The .357 Magnum is a rimmed, straight walled centerfire revolver cartridge featuring a standard maximum bullet diameter of .357 inches (9.07 mm). The maximum case length is 1.290 inches (32.77 mm), and the maximum overall cartridge length (OAL) is specified at 1.590 inches (40.39 mm) to ensure compatibility with revolver cylinders. The case utilizes a prominent rim diameter of .440 inches (11.18 mm) and maintains a uniform straight body diameter of .379 inches (9.63 mm) from base to neck. Ammunition for this caliber is most commonly found in 125 grain and 158 grain bullet weights. Exact dimensions and pressures can vary slightly depending on allowable manufacturing tolerances and whether you reference SAAMI specifications or European C.I.P. standards.
.357 Magnum Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | .357 in (9.07 mm) | SAAMI / C.I.P. | Standard for jacketed bullets; lead bullets often measure .358 in. |
| Case Length | 1.290 in (32.77 mm) | SAAMI | Maximum case length; trim-to length is typically 1.280 in. |
| Overall Cartridge Length | 1.590 in (40.39 mm) | SAAMI | Maximum overall length for standard revolver cylinders. |
| Rim Diameter | .440 in (11.18 mm) | SAAMI | Maximum rim diameter. |
| Case Diameter | .379 in (9.63 mm) | SAAMI | Maximum diameter measured at the base. |
| Shoulder Diameter | N/A | N/A | Straight walled cartridge; no shoulder. |
| Neck Diameter | .379 in (9.63 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | .379 in (9.63 mm) | SAAMI | Uniform with the neck due to the straight walled design. |
| Case Capacity | 26.2 to 27.0 gr H2O | Industry Standard | Varies slightly based on brass manufacturer and wall thickness. |
| Maximum Pressure | 35,000 psi | SAAMI | C.I.P. maximum is 300 MPa (approximately 43,500 psi). |
Understanding The .357 Magnum Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the .357 Magnum, this is specified as .357 inches. This dimension ensures the projectile seals properly within the barrel’s rifling to trap expanding gases and generate high velocity.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 1.290 inches. This extended case length is a deliberate design choice to prevent the high pressure cartridge from chambering in older firearms designed for lower pressure ammunition.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 1.590 inches. OAL directly influences whether a cartridge will fit inside the cylinder of a revolver and allow it to rotate freely.
- Rim Diameter: The diameter of the flange at the very bottom of the case (.440 inches). The revolver cylinder extracts the spent casings by pushing against this rim.
- Case Diameter: The width of the cartridge body. The .357 Magnum is a straight walled case, meaning the base diameter (.379 inches) and the neck diameter (.379 inches) are identical on unfired brass.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging around 26.2 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 35,000 psi for the .357 Magnum, which requires a robust, modern steel firearm to handle safely.
.357 Magnum Cartridge Dimensions In Inches And Millimeters
For engineers, reloaders, and international shooters, below are the primary .357 Magnum measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Max) | Millimeters (Equivalent) |
| Bullet Diameter | .357 in | 9.07 mm |
| Case Length | 1.290 in | 32.77 mm |
| Overall Length | 1.590 in | 40.39 mm |
| Rim Diameter | .440 in | 11.18 mm |
| Base Diameter | .379 in | 9.63 mm |
| Neck Diameter | .379 in | 9.63 mm |
.357 Magnum Case Dimensions
The .357 Magnum is defined by a rimmed, straight walled case. The official maximum case length is 1.290 inches (32.77 mm), with a nominal trim-to length for reloaders sitting at 1.280 inches. The base diameter measures .379 inches, and the rim diameter extends significantly wider to .440 inches.
Because the .357 Magnum operates at a high pressure of 35,000 psi, the brass case walls must be manufactured with adequate thickness to prevent splitting upon ignition. This thick brass construction, combined with the straight walled design, results in an internal case capacity of roughly 26.2 to 27.0 grains of water. This capacity allows reloaders to use large volumes of slow burning magnum pistol powders to achieve extreme velocities.
