What is caliber, really?

[Kalos]

For as long as I can remember, I was given to believe that the caliber of a particular ammunition referred to the diameter of the projectile, generally in decimal inches--hence, a .22 would be .22" in dia, a 9mm would be, well, 9mm, a .50 would be half an inch, and so on.

Then, I happened to fire a friend's gun, and got hooked. So I started learning more about firearms, and came to an interesting anomaly--you can fire .38 spl rounds in a .357 mag revo. Now, if a .357 is .357" and a .38 is .38", you'd not be able to fit a .38 round into the chamber of a .357 and a .357 would fall right through the chamber of a .38. (Never mind, for now, that pesky rim.) After asking about, I find out that a .38 isn't .38, it's .357". Then I find out that a .45 isn't .45, it's .454. I had a table listing these things, but dunno where it's off to--but the point is still there. Whatever the caliber of a round is referring to, it's obviously not the size of the bullet.

So what is it? Or is there anything at all--do the numbers just get slapped on there willy-nilly? I'm rather curious.

 

[Keith]

There's different reasons for those variations. I think some of those calibers (.38 and .44) started out as "heeled" bullets that overlapped the brass (like a .22) and were originally the specified diameter. They later reduced the bullet size, but kept the nomenclature.
If you measure a .38 or .44 brass, it's close to .38 or .44. Only the bullet size was reduced slightly.

In other cases; like various .45's actually being .452 or .454. I think it was just "close enough".


Keith

 

[Drifting Fate]

"Caliber" is the bore diameter from land to land. Except for the British in the old days, which was groove to groove.

Now, don't confuse caliber with a cartridge designation. Typically, things would be rounded up, just like an engine displacement. For example, a 750cc motorcycle probably is really something like 746cc.

Also, when you have different cartridges of the same caliber, you have to do something to designate the difference. You can use names or numbers. Like, .44 Special vs. .44 Magnum. Or, .38 Special vs. .357 Magnum.

And, sometimes, things are going to be close. The .45 ACP is .452, the .45 LC is .454, but, they are different cartridges, and who wants to bother with three numbers when they can use two, right? So, they rounded off. Well, that was the idea at the time, at least.

History plays a part, too. First, there was the .36 cap and ball revolvers (black powder), then came the cartridges, but they wanted to distinguish the two, so they called it a .38 (close enough.) Then, they magnumized the .38, and used the true bore diameter that everything already had of .357.

Confused yet?

Caliber is bore diameter, and the name of the cartiridge is going to give you the rough measurment, but they were never meant to be exact designations.

 

[caz223]

The engine displacement example is also a very good one.
I was beaten to it.
It's also like the roman chariot example on why the modern wheelbase is the width that it is currently.

 

[Oracle]

A lot of this stuff has been standardized now. .45 ACP guns usually have a .451 - .452 bore, as do modern .45 Colt firearms. .44 Special and .44 Magnum are actually .429, closer to .43 caliber than to .44. .38 Special and .357 Magnum are both .357. 9mm is very close to them in diameter, at .355. Both the .357 Magnum and .44 Magnum are basically just hotloads of the .38 and .44 Special, but use longer cases that can contain more powder and will only fit in guns that are designed to use the longer cases, thusly the more powerful ammunition cannot be used in older guns that aren't as strong.

A "heeled" bullet is a bullet that is the same diameter of the cartridge case it is loaded in. The part of the bullet that is loaded in the case is slightly smaller than the case itself, while the rest of the bullet is the same diameter as the case. The only cartridges that use heeled bullets that are still in use are the .22 rimfire cartridges, to my knowledge.

 

[Mike Irwin]

Kalos,

The best way to think of the caliber is that it's an approximation, and can be driven by history or by marketing concerns.

A good example of history driving the naming of a round is the .44 Spl. or .44 Magnum.

As has been pointed out, those rounds are actually closer to .43 caliber. But, WAY WAY WAY back in time, .44 caliber rounds actually used .44 caliber bullets when they were loaded with heeled bullets, which Oracle describes. Heeled bullets are the diameter of the outside of the case mouth.

Starting in the 1870s, manufacturers began making the bullets the diameter of the inside of the case mouth. The bullets were easier to make, and bullet lubrication problems were greatly eased.

That's when the .38 bullet dropped down to .357, the .44 dropped down to .357, etc.


Then we have marketing concerns. A few years ago Sig and Federal brought out a round called the .357 Sig, for use in semi-auto pistols. The bullet is actually 9mm, which is closer to .355 diameter.

Sig's purpose for the round, though, was to capture a part of the police market that had stayed with revolvers firing .357 Magnum cartridges using 125-gr. bullets.

Sig named the round as they did, used a 125-gr. bullet, and loaded it to the same velocity range as the .357 Mag. cartridge they were hoping to replace.

