The exact .38 Special bullet diameter is 0.357 inches, which converts to 9.07 millimeters. While .38 Special ammunition is available with different bullet weights, the cartridge’s nominal projectile diameter remains exactly the same across all factory loads. This measurement refers specifically to the width of the bullet itself, which differs from the internal dimensions of the barrel. Specifically, a standard .38 Special firearm utilizes a narrower bore diameter of 0.346 inches and a groove diameter of 0.355 inches to ensure a tight gas seal upon firing.
.38 Special Bullet Diameter
| Specification | .38 Special |
| Nominal Bullet Diameter | 0.357 inches |
| Bullet Diameter In Inches | 0.357″ |
| Bullet Diameter In Millimeters | 9.07 mm |
| Groove Diameter | 0.355 inches |
| Bore Diameter | 0.346 inches |
| Typical Bullet Weights | 110 gr to 158 gr |
| Case Length | 1.155 inches |
| Overall Cartridge Length | 1.550 inches |
| Maximum Pressure | 17,000 PSI |
What Is The .38 Special Bullet Diameter?
The .38 Special bullet diameter is the physical width of the unfired projectile seated in the cartridge case. Introduced in 1898 by Smith & Wesson, the cartridge evolved from the earlier .38 Long Colt. Despite its name containing “.38,” the bullet was intentionally redesigned to measure 0.357 inches across to provide superior accuracy and stopping power.
.38 Special Bullet Diameter In Inches
According to the official Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) specifications, the .38 Special bullet diameter in inches is standard at 0.357 inches. While manufacturing tolerances allow for very minor variations depending on whether the ammunition features a jacketed hollow point or a traditional unjacketed lead wadcutter, 0.357″ is the exact nominal measurement for factory loads.
.38 Special Bullet Diameter In Millimeters
For those using metric measurements, the .38 Special bullet diameter in mm is 9.07 mm. Because 1 inch equals 25.4 millimeters, multiplying a 0.357-inch bullet by 25.4 yields exactly 9.0678 mm, which cleanly rounds to 9.07 mm.
.38 Special Bullet vs Bore Diameter
A common point of confusion is the difference between the bullet’s width and the barrel’s internal dimensions. The .38 Special bore diameter is 0.346 inches. The bore diameter measures the distance directly across the “lands” (the raised portions of the rifling inside the barrel). The unfired .38 Special projectile diameter (0.357″) is deliberately wider than the bore so the rifling can firmly bite into the bullet, imparting the stabilizing spin required for accuracy.
.38 Special Groove Diameter
The .38 Special groove diameter measures 0.355 inches. The groove diameter measures the distance across the deepest cuts inside the rifled barrel. When the 0.357-inch bullet is fired, it swages (squeezes) down slightly to completely fill the 0.355-inch grooves. This creates a tight pressure seal that traps the expanding powder gases directly behind the bullet, preventing velocity loss.
.38 Special Bullet Weights
While the cartridge diameter is fixed, you can select vastly different projectile masses depending on your application. The .38 Special bullet weight typically ranges from lightweight 110-grain defensive loads up to traditional 158-grain lead round nose or semi-wadcutter rounds. Changing the weight alters the bullet’s length, recoil impulse, and trajectory, but the diameter remains fixed at 0.357 inches.
Bullet Diameter vs Other Cartridges
Shooters must be careful when comparing caliber names, as historical cartridge names frequently do not match the physical measurement. Here is how the .38 Special compares to other rounds:
| Cartridge | Bullet Diameter | Diameter In mm |
| .38 Special | 0.357″ | 9.07 mm |
| .357 Magnum | 0.357″ | 9.07 mm |
| .350 Legend | 0.357″ | 9.07 mm |
| .357 SIG | 0.355″ | 9.02 mm |
| 9mm Luger | 0.355″ | 9.02 mm |
| .380 ACP | 0.355″ | 9.02 mm |
Notice that despite being called “.38 Special,” its actual bullet diameter is 0.357 inches—making it completely identical in projectile size to the .357 Magnum, even though their cases are entirely different lengths.