.357 Magnum Bullet Diameter
The standardized maximum bullet diameter for the .357 Magnum is .357 inches (9.07 mm) for jacketed bullets. However, reloaders often use .358 inch diameter bullets when loading hard cast lead projectiles. The slightly wider lead bullet seals the bore more effectively, which prevents hot gases from cutting past the bullet and causing severe lead fouling in the barrel.
The standard .357 Magnum barrel features a groove diameter of .355 to .356 inches and a bore diameter of .346 inches. Firing a .357 inch bullet down a .355 inch groove diameter forces the copper jacket to engrave tightly into the rifling, creating the necessary spin to stabilize the projectile accurately in flight.
.357 Magnum Overall Length
The SAAMI maximum overall cartridge length (OAL) for the .357 Magnum is 1.590 inches (40.39 mm). This number is a hard limit designed to guarantee that the bullet tip will not protrude past the front face of a standard revolver cylinder. If a cartridge exceeds this length, it will bind against the forcing cone of the barrel and physically prevent the cylinder from turning.
Typical factory cartridge length varies based on the bullet profile. A classic 158 grain semi-wadcutter hunting round often measures close to the maximum 1.590 inches. In contrast, lightweight 125 grain jacketed hollow points are physically shorter and are typically seated to an overall length of 1.570 to 1.580 inches to ensure proper powder compression and case tension.
.357 Magnum Chamber And Cartridge Dimensions
The relationship between the .357 Magnum cartridge and the firearm’s chamber is uniquely adapted for revolvers. Unlike semi-automatic pistol cartridges that headspace on the case mouth, the .357 Magnum cartridge headspaces on its .440 inch rim.
This means the protruding rim of the brass casing physically stops against the rear cylinder face. Because it headspaces on the rim, the overall case length does not dictate how deep the cartridge drops into the chamber. This design allows revolver cartridges to employ a heavy roll crimp. A roll crimp physically bends the case mouth into a groove on the bullet known as a cannelure. This heavy crimp is absolutely mandatory for the .357 Magnum to prevent the bullets in unfired cylinders from backing out of their cases under the massive recoil of firing.
.357 Magnum Dimensions vs Similar Cartridges
To understand the .357 Magnum size profile, it is helpful to compare it against other popular handgun cartridges. Note that dimensional similarities do not imply ammunition interchangeability unless strictly specified by the manufacturer.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Rim Diameter | Maximum Pressure | Source |
| .357 Magnum | .357 in | 1.290 in | 1.590 in | .440 in | 35,000 psi | SAAMI |
| .38 Special | .357 in | 1.155 in | 1.550 in | .440 in | 17,000 psi | SAAMI |
| .357 SIG | .355 in | .865 in | 1.140 in | .424 in | 40,000 psi | SAAMI |
| 9mm Luger | .355 in | .754 in | 1.169 in | .394 in | 35,000 psi | SAAMI |
| .44 Magnum | .429 in | 1.285 in | 1.610 in | .514 in | 36,000 psi | SAAMI |
.357 Magnum vs .38 Special Dimensions
The .357 Magnum and the .38 Special are deeply connected, but their dimensional differences are a matter of critical safety.
- Bullet and Rim Dimensions: Both cartridges use the exact same .357 inch bullet diameter, the exact same .379 inch base diameter, and the exact same .440 inch rim diameter.
- Case Length Difference: The .357 Magnum case (1.290 inches) is intentionally manufactured exactly 0.135 inches longer than the .38 Special case (1.155 inches).
- Pressure Differences: The .357 Magnum generates 35,000 psi, while standard .38 Special operates at a much lower 17,000 psi.
Because of this specific dimensional design, a short .38 Special cartridge can be loaded and fired safely in any .357 Magnum revolver. However, the elongated 1.290 inch case of the .357 Magnum physically prevents it from fully chambering in an older, weaker .38 Special revolver. This dimensional offset protects shooters from explosive firearm failures.
.357 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.
While the physical dimensional specifications for the .357 Magnum are functionally identical between the two bodies to ensure global compatibility, the way they measure and report pressure differs significantly.
- SAAMI lists the maximum average pressure for the .357 Magnum at 35,000 psi, measured via conformal piezoelectric transducers.
- C.I.P. lists the maximum pressure for the exact same cartridge at 300 MPa, which translates to approximately 43,500 psi.
