This article is a historical and technical overview. It contains no load data, no charge weights, and no reloading instructions – identification and history only.
The Mix-Up That Confuses Even Experienced Reloaders
The names are almost identical. The bullets are not. 38 S&W and 38 Special share the same “38” designation, both trace to Smith & Wesson revolver history, and both fire a nominally .38-caliber bullet from a rimmed, straight-walled case. That surface-level resemblance is exactly why new reloaders, and more than a few experienced ones sorting through inherited ammunition boxes, mix them up – and this specific mix-up carries genuine safety consequences rather than being a purely academic naming curiosity. This article exists as a filter: a direct, dimension-first identification tool aimed at preventing one specific, well-documented mistake before it happens.
The stakes here are higher than a simple naming quirk because of who typically encounters this specific pair. Unlike several of the more obscure European service cartridges covered elsewhere in this series, 38 S&W and 38 Special are both genuinely common – the kind of cartridges an ordinary estate sale, gun show table, or inherited collection turns up regularly. That combination of frequent real-world encounter and a dangerously similar name is precisely the profile that produces actual mistakes rather than purely theoretical ones, which is why this article treats the dimensional comparison as safety-critical information rather than collector trivia.
History: Why 38 S&W Predates 38 Special by Decades
38 S&W is the older cartridge by a full generation, developed by Smith & Wesson in 1877 for the company’s 38 Single Action top-break revolver – more than two decades before 38 Special existed. Like many revolver cartridges of its era, the original 38 S&W loading used a heeled bullet, the bullet’s exposed portion matching the case’s outside diameter. Later production dropped the heeled design in favor of an internally seated bullet of reduced diameter, but Smith & Wesson kept the original “38” name even after the actual bullet diameter changed – a naming-convention quirk this series has documented repeatedly across other historical American cartridges, and one that matters directly here because the final bullet diameter that resulted is the single most important fact in this entire comparison.
38 S&W also carries a genuine tangle of alternate names worth knowing for identification purposes, since period boxes and headstamps rarely use a single consistent label. The cartridge appears variously as 38 S&W Short (to distinguish it from 38 Long Colt and 38 Special), 9×20mmR under metric designation, 38 Colt NP (New Police), and .38/200, the last name tracing directly to the British military’s heavier loading described below. Anyone encountering any of these names on a box, headstamp, or reference chart should recognize them as referring to the same underlying cartridge rather than assuming each represents something dimensionally distinct.
38 S&W went on to a genuinely significant military career far from its American origins. The British military adopted a heavier loading of the cartridge – a 200-grain bullet, giving rise to the alternate designation .38/200 – as its standard service revolver round from 1922 to 1963, chambered in Webley, Enfield, and Smith & Wesson-manufactured revolvers including the Webley Mk IV and the Enfield No. 2. That British service history produced a documented, specific identification hazard still relevant today: World War II-era Smith & Wesson Victory Model revolvers, originally manufactured to British .38/200 specification, have in some cases been reamed out by importers to accept 38 Special ammunition. Where that reaming has occurred, 38 Special rounds will physically chamber and fire – but because 38 Special operates at meaningfully higher pressure than the cartridge these revolvers were originally built around, fired cases in these reamed guns have been documented to occasionally bulge or split, a real, specific failure mode rather than a hypothetical caution.
38 Special, by contrast, was developed considerably later, in 1898, specifically for the new swing-out cylinder revolvers that were beginning to replace older top-break designs across the American market – the same mechanical transition this series has touched on in its coverage of period revolver evolution. Critically, 38 Special’s actual parent case is 38 Long Colt, not 38 S&W – a completely separate cartridge lineage despite the shared “38” name. This single fact is the structural key to understanding why this comparison matters as much as it does, and it deserves its own dedicated explanation.