Bullet Weight
Ammunition manufacturers produce several specialized loads for the .38 Special, ranging from target shooting wadcutters to +P defensive rounds.
| Bullet Weight | Example Load | Bullet Type | Advertised Velocity |
| 110 grain | Hornady Critical Defense +P | FTX | 1,090 fps |
| 125 grain | Speer Gold Dot +P | JHP | 945 fps |
| 130 grain | Winchester USA | FMJ | 800 fps |
| 158 grain | Remington Lead Round Nose | LRN | 755 fps |
| 148 grain | Federal Target | Lead Wadcutter | 710 fps |
Velocities represent typical factory test barrel data, generally from a 4-inch barrel.
Dimensions
To understand how the cartridge fits into standard revolver cylinders, here are the complete SAAMI-verified .38 Special dimensions:
| Dimension | Measurement |
| Bullet Diameter | 0.357″ |
| Groove Diameter | 0.355″ |
| Bore Diameter | 0.346″ |
| Case Length | 1.155 inches |
| Overall Length | 1.550 inches |
| Base Diameter | 0.379 inches |
| Neck Diameter | 0.379 inches |
| Rim Diameter | 0.440 inches |
| Maximum Pressure (SAAMI) | 17,000 PSI (20,000 PSI for +P) |
.38 Special vs .357 Magnum
Because both cartridges share an exact 0.357-inch bullet diameter, many shooters frequently compare the .38 Special and .357 Magnum.
Despite sharing a bullet diameter, they are built for entirely different performance levels:
- Case Length: The .38 Special case length is 1.155 inches, which is intentionally shorter than the .357 Magnum case (1.290 inches). This ensures a high-pressure .357 Magnum round cannot physically fit into an older or weaker firearm chambered exclusively for .38 Special.
- Pressure and Velocity: Standard .38 Special operates at a mild 17,000 PSI, generating modest velocities around 750–800 fps. The .357 Magnum operates at 35,000 PSI, pushing the same 0.357-inch bullet at speeds exceeding 1,200 to 1,400 fps.
You can safely shoot .38 Special ammunition in any modern .357 Magnum firearm, but you should never attempt to fire .357 Magnum rounds out of a gun rated only for .38 Special.
.38 Special Bullet Diameter: Exact Measurement
The exact .38 Special bullet diameter is 0.357 inches, or 9.07 millimeters.
While the actual projectile measures 0.357 inches across, it is pushed through a barrel with a 0.346-inch bore diameter and a 0.355-inch groove diameter. This intentional sizing ensures the bullet squeezes tightly into the barrel’s rifling grooves. This physical engagement creates a reliable gas seal behind the projectile, preventing the 17,000 PSI of expanding gases from blowing past the bullet while stabilizing it for accurate target placement.
FAQs
What is the bullet diameter of .38 Special?
The nominal bullet diameter is 0.357 inches.
What is .38 Special bullet diameter in mm?
In metric measurements, the diameter translates to 9.07 mm.
Is .38 Special actually .38 inches?
No. Despite the name, the actual bullet measures 0.357 inches in diameter.
Is .38 Special the same diameter as .357 Magnum?
Yes. Both cartridges utilize the exact same 0.357-inch bullet diameter.
What is the bore diameter of .38 Special?
The barrel’s internal bore diameter (measured land-to-land) is 0.346 inches.
What is the groove diameter of .38 Special?
The barrel’s internal groove diameter (measured groove-to-groove) is 0.355 inches.
What bullet weights are available for .38 Special?
Factory loads typically range from 110-grain defensive rounds up to 158-grain lead loads and 148-grain target wadcutters.
What is the case diameter of .38 Special?
The case is straight-walled, measuring 0.379 inches across the base and neck.
How does .38 Special bullet diameter compare with 9mm?
A standard 9mm Luger bullet measures 0.355 inches, making the .38 Special (0.357 inches) fractionally wider by two-thousandths of an inch.