These are not contradictory safety standards. They are the result of different testing methodologies, transducer placement locations, and historical pressure measurement conversions. Ammunition loaded to SAAMI specs is completely safe in C.I.P. proofed firearms, and vice versa.
.357 Magnum Bullet Weight And Dimensions
The .357 Magnum is widely loaded in several common bullet weights, which alter how the internal dimensions of the cartridge are configured.
- 110 to 125 grain: These lightweight, hollow point bullets are physically short. They leave maximum case capacity for heavy charges of gunpowder, resulting in massive velocities often exceeding 1,450 feet per second.
- 158 grain: The traditional standard weight for the caliber. These longer bullets take up more space inside the brass case, slightly reducing powder capacity but offering incredible penetration for hunting or silhouette shooting.
- 180 grain: Extremely heavy hard cast bullets designed for hunting large game. To maintain the 1.590 inch maximum revolver length, these long bullets must be seated very deep into the powder column.
Bullet weight does not change the standardized external brass case dimensions. However, because a heavier bullet is physically longer, the manufacturer must adjust the seating depth to ensure the loaded round still fits inside the cylinder.
Why .357 Magnum Dimensions Matter
Understanding the specific .357 Magnum measurements is essential for several practical reasons.
- Cylinder Binding: The strict 1.590 inch overall length defines whether a cartridge will function in a revolver. Handloaders who seat their bullets too shallow will lock up their firearm the moment the cylinder tries to rotate past the barrel forcing cone.
- Crimping Requirements: Because the case measures 1.290 inches, reloaders must accurately trim all their brass to the exact same length (typically 1.280 inches). If case lengths vary, the reloading die will apply inconsistent roll crimps, leading to bullet jump under heavy recoil.
- Lever Action Compatibility: Many shooters pair their revolver with a lever action rifle chambered in .357 Magnum. These rifles rely heavily on exact overall cartridge lengths to transfer rounds smoothly from the magazine tube to the chamber without jamming the elevator mechanism.
Manufacturer Specifications vs Independent Measurements
If you use calipers to measure factory .357 Magnum ammunition from companies like Federal, Winchester, or Hornady, the numbers will rarely match the SAAMI maximum specifications exactly.
SAAMI and C.I.P. publish maximum allowable dimensions to ensure absolute safety and compatibility across all firearm brands. Ammunition manufacturers purposefully produce their cases slightly smaller than these maximums. For example, measuring a factory cartridge and finding a case length of 1.282 inches or an OAL of 1.575 inches does not mean the ammunition is defective. It means the manufacturer built in a reliable negative tolerance margin to guarantee the ammunition will load easily into tight match grade revolver cylinders.
Common Questions
What are the dimensions of the .357 Magnum?
The key maximum dimensions are a bullet diameter of .357 inches, a case length of 1.290 inches, and an overall cartridge length of 1.590 inches.
What is the .357 Magnum case length?
The maximum SAAMI case length is 1.290 inches (32.77 mm).
What is the .357 Magnum overall length?
The maximum overall length (OAL) is 1.590 inches (40.39 mm).
What is the .357 Magnum bullet diameter?
The standard bullet diameter is .357 inches for jacketed bullets and often .358 inches for lead bullets.
What is the .357 Magnum rim diameter?
The rim diameter measures .440 inches (11.18 mm).
What is the .357 Magnum case diameter?
The .357 Magnum is a straight walled cartridge, meaning the case diameter is uniformly .379 inches from the base to the neck.
What is the difference between .357 Magnum and 9mm dimensions?
The .357 Magnum uses a .357 inch bullet and a long 1.290 inch rimmed case. The 9mm uses a slightly smaller .355 inch bullet and a very short .754 inch rimless case.
How do .357 Magnum and .38 Special dimensions compare?
They share the exact same bullet diameter and case width, but the .357 Magnum case is intentionally 0.135 inches longer to prevent it from chambering in weaker .38 Special firearms.
What is the maximum overall length of the .357 Magnum?
The absolute maximum allowed by SAAMI is 1.590 inches to ensure the bullet does not bind against the front of a revolver cylinder.
What is the .357 Magnum maximum pressure?
The SAAMI maximum average pressure is 35,000 psi.