The Dimensional Facts: Case Length, Rim, and Bullet Diameter Compared
| Specification | 38 S&W | 38 Special |
|---|---|---|
| Parent case | Independent design | 38 Long Colt |
| Case type | Rimmed, straight | Rimmed, straight |
| Bullet diameter | 0.361 in (9.2mm) | 0.357-0.358 in (9.1mm) |
| Case length | 0.775 in (19.7mm) | 1.155 in (29.3mm) |
| Overall length | approximately 1.56 in (39.6mm) | 1.550 in (39.4mm) |
| Rim diameter | Documented as slightly larger than 38 Special’s | 0.44 in (11.2mm) |
Dimensions given are nominal, drawn from published cartridge references. This table is for historical identification only and contains no current reloading data. Precise rim diameter figures for 38 S&W vary somewhat by manufacturer and era; verify with direct measurement rather than relying on a single published figure when the distinction matters for a specific firearm.
Case length alone tells most of the compatibility story here, and it tells it in an unusually clear-cut way compared to several other cartridge pairs this series has documented. 38 S&W’s case runs roughly 0.775 inch, while 38 Special’s case measures 1.155 inches – a difference of nearly four-tenths of an inch, large enough that 38 Special ammunition will not properly chamber in an unmodified firearm built for the shorter cartridge. This is a meaningfully larger, more obvious length gap than several of the more dangerous “close enough” pairings this series has documented elsewhere, which is part of why the real danger with this pair concentrates specifically in modified or reamed firearms rather than in accidental cross-chambering of unmodified guns.
Why Bullet Diameter Is the Detail Most People Miss
This is the fact the brief behind this article identified as the single most important one, and it deserves to be stated with complete clarity: 38 S&W and 38 Special do not fire the same diameter bullet. 38 S&W uses a .361-inch bullet. 38 Special – along with 357 Magnum, 38 Short Colt, and 38 Long Colt, all of which share compatible dimensions with each other despite their own case length differences – uses a .357 to .358-inch bullet. That is a real, measurable, four-thousandths-of-an-inch-or-more difference, and it is precisely the kind of detail that gets lost when a cartridge name promises a match the actual specification does not deliver.
This dimensional split explains something worth stating explicitly, because it corrects a common and reasonable-sounding assumption: many reloaders know that 38 Short Colt, 38 Long Colt, 38 Special, and 357 Magnum form a compatible, nesting family, where shorter cartridges in this specific lineage can generally be fired safely in firearms chambered for a longer relative within the same family. 38 S&W is not a member of that family at all, despite sharing the same “38” number. It is a structurally separate, independently developed cartridge with its own bullet diameter, and assuming it participates in the Colt-lineage compatibility pattern – simply because the name looks similar – is exactly the mistake this article exists to prevent. Where the Colt-lineage cartridges share genuine dimensional kinship going back to a common ancestor case, 38 S&W shares only a name.
The practical consequence for handloaders and collectors is direct: 38 S&W is never a safe or reliable substitute for 38 Special-family ammunition, and the reverse substitution is equally unreliable given the bullet diameter mismatch working in the opposite direction. This is not a one-directional, weaker-round-is-safe-in-the-stronger-gun pattern like several other pairings this series has documented. It is a genuine two-way dimensional incompatibility, on both case length and bullet diameter simultaneously – a distinction worth understanding precisely rather than assuming this pair follows the more familiar asymmetric-compatibility pattern common elsewhere in cartridge history.
Firearms Chambered in 38 S&W and How to Identify Them
38 S&W saw genuinely broad manufacturer adoption across more than eight decades of production, which matters directly for anyone encountering an unfamiliar revolver and trying to determine its correct chambering. Documented manufacturers producing revolvers chambered for 38 S&W include Colt, Harrington & Richardson, Hopkins & Allen, Iver Johnson, Ruger, and Smith & Wesson – a genuinely broad cross-section of American revolver manufacturing history, spanning from nineteenth-century top-break designs through to twentieth-century production. This breadth is exactly why “I found an old .38-caliber revolver” is not, on its own, sufficient information to determine safe ammunition without checking the specific chambering markings or measuring the chamber and barrel directly.
