Definition
.38 caliber designates a family of firearm cartridges whose projectile diameter is approximately 0.38 inches (9.65 mm). The designation is used primarily in the United States and refers to the nominal bore size rather than an exact measurement; actual bullet diameters within the .38 caliber group typically range from about 0.357 inches to 0.388 inches, depending on the specific cartridge design.
Overview
The .38 caliber classification encompasses several distinct cartridges developed for revolvers, semi‑automatic pistols, and rifles. Prominent examples include the .38 Short Colt (introduced in the mid‑19th century), the .38 Long Colt, the .38 Special (introduced by Smith & Wesson in 1898), the .38 Super (developed in the 1920s), and more modern variants such as the .38 Special +P and .38 Special +P+. These cartridges have been employed for law enforcement, personal defense, target shooting, and, historically, for military sidearms. Over time, the .38 Special became especially associated with police service weapons in the United States throughout much of the 20th century, while the .38 Super found popularity in competitive shooting disciplines such as International Practical Shooting Confederation (IPSC) and International Defensive Pistol Association (IDPA) matches.
Etymology/Origin
The “.38” component of the name derives from a historical measurement convention in which firearms were described by the approximate diameter of the projectile in inches, expressed with a leading decimal point. Early American cartridge naming often referenced the bore size of earlier muzzle‑loading firearms, even though subsequent smokeless‑powder cartridges frequently employed slightly smaller bullet diameters for improved performance and compatibility. The term “caliber” itself originates from the French calibre, meaning “measure,” and entered English firearm terminology in the 16th century.
Characteristics
| Feature | Typical Values (for .38 Special, as representative) |
|---|---|
| Bullet diameter | 0.357 in (9.07 mm) |
| Case length | 1.155 in (29.3 mm) |
| Overall length | 1.550 in (39.4 mm) |
| Standard pressure | ≤ 17,000 psi (≈ 117 MPa) |
| +P pressure | ≤ 20,000 psi (≈ 138 MPa) |
| Common bullet weights | 110–158 gr (7.1–10.2 g) |
| Typical muzzle velocity (standard load) | 750–950 ft/s (230–290 m/s) |
| Typical muzzle energy (standard load) | 190–260 ft·lb (258–353 J) |
Note: Specific dimensions and performance figures vary among the different .38 caliber cartridges (e.g., .38 Super uses a 0.356‑in bullet and higher pressures, producing velocities above 1,250 ft/s).
Key characteristics of the .38 caliber family include:
- Semi‑rimmed or rimmed case design: Most .38 cartridges employ a rimmed case suitable for revolver chambers, although some (e.g., .38 Super) are semi‑rimmed for use in semi‑automatic pistols.
- Pressure considerations: Standard .38 Special loads are mild-pressure, allowing safe use in older, lower‑strength revolvers. Higher‑pressure +P and +P+ loadings require modern firearms rated for such pressures.
- Ballistic performance: Compared to larger-diameter cartridges such as .45 ACP, .38 caliber rounds generally offer higher velocity with reduced recoil, balancing controllability and stopping power.
- Interchangeability limits: While many revolvers chambered for .38 Special can safely fire .38 Short Colt and .38 Long Colt cartridges, the reverse is not true; likewise, .38 Super is not interchangeable with .38 Special due to dimensional and pressure differences.
Related Topics
- .38 Special – The most widely used .38 caliber cartridge, known for its longevity in law‑enforcement service.
- .38 Super – A higher‑pressure, semi‑automatic pistol cartridge derived from the .38 ACP case.
- .357 Magnum – A .38 Special–derived, lengthened cartridge offering substantially higher velocity and energy.
- Firearms calibers – The broader classification system for measuring projectile diameter across all small arms.
- Cartridge case design – Concepts such as rimmed, semi‑rimmed, and rimless cases that affect feeding mechanisms.
- Ballistics – The study of projectile motion, including internal, external, and terminal ballistic characteristics.
- Law enforcement sidearms – Historical and contemporary use of .38 caliber pistols in police forces.