The .40 S&W (10x22mm) is a rimless, straight walled centerfire handgun cartridge featuring a standard maximum bullet diameter of 0.400 inches (10.16 mm). The maximum case length is 0.850 inches (21.59 mm), and the maximum overall cartridge length (OAL) is specified at 1.135 inches (28.83 mm) to ensure compatibility with standard semi automatic pistol magazines designed around medium frames. The case utilizes a rim diameter of 0.424 inches (10.77 mm) and maintains a nearly uniform straight body diameter of 0.424 inches (10.77 mm) at the base, tapering microscopically to 0.423 inches (10.74 mm) at the case mouth. Ammunition for this caliber is most commonly found in 155 grain, 165 grain, and 180 grain bullet weights. Exact dimensions and operating pressures can vary slightly depending on manufacturing tolerances and whether you reference American SAAMI specifications or European C.I.P. standards.
.40 S&W Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.400 in (10.16 mm) | SAAMI / C.I.P. | Standard for .40 caliber handguns. |
| Case Length | 0.850 in (21.59 mm) | SAAMI | Maximum case length; trim to length is typically 0.840 in. |
| Overall Cartridge Length | 1.135 in (28.83 mm) | SAAMI | Maximum overall length for standard magazines. |
| Rim Diameter | 0.424 in (10.77 mm) | SAAMI | Maximum rim diameter. |
| Case Diameter (Base) | 0.424 in (10.77 mm) | SAAMI | Maximum diameter measured at the base. |
| Shoulder Diameter | N/A | N/A | Straight walled cartridge; no shoulder. |
| Neck Diameter | 0.423 in (10.74 mm) | SAAMI | Maximum external diameter at the case mouth. |
| Base Diameter | 0.424 in (10.77 mm) | SAAMI | Measured just above the extractor groove. |
| Case Capacity | 19.3 gr H2O | Industry Standard | Varies slightly based on brass manufacturer and wall thickness. |
| Maximum Pressure | 35,000 psi | SAAMI | C.I.P. maximum is 225 MPa (approximately 32,633 psi). |
Understanding The .40 S&W Dimensions
- Bullet Diameter: The measurement across the widest point of the bullet. For the .40 S&W, this is specified as 0.400 inches. This dimension ensures the projectile seals properly within the barrel rifling to trap expanding gases and generate velocity while providing a larger frontal area than a 9mm projectile.
- Case Length: The length of the empty brass cylinder from the base to the case mouth, maxing out at 0.850 inches. This is a critical dimension because the .40 S&W headspaces on the case mouth.
- Overall Cartridge Length (OAL): The total length of the fully assembled round from the base to the tip of the bullet, strictly capped at 1.135 inches. OAL directly influences whether a cartridge will fit into a box magazine and feed properly. This specific length allows the .40 S&W to fit into grip frames originally designed for the 9mm Luger.
- Rim Diameter: The diameter of the flange at the very bottom of the case measuring 0.424 inches. The firearm extractor hooks onto this rim to pull the spent casing out of the chamber after firing.
- Case Diameter: The width of the cartridge body. The .40 S&W is an essentially straight walled case, measuring 0.424 inches at the base and 0.423 inches at the neck.
- Case Capacity: Measured in grains of water (gr H2O), this represents the internal volume of the empty case. Averaging 19.3 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.
.40 S&W Cartridge Dimensions In Inches And Millimeters
For engineers, reloaders, and international shooters, below are the primary .40 S&W measurements converted accurately between imperial and metric systems.
| Dimension | Inches (SAAMI Max) | Millimeters (Equivalent) |
| Bullet Diameter | 0.400 in | 10.16 mm |
| Case Length | 0.850 in | 21.59 mm |
| Overall Length | 1.135 in | 28.83 mm |
| Rim Diameter | 0.424 in | 10.77 mm |
| Base Diameter | 0.424 in | 10.77 mm |
| Neck Diameter | 0.423 in | 10.74 mm |
.40 S&W Case Dimensions
The .40 S&W is defined by a rimless, straight walled case. The official maximum case length is 0.850 inches (21.59 mm), with a nominal trim to length for reloaders sitting at 0.840 inches. The base diameter measures 0.424 inches, matching the rim diameter perfectly.