The British military connection adds a further, specific identification category worth knowing by name: Webley Mk IV revolvers, Enfield No. 2 revolvers, and Smith & Wesson Victory Model revolvers manufactured to British .38/200 contract specifications are all, functionally, 38 S&W-chambered firearms regardless of what a casual observer might assume from their general military-surplus appearance. Given the documented reaming practice described earlier, any Victory Model or British-contract revolver encountered on the secondary market deserves specific verification of its actual current chambering rather than an assumption based on its original manufacturing specification, since importer modification history is not always obvious from external inspection alone.
Domestic American production adds a second, equally important identification layer. Companies including Colt, Iver Johnson, and Hopkins & Allen produced 38 S&W-chambered pocket and top-break revolvers throughout the late nineteenth and early twentieth centuries for the American civilian market, well before the British military connection existed, meaning a 38 S&W-chambered firearm encountered today is just as likely to trace to purely domestic American production as to surplus British military stock. Neither origin story should be assumed without checking the specific markings or measurements on the individual firearm in question.
A Verification Checklist Before Sourcing Components
Anyone handling an unfamiliar 38-caliber revolver, or sourcing ammunition and components for a specifically identified 38 S&W firearm, should work through a direct verification sequence rather than relying on the cartridge name alone.
- Never assume “38-caliber” markings alone confirm compatibility between 38 S&W and any member of the 38 Special/357 Magnum family – measure or verify chamber dimensions directly rather than trusting a general caliber stamp.
- Check specifically for reamed WWII-era Victory Model or other British-contract revolvers before assuming original .38/200 specification still applies – importer modifications for 38 Special compatibility are documented and not always visibly obvious.
- Verify bullet diameter directly when sourcing components for either cartridge – the .361-inch versus .357/.358-inch distinction is the single most safety-relevant fact in this entire comparison, and it is easy to overlook when ordering components by cartridge name alone.
- Never attempt to fire 38 Special ammunition in an unmodified firearm marked for 38 S&W – the case length difference alone should prevent proper chambering, and forcing the issue risks damage or injury.
- Treat any firearm with ambiguous or worn caliber markings as unidentified until confirmed through direct measurement or inspection by a qualified gunsmith, rather than guessing based on general appearance or apparent age.
Practical Notes for the Modern Handloader
38 S&W’s rimmed, straight-walled case and broad historical manufacturer support make component sourcing more accessible than for many of the more obscure historical cartridges covered elsewhere in this series, though the critical .361-inch bullet diameter requirement means standard 38 Special or 357 Magnum-diameter bullets are not a correct substitute regardless of how similar the cartridge names appear. General case prep essentials apply throughout, and reloaders should verify bullet diameter specifications with particular care before ordering components, given how easy this specific dimensional mismatch is to overlook when shopping by cartridge name alone.
A single-stage press suits deliberate, verification-focused reloading for this cartridge, and reloaders unfamiliar with the case’s dimensional requirements benefit from a general guide on tuning a sizing die before working with period or reproduction brass, followed by the companion resource on tuning a bullet seating die once correctly diametered .361-inch bullets are sourced and confirmed. A reliable pistol priming tool rounds out the essential equipment list, and the overpressure verification discipline covered elsewhere on this site applies with particular relevance to reamed Victory Model and other modified British-contract revolvers, given the documented case bulging and splitting risk when 38 Special ammunition is fired in these firearms.
Readers researching where the correctly identified 38 Special side of this comparison actually leads have a full modern cluster available, including this series’ own coverage comparing 38 Special against 357 Magnum and 38 Special against 9mm Luger, along with dedicated 38 Special handloading guidance and a safe first 38 Special handload for reloaders starting fresh with the correctly identified, considerably more common modern cartridge.
The names will keep looking almost identical for as long as both cartridges exist, and no amount of article-writing changes that. What changes the outcome is checking the actual case length and, more importantly, the actual bullet diameter before assuming a “38” on a box or a barrel stamp means what a quick glance suggests it means.