 

[Kalos]

The heeled bullet thing does make quite a bit of sense--as does the marketing ploy side of it, of course. I guess I'll just stick this in the 'stuff my teachers forgot to tell me in school' file--well, perhaps closer to 'popular un-wisdom,' at least.

 

[BluesBear]

A good example is the old .41 Long Colt. As it was originally loaded for the Colt 1877 DA Revolver (aka The Thunderer) it had a outside lubricated bullet of .401. In later loadings for the Colt New Model Army it had a inside bullet diameter of .386. Since there were still a large number of older revolvers still in use the .386 bullet had a hollow base to help it the larger cylinder throat and bores of the older guns.

The .38/40 WCF also used a inside lubricated bullet diameter of .401. In this case the 38 stood for the weight in grains of black powder and 40 referred to the bullet diameter.

 

[Henry Bowman]

Welcome to THR, Kalos. As you can see -- ask a simple question, get a thorough answer! No question is too dumb or too esoteric for this group.

 

[Mike Irwin]

"The .38/40 WCF also used a inside lubricated bullet diameter of .401. In this case the 38 stood for the weight in grains of black powder and 40 referred to the bullet diameter."

Blues, sorry, but that's incorrect.

Standard cartridge nomenclature that developed in the 1870s for many American rounds used 2, 3, or sometimes even 4 sets of numbers to identify the cartridge.

The first set of numbers was always the nominal caliber, in this case, .38

The second set was always the charge weight in grains (normally black powder, but there were exceptions), in this case 40 grains.

A third set of numbers, mainly used with rifle cartridges, showed the bullet weight in grains (such as .45-70-405).

And finally, a fourth set, used only for a few rifle cartridges such as Sharps rounds, gave the case length in inches. This could be important because some companies offered rounds of the same caliber and bullet weight, with the same charge, but in straight cased and bottle necked versions. The bottle necks were shorter than the straight cases.

You'll occasionally see a rifle marked with a case length. The case length marking apparently fell by the wayside fairly quickly in favor of BN (bottle neck), which, as long as you've got the caliber and charge weight, gives you the information that you need.

I mentioned several exceptions to the second number being the charge weight in grains of black powder.

To the best of my knowledge, there were three, and they are all "transitional" cartridges, meaning that they were introduced just as smokeless powder was kicking off.

The .30-40 Krag, or .30 US Government, was the first so named.

Next, in 1895, came the .30-30 and .25-25 Winchester rounds.

And there that practice ended, more than likely because so many different kinds of smokeless powder were being developed that the second number simply didn't mean anything anymore because the charge weights were varying so much. There could be as much as a 5 grain difference in loads between say Pyro. No. 2 and Military Rifle 8. Both gave the same performance, but you can see the problem.

 

[Detachment Charlie]

Now, let's totally fog the issue with a discussion of calibers as in naval rifles.
As always, there's the right way, the wrong way and the Navy way.

 

[Mike Irwin]

Charlie, you mean 5"/38 caliber, or 16"/50 caliber?

Easy. The second number is the barrel length, in calibers.

You multiply it by the first number to get the total barrel length.

5"x38 = 190 inches, or 15.83 feet.

16x50 = 800 inches, or 66.6 feet.

 

[BluesBear]

Sorry Mike Irwin, but you need to do some homework.

It is true that for almost all of the old 19th century cartridges the first number was approximate bullet diameter followed by charge weight. Notice I said "almost" as the .38-40 (aka .38WCF) is the most notable (if not the only) exception.

The original Winchester load had a .401 180 grain inside lubricated bullet over 38 grains of black powder.

I guess they should have called it a .40-38 or a .40WCF but for some reason they didn't.

As I recall Jeff Cooper used the 180 grain soft point bullet made for the .38-40 in the original loads for the Bren Ten.

 

[Ky Larry]

Don't forget that some of the black powder loads used a three number system. For example the Government load for the Sharps was the .47-70-405.
.45 cal bullet
70 grains of black powder
405 grain bullet weight.

 

[Mike Irwin]

Blues,

I'd like to see your reference sources on that, as nothing I've got in my collection confirms what you're saying, but looking back through this you may be on to something.

I'm not, however, going to sacrifice one of my ca. 1877 .38-40 rounds to science.

As for homework, come on over for a study session. I've got close to 30 volumns on metallic cartridge development and history, and nearly 450 examples in my collection.

 

[Mike Irwin]

Ky,

Already covered that, along with the occasionally used 4th number -- case length.

 

[CMcDermott]

Wait a minute - the 44 WCF, 38 WCF and 32 WCF were ALWAYS incorrect for their size, none of these cartridges is based on an earlier case, and when Marlin mutated them into the 44-40, 38-40 and 32-20 it was still a purely marketing based naming decision. They could have kept the winchester names, but didn't want "WCF" on a Marlin product - kinda like "32 Colt Police" is really a 32 S&W Long with a SWC bullet.