Because the .40 S&W operates at a relatively high pressure of 35,000 psi within a very compact volume, the brass case web must be manufactured strong enough to withstand the initial ignition sequence. Early generation pistols occasionally featured unsupported chambers at the feed ramp, which could cause weak brass cases to bulge or rupture near the web. Modern brass and modern fully supported chambers have largely eliminated this issue.
.40 S&W Bullet Diameter
The standardized maximum bullet diameter for the .40 S&W is 0.400 inches (10.16 mm). In practice, jacketed bullets typically measure exactly 0.400 inches to reduce friction, while lead or plated bullets might measure 0.401 inches to properly grip the rifling and prevent gas blow by.
The standard .40 S&W barrel features a groove diameter of 0.400 inches and a bore or land diameter of 0.390 inches. Firing a 0.400 inch bullet down a 0.400 inch groove diameter forces the bullet to engrave tightly into the rifling, creating spin and stabilizing the projectile.
.40 S&W Overall Length
The SAAMI maximum overall cartridge length (OAL) for the .40 S&W is 1.135 inches (28.83 mm). This number is a hard limit designed to guarantee that the cartridge will fit inside standard double stack magazines built for medium frame pistols.
When Smith & Wesson partnered with Winchester to develop the cartridge in 1990, the 1.135 inch OAL was specifically chosen so law enforcement agencies could adopt the new, more powerful caliber using handguns that were the exact same size and weight as their existing 9mm Luger service pistols.
.40 S&W Chamber And Cartridge Dimensions
The relationship between the .40 S&W cartridge and the firearm chamber is critical for reliable functionality. The .40 S&W cartridge headspaces on the case mouth.
This means the forward edge of the brass casing physically stops against a machined ledge inside the barrel chamber, preventing the cartridge from sliding too far forward into the bore. Because of this, the case mouth cannot be heavily roll crimped into the bullet. It must be taper crimped just enough to hold the bullet tight while leaving a distinct flat lip to engage the chamber ledge. Proper overall length and neck diameter are mandatory for this sequence to occur without a malfunction.
.40 S&W Dimensions vs Similar Cartridges
To understand the size profile of the .40 S&W, it is helpful to compare it against other popular semi automatic handgun cartridges.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Base Diameter | Maximum Pressure | Source |
| .40 S&W | 0.400 in | 0.850 in | 1.135 in | 0.424 in | 35,000 psi | SAAMI |
| 10mm Auto | 0.400 in | 0.992 in | 1.250 in | 0.425 in | 37,500 psi | SAAMI |
| 9mm Luger | 0.355 in | 0.754 in | 1.169 in | 0.391 in | 35,000 psi | SAAMI |
| .357 SIG | 0.355 in | 0.865 in | 1.140 in | 0.424 in | 40,000 psi | SAAMI |
| .45 ACP | 0.452 in | 0.898 in | 1.275 in | 0.476 in | 21,000 psi | SAAMI |
.40 S&W vs 10mm Auto Dimensions
The .40 S&W is a direct descendant of the 10mm Auto. Following the 1986 FBI Miami shootout, the FBI adopted the 10mm Auto but quickly realized the full power loads generated too much recoil and required grip frames that were too large for many agents. The .40 S&W was developed to solve this dimensional problem.
- Bullet Diameter: Both utilize identical 0.400 inch diameter bullets.
- Base and Rim: Both utilize the exact same 0.424 inch rim and base diameter.
- Case and Overall Length: The 10mm Auto utilizes a 0.992 inch case length and a 1.250 inch OAL. The .40 S&W shortened the case to 0.850 inches and the OAL to 1.135 inches.
- Interchangeability: Because the .40 S&W is simply a shortened 10mm Auto, you cannot fire a 10mm cartridge in a .40 S&W pistol. While a .40 S&W cartridge will physically fit in a 10mm chamber, it is unsafe to fire because the shorter cartridge cannot headspace correctly on the chamber ledge, relying solely on the extractor to hold it in place.
