Why do we call the .38 special a 38 and the .357 Magnum a .357?

Especially when both use the same diameter bullet?

Which is .357 if you didn't know.

Believe it or not this story starts back before the Civil War and the Colt Patterson pistol was first designed. The Colt Patterson was a .36 caliber cap and ball revolver using a round ball with a diameter of .365-.375. Depending on the bullet/ball mold used. The bullet/ball was slightly oversized to ensure a tight fit in both the cylinder and the barrel. Forcing the ball into the chamber would shave a thin slice of lead from the ball leaving a ring of lead behind.

As time progressed, Colt updated and modified his designs, giving us the Colt Walker, Dragoon, Navy and Army. The Walker, Dragoon and Army were in .44 caliber using a .445-.450 diameter ball, and the Navy using the same .365-.375 as the Patterson.

During the Civil War, cartridge firearm designs and conversions started to come into their own.

One of the most popular conversion designs converted the Colt Navy to a .38 caliber. However the .38 caliber wasn't for the bullet diameter, but the cartridge case diameter.

Many of the early .38 cartridges used a heeled bullet, similar to the .22 short, Long and Long Rifle of today, meaning the bullet had a narrow base that fit down inside the cartridge. And being a soft lead bullet, as it was forced through the forcing cone of the pistol, it engaged the rifling in the barrel better, giving it a better gas seal. The reason for the heeled bullet was it was difficult to crimp the cartridge into the bullet without a special and expensive tool, outside of an ammunition factory. Using heeled bullets, meant that users could reload their own cases in the field without many tools, besides a nail and a wooden dowel.

The original .38 Colt as it was known is now known as the .38 Colt Short As Colt came out with new and more robust designs, he lengthened the cylinder and introduced the .38 Colt Long as used in Colt M1877 Lightning. It was the US Army's use of the .38 Long Colt against the Philippine Moro's in their Colt M1892's which showed the cartridges inadequacies and which helped lead to the development of the .45 ACP.

However, as an attempt to salvage all of those .38 caliber firearms, Smith and Wesson developed from the .38 Colt Long, the .38 S&W Special in 1898.

So, that got us from the Colt Patterson to the .38 Special. But where did the .357 Magnum come in?

Well it starts with a man named Elmer Keith.

If you are big into shooting and you don't know who Elmer Keith is, you really need to box your ears and heigh thy butt to the library.

Elmer Keith is the FATHER of Magnums. Without his input, it is doubtful we wouldn't have the .357 Magnum, the .44 Magnum and many other things such as bullet designs, and the various types of reloading powders.

But in 1934, at the urging of Elmer Keith with Phil Sharpe, Douglas Wesson of Smith & Wesson, designed the .357 Magnum.

It still used the same .357 diameter bullet and the same .38 diameter case, however it was longer than it's parent case the .38 Special by 3.2 mm so it cannot be loaded in a .38 Special chambered firearm.

So there you have it. A brief primer on why the .38 special and the .357 Magnum both use the same diameter bullet.

And as a safety note, while you can in some .38 Special firearms, chamber the British .38/200 also known as the .38 S&W it is extremely unsafe to do so as the .38 S&W uses a .361 diameter bullet and the chamber pressures would be extremely unsafe to do so. However a firearm chambered for .38 S&W can safely chamber and fire .38 Colt Long and .38 Colt Short. Just not very accurately.  NOTE: I said SAFELY, this means you CANNOT fire the .38 Special from a .38 S&W firearm SAFELY.  It has to do with how fast the propellant burns and the pressure curves.  .38 Special develops too much pressure too fast, for the alloys of most available .38 S&W firearms.  Remember, everytime you fire a firearm, the pressure makes the chamber expand just a tiny bit.  then it shrinks back down.  The .38 special's pressure curve is too fast for the older .38 S&W chambered firearms metallurgy.  And while you might be able to fire a dozen or so cylinder fulls of .38 Specials, each time you do, you are forcing the chambers a little bit more out of spec.  Until one day you pull the trigger and the cylinder becomes a small hand grenade in your hand.  Think of an old Webley MK VI with a shaved cylinder to use .45 ACP's.  You can use low pressure low velocity .45 ACP ammunition in it.  But if you load a high velocity round in it, you have just destroyed your cylinder if not the whole firearm and possibly your hand or eyes.

And remember this, Your Mileage May Very and don't take what I write here as gospel. Be sure you have any older firearm checked by a competent gunsmith to be sure it is safe to fire ANY ammunition out of.

I make no claim to be an “Expert”, just a very talented amateur.