Remember the "32" WCF uses a .312" diameter bullet, (same as a 303 British), the "38" WCF uses a .401" diameter bullet, same as modern 10mm and 40 S&W, and the "44" WCF used a .427" diameter bullet, but most modern examples have changed to the 44 Russian/Special/Magnum size of .429" diamater (one less easy to confuse barrel size, so the .427 for the 44 WCF went away). None of these cartridges ever had the bullet diameter match the name of the cartridge - and Winchester never gave a reason for why, so it was lost to history. All of these cartridges are pre-SAAMI standardization, and as Marlin used slightly different shoulders & neck lengths you can get mis-matches when trying to reload your cases for different original guns.

 

[BluesBear]

Mike,

I have been doing my homework for over 40 years now. Right now all of my reference books as well as all of my magazine back issues are in a storage building several hours drive from me. I have read numerous articlles over the last 40 years that all tell this story, but to make it easy I suggest you start with Cartridges of the World.

 

[Jim Watson]

I'm not a cartridge collector or ammunition expert or anything like, but the 1896 Colt catalog (reprint in an old Gun Digest) downstairs says, next to an illustration of a Lightning rifle and on and under the illustration of one of its cartridges:

Colt Magazine Rifle
Calibre .38
40 grains of powder

Greener, 1910, shows the 38 grain powder charge for .38 Winchester. I wonder when the change was made from folded head to the early solid head case we now call "baloon head" was made? That might well steal two grains of capacity.

As best as I can tell, the .38 WCF round was apparently not known as the .38-40 until Marlin came out with it and as has been said, didn't want to put "WCF" on a Marlin barrel.

I don't know anything in favor of "reversed" nomenclature for .38 WCF.

 

[Mike Irwin]

"but to make it easy I suggest you start with Cartridges of the World."

Duh. That's a given. Which of my editions would you like me to check? 2, 4, 5 or 7? 2, 4, and 5 are virtually verbatim, given that Cowboy Action shooting hadn't given the .38-40 the "kick in the popularity pants" that it would receive by the time the 7th edition came out in the mid 1990s.

Any way you look at it, though, Cartridges of the World says precious little about the origins of the round, gives its bullet diameter, and nothing at all about the original black powder loading.

Thinking about this even more, it is conceivable that the original loading was 40 grains of black powder, depending on the granulation chosen for the original loads, and that the .38 nomenclature was chosen because it was familiar to shooters whereas a .40 caliber would be less so.

The 1896 Colt catalog reprint seems to give that some creedence.

I've got a reprint of a Marlin catalog from around 1903, if I can find it. My 1904 DWM catalog is in the basement, but I don't think it's going to be of much help, unfortunately.

 

[BluesBear]

Had to take the teenage daughter to the Lynnwood library tonight and they have a reference copy of Cartridges Of The World 9th Edition ©2000

“Historical Notes The .38-40 was Developed by Winchester as a companion cartridge to its .44-40 and introduced in 1874. It is based on the .44-40 case necked-down to what is actually 40-caliber (0.401-inch). It was originally a blackpowder cartridge chambered in the Winchester Model 73 lever action. About 1878, Colt began chambering revolvers for it. I t was later offered in the Remington Model 141/2 pump-action, Winchester 92 and Marlin 94 lever actions, plus a number of single shot rifles. No rifles have been chambered for the .38-40 since 1937. Winchester loaded a slightly different version especially for the Colt Lightning magazine rifle, headstamped .38 C.L.M.R. Another version was loaded with the same 180-grain bullet as the .38 Winchester, but with 40-grains of blackpowder instead of Winchester’s standard load of 38 grains and was headstamped .38-40 instead of .38 W.C.F. This raises the intriguing possibility that the name we now use, .38-40, came from 38 grains of blackpowder and a .40 caliber bore.â€


>>>>>> the .44-40 case necked-down to what is actually 40-caliber <<<<<
>>>>>> Winchester’s standard load of 38 grains <<<<<<


And I am sure that if anyone wanted to take the time to look back through the various magazine articles written about .38-40 guns and ammunition over the years you will see that Michael McPherson & I are not the only 2 people on the planet that are aware of these facts. Just ask some of the CAS/SASS guys and gals.

Now this I all I am gonna say on this subject. You'll need to find someone else if you want to continue this pissing contest.

 

[Waitone]

I'm seriously outclassed.

<Tips his hat, bows at the waist, and humbly departs the room>

 

[Mike Irwin]

<Scratches head...>


Not sure why you viewed this as a "pissing contest," Blues Bear.

I certainly didn't.

Stick it back in your pants and chill the hell out.