.40 S&W 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 dimensional specifications for the .40 S&W are functionally identical between the two bodies to ensure global compatibility, the pressure limits differ slightly in testing documentation. SAAMI lists the maximum average pressure for the .40 S&W at 35,000 psi, measured via conformal piezoelectric transducers. C.I.P. lists the maximum pressure at 225 MPa, which translates to approximately 32,633 psi. Ammunition loaded to SAAMI standard specs is completely safe in C.I.P. proofed handguns.
.40 S&W Bullet Weight And Dimensions
The .40 S&W is widely loaded in several common bullet weights, which drastically affect how the internal dimensions of the cartridge are managed.
- 155 grain: A lighter, faster bullet. Because it is physically shorter, it leaves ample internal case capacity for the powder charge.
- 165 grain: Often considered the ideal balance of velocity and mass for the caliber, offering excellent terminal ballistics while keeping pressures manageable.
- 180 grain: The original heavy bullet weight for the caliber. To maintain the strict 1.135 inch maximum overall length, this long bullet must be seated very deeply into the small brass case. This deep seating drastically reduces powder capacity, meaning slight variations in seating depth can cause dangerous pressure spikes.
Why .40 S&W Dimensions Matter
Understanding the specific .40 S&W dimensions is essential for several practical reasons.
- Frame Size Validation: The 1.135 inch OAL allows shooters to carry a larger caliber in a handgun with the exact same grip dimensions as a 9mm pistol, making it highly ergonomic for a wide variety of hand sizes.
- Bullet Setback: Because of the limited case capacity when using heavy 180 grain bullets, bullet setback is a major safety concern. If a cartridge is chambered repeatedly and the bullet is pushed deeper into the case, the reduced internal volume can push chamber pressures well beyond the 35,000 psi limit.
- Reloading Safety: The .40 S&W operates at high pressure in a small case. Reloaders must meticulously measure their powder charges and overall lengths, as the margin for error is significantly smaller than it is with low pressure cartridges like the .45 ACP.
Manufacturer Specifications vs Independent Measurements
If you use calipers to measure factory .40 S&W ammunition from companies like Speer, Federal, or Winchester, the numbers will rarely match the SAAMI specifications exactly.
SAAMI and C.I.P. publish maximum allowable dimensions to ensure safety and function across all platforms globally. Ammunition manufacturers produce their cases and load their cartridges slightly smaller than these maximums using negative tolerances to guarantee that their ammunition will chamber reliably. Therefore, measuring a factory cartridge and finding a case length of 0.842 inches or an OAL of 1.125 inches simply means the manufacturer built in a reliable dimensional tolerance margin.
Common Questions
What are the dimensions of the .40 S&W?
The key maximum dimensions are a bullet diameter of 0.400 inches, a case length of 0.850 inches, and an overall cartridge length of 1.135 inches.
What is the .40 S&W case length?
The maximum SAAMI case length is 0.850 inches (21.59 mm).
What is the .40 S&W overall length?
The maximum overall length (OAL) is 1.135 inches (28.83 mm).
What is the .40 S&W bullet diameter?
The standard bullet diameter is 0.400 inches.
What is the .40 S&W rim diameter?
The rim diameter measures 0.424 inches (10.77 mm).
What is the .40 S&W case diameter?
The case diameter at the base is 0.424 inches, maintaining a nearly straight wall up to the case mouth.
How does the .40 S&W compare with the 10mm Auto?
The .40 S&W is essentially a shortened version of the 10mm Auto. It uses the exact same 0.400 inch bullet and 0.424 inch base diameter, but features a shorter 0.850 inch case to fit inside smaller pistol frames.
What is the maximum overall length of the .40 S&W?
The absolute maximum allowed by SAAMI is 1.135 inches to guarantee compatibility with medium frame magazines.
What is the .40 S&W maximum pressure?
The SAAMI maximum average pressure is 35,000 psi.