round forward, the flat brass edge of the case mouth stops against this step. If a reloader applies a heavy roll crimp to the ammunition, the edge of the brass bends inward into the bullet. This removes the flat edge needed for headspacing, which can allow the cartridge to slide too far forward into the barrel. Only a gentle taper crimp should be used on 350 Legend ammunition.
350 Legend Case Forming And Resizing
A major point of confusion for reloaders involves converting brass. You cannot safely form 350 Legend brass from standard .223 Remington or 5.56 NATO cases. Because the .223 Remington has a base diameter of 0.377 inches, and the 350 Legend chamber is cut for a 0.390-inch base, firing a modified .223 case in a 350 Legend rifle will cause the brass to bulge dangerously near the web. This can lead to case ruptures. Reloaders must purchase dedicated 350 Legend brass or use 0.390-inch “basic” cylindrical brass specifically manufactured for this geometry.
Manufacturer Specifications vs Actual Measurements
When researching 350 Legend dimensions, it is critical to distinguish between maximum specifications and actual measurements. SAAMI dictates a maximum average pressure of 55,000 psi.
Similarly, the SAAMI maximum case length is 1.710 inches. If you measure a brand-new factory cartridge with calipers, you will often find it measures closer to 1.700 inches. Manufacturers intentionally produce brass slightly under the absolute maximum limit. This built-in tolerance guarantees that their ammunition will chamber easily and safely across a vast array of different rifle brands, accounting for minor chamber variations.
Common Questions
What are the 350 Legend case dimensions?
Key dimensions include a 1.710-inch maximum case length, 0.378-inch rim diameter, 0.390-inch base diameter, and a 0.378-inch mouth diameter.
What is the 350 Legend case length?
The official SAAMI maximum case length for the 350 Legend is 1.710 inches (43.43 mm).
What is the 350 Legend base diameter?
The nominal maximum base diameter is 0.390 inches.
What is the 350 Legend rim diameter?
The rim diameter is 0.378 inches, allowing it to utilize standard 5.56 NATO and .223 Remington bolt faces.
What is the 350 Legend shoulder diameter?
The 350 Legend is a straight-walled cartridge and does not have a shoulder.
What is the 350 Legend neck diameter?
As a straight-walled cartridge, it has a mouth diameter of 0.378 inches rather than a traditional neck.
What is the 350 Legend case capacity?
Depending on the brass manufacturer and wall thickness, capacity is approximately 36.5 grains of water (H2O).
Is 350 Legend case length the same as 5.56?
No. The 350 Legend case length is 1.710 inches, whereas the 5.56 NATO case length is 1.760 inches.
How does 350 Legend case size compare with 5.56?
They share the exact same rim diameter and overall assembled cartridge length (2.260 inches). However, the 350 Legend has a wider base (0.390 inches vs 0.377 inches) and lacks a shoulder.
Can I make 350 Legend brass from .223?
No. The base of the .223 Remington is significantly narrower than the 350 Legend chamber. Attempting to fireform .223 brass into a 350 Legend chamber creates a dangerous bulge and risks a case rupture.
What is the 350 Legend overall cartridge length?
The maximum overall length (OAL) is 2.260 inches (57.40 mm), allowing it to fit standard AR-15 magazine wells.
What is the 350 Legend maximum pressure?
The SAAMI maximum average pressure for the 350 Legend is 55,000 psi.