38 Special vs 357 Magnum: Same Bullet, Twice the Pressure

38 Special and 357 Magnum fire the same bullet diameter; the Magnum case is longer and its pressure ceiling is about twice as high.

Last updated: September 21, 2026 · Originally published September 9, 2026

.38 Special and .357 Magnum are the same bullet in the same-diameter case, 0.135 inches apart in length — and one of them is loaded to slightly more than twice the pressure of the other. That length difference is not a design accident. It is a safety interlock, and it only works in one direction.

What actually differs between .38 Special and .357 Magnum?

Read the diameter rows and then the pressure row. Everything that governs whether a cartridge will physically enter a chamber is the same. The only dimension that differs is length, and the only performance figure that differs is pressure — by a factor of just over two.

One more thing the standard quietly tells you: .38 Special, .38 Special +P and .38 Special Match all share a single cartridge drawing and a single test barrel. SAAMI treats +P as a pressure level of the same cartridge, not a different one. And .38 Special’s own proof loads are listed as obsolete, with the instruction to use the +P proof loads instead.

Quick answers

What each cartridge actually does

Compare the two Speer Gold Dot Short Barrel loads, because they are the cleanest comparison available: same maker, same bullet weight, same 2-inch vented barrel, same product line. The .357 Magnum runs 990 fps and 294 ft-lb; the .38 Special +P runs 860 fps and 222 ft-lb. That is a 32 per cent energy advantage to the Magnum out of a snub-nosed revolver — real, but a long way short of what the pressure difference suggests, because a two-inch barrel gives the extra powder nowhere to work.

Now compare the same maker’s .357 loads at 2 inches and 8 inches: 294 ft-lb against 624. The barrel matters more than the headstamp.

A caution on cross-brand comparisons here. Federal publishes from 4-inch and 6-inch vented barrels, Hornady from 8-inch and 4-inch, Speer from 2-inch. Remington, Winchester and Underwood publish no barrel length at all. And SAAMI’s own vented reference barrels — 5.643 inches for .357, 5.631 for .38 — match none of them. There is no like-for-like table to be built from published figures, and anyone who shows you one has quietly assumed something.

The measurement that answers the question directly

One maker, Buffalo Bore, publishes velocities from named stock revolvers rather than test barrels, and states why: “We never use extra long laboratory barrels to produce our advertised velocities, which we feel is dishonest to the customer as those extra long barrels produce extra high velocities, which you cannot duplicate with stock revolvers in the real world.”

Their 158-grain .38 Special +P hard cast load is chronographed in eight revolvers — some chambered in .38 Special, some in .357 Magnum, since the ammunition is legal in both:

Look at the two matched pairs. At 1⅞ inches, the .38-chambered gun is 38 fps faster than the .357-chambered one. At 4 inches, 21 fps faster. Two pairs is not a study, and the guns differ in more ways than their chambering. But it is the only published data I could find that puts the same ammunition through both chambers, and it does not show the .357 chamber helping.

There is a plausible mechanical reason — the longer .357 chamber leaves a .38 Special bullet a longer unsupported jump before it reaches the rifling — and Buffalo Bore does not offer that explanation on the page. I am noting the pattern, not claiming the cause.

The same source is worth reading on why barrel length alone explains less than people assume: “Barrel length is not a stand-alone determiner of velocities and therefore energies. Factors such as barrel/cylinder gap, chamber dimensions, chamber throats, barrel throats, rifling depth and dimensions, rifling style or type, barrel material, bullet material and powder burn rate, etc., all have an impact on velocity achieved.” Their own tables bear it out: a 6-inch Colt Python produced less velocity than a 4-inch Smith & Wesson with one .357 load.

So which one should you buy?

The honest framing is not which cartridge wins, but which gun you own. A .357 Magnum revolver shoots both, so the cartridge question becomes a load question you can revisit any time. A .38 Special revolver shoots one of them, permanently.

Beyond that, the published figures support a few plain statements. The Magnum carries substantially more energy at every barrel length anyone publishes. The gap narrows sharply in a short barrel, where there is less room for the extra powder to do its work. And .38 Special ammunition is loaded across a wider range than most people realize — from 770 fps wadcutters to +P loads over 1,100 fps out of a 3-inch gun.

What nobody publishes is recoil, for either cartridge, from any maker — so the trade everyone actually feels is the one with no numbers attached to it.

What nobody publishes

• Recoil. No maker, either cartridge, any load. SAAMI’s standard contains no recoil specification.
• Ballistic coefficient. Absent from Federal, Hornady, Speer, Remington, Winchester and Buffalo Bore. One exception found: Underwood publishes .19 for one .357 load.
• Test barrel length — not published by Remington, Winchester or Underwood on any load in this set.
• Winchester product pages return “There is no ballistics data available at this time”; velocity for those loads exists only on the category listing.
• Where a load sits against the pressure ceiling. SAAMI publishes the limit; no maker publishes what its ammunition actually measures.

Where to go next

My .357 Magnum vs .44 Magnum comparison takes the argument up a size, 44 Magnum ammo covers the larger cartridge in full, and the caliber comparison chart shows how .357 inches sits against everything else. For revolver selection, see Guns and Gadgets Daily.

Sources

• ANSI/SAAMI Z299.3-2022 centerfire pistol and revolver standard — .357 Magnum and .38 Special cartridge and chamber drawings, velocity and pressure tables, solid and vented test barrel drawings, proof load tables
• SAAMI, Generally Accepted Firearms and Ammunition Interchangeability, 8 October 2021
• Federal product pages AE357A, P357HS1, P357SHC1, AE38K, AE38B and P38HS1
• Hornady 90500, 92755, 90311 and 90300; Speer Gold Dot Short Barrel 23917GD and 23921GD
• Buffalo Bore items 19G, 19K, 20A, 20D, 20F and 20H, and its published article on velocity versus barrel length
• Remington 22233 and 22297; Winchester Super-X and Defender listings; Underwood Xtreme Penetrator and Xtreme Defender

James Nicholas

NFA Firearms Manufacturer and Professional Gunsmith. The XDMAN has a talent for taking complex firearms subject matter and breaking it down into an easy-to-understand format that all experience levels can relate to. James is an 07/02 NFA Firearms Manufacturer, a Professional Gunsmith with over 20 years of experience, and a Firearms Writer, Photographer and Firearms Expert. Connect with him on Instagram, X, and Facebook as @therealxdman.

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