What is going on with civilian gun calibers?

[Centurian52]

I've been interested in military history for as long as I can remember. That includes an interest in the weapons used by various armies over the ages. But I've rarely spared a thought for civilian weapons. Nevertheless I've gleaned a handful of things about civilian weapons over the years. I know that the US civilian gun market continues to use imperial units, stating calibers in inches (generally said aloud as hundredths of an inch, so a caliber of 0.22 inches would be said aloud as "twenty-two"). This contrasts with the US Military, which long ago grew enough sense to switch to metric, so military rifle calibers are stated in millimeters* (5.56mm).

I am often told that such and such military rifle caliber has a civilian equivalent. I've been told that the civilian equivalent of 5.56mm ammunition is 0.22. But there's a problem. The math doesn't work. The conversion factor between inches and millimeters is 25.4. Multiply by 25.4 to convert inches to millimeters. Divide by 25.4 to convert millimeters to inches. So if the military (metric) caliber is 5.56, then the civilian (imperial) caliber should be 0.2189. Ok, that's pretty close to 0.22 inches. Maybe they're just rounding up?

That's what I had assumed for years. And then the XM7/XM250 program gave us the new 6.8mm round. And the civilian equivalent of that is supposedly 0.277. But 6.8 divided by 25.4 is 0.2677. If they were rounding up that might justify calling it 0.27. But not 0.277. If you go the other way, and convert 0.277 inches to metric you get 7.036mm. So they're close, but the difference is more than a rounding error. So either they're measuring in two fundamentally different ways (perhaps the military is measuring the diameter of the round, while the civilian market is measuring the diameter of the inside of the barrel to the outside of the rifling?), or these rounds aren't "equivalent" at all, but two fundamentally different rounds. Perhaps someone who knows more about civilian firearms can enlighten me.

*Except 0.50 cal. That's the only US military caliber that's still stated in inches (that I can think of). Probably because it's been around for so long.

[Vacillator]

1 hour ago, Centurian52 said:

so a caliber of 0.22 inches would be said aloud as "twenty-two"

Going back a while, but in the UK airgun pellets were generally known as 'two two'.  Or 'one seven seven'.  But this doesn't seem to work for larger bullet stuff for some reason, like a 'thirty eight' for example.  We don't have many of those sloshing around in the UK of course, so the name is likely the US derivation.

2 hours ago, Centurian52 said:

0.50 cal. That's the only US military caliber that's still stated in inches

This is known as 'fifty cal' here, which I suppose goes with 'thirty eight'.  And your 'twenty two' rather than my 'two two'...

2 hours ago, Centurian52 said:

If they were rounding up

It might be a case of sloppy mathematics?  And by that I do not necessarily mean by the gun-wielding masses, obviously.

1 hour ago, Centurian52 said:

enough sense to switch to metric

Amen to that .

[Centurian52]

5 minutes ago, Vacillator said:

This is known as 'fifty cal' here

Same here. When saying it verbally you'd always say "fifty cal". But when typing it I always include the decimal point and leading zero. So I say "fifty cal", but I type "0.50 cal".

[Vacillator]

2 minutes ago, Centurian52 said:

I say "fifty cal", but I type "0.50 cal"

To avoid any possible confusion with the likes of a 50mm KwK 39 L/60? Anyway I'm sorry for distracting your focus...

[Centurian52]

14 minutes ago, Vacillator said:

To avoid any possible confusion with the likes of a 50mm KwK 39 L/60? Anyway I'm sorry for distracting your focus...

No. Just because it helps keep track of the actual size of the round. Typing 0.50 reminds me that the round is, in fact, 0.5 inches in diameter. That puts it on the same scale as any other caliber that's stated in imperial units. So I know at a glance that the bore of a 3 inch anti-tank gun has a diameter that is exactly six times larger than a 0.50 inch heavy machine gun. 

Keeping track of the scale is also helped by the fact that I have, by now, memorized a number of imperial to metric conversions. I know that a 0.30 caliber round is the same as a 7.62mm round, that a 0.50 caliber round is the same as a 12.7mm round, and that a 3 inch shell is the same as a 76.2mm shell. So if I see one of the common imperial calibers I can pretty quickly switch to thinking about it on a metric scale as well.

Edited September 24 by Centurian52

[Redwolf]

Americans and their units of measurement...

[Centurian52]

48 minutes ago, Redwolf said:

Americans and their units of measurement...

I did say the military had enough sense to switch to metric. Or at least the Army did. The US Air Force still uses feet to describe altitude (which irks me every time I hear it). And both the Air Force and the Navy apparently still describe distances in nautical miles, leaving me with absolutely no clue how far they're talking about.

Edit: Ok, 1 nautical mile is apparently...uhg...1.15078 miles, or 1.852 kilometers. There's no way I'm committing that to memory. Who's idea was nautical miles? I'll add their name to the hit list for if I ever get a time machine.

Edited September 24 by Centurian52

[Vacillator]

20 minutes ago, Centurian52 said:

I did say the military had enough sense to switch to metric. Or at least the Army did. The US Air Force still uses feet to describe altitude (which irks me every time I hear it). And both the Air Force and the Navy apparently still describe distances in nautical miles, leaving me with absolutely no clue how far they're talking about.

In the UK (before and after the fiasco aka Brexit), we use miles for road signs and pints for beer, but apart from some Luddites we use grams or kilograms for food.  We use degrees Celsius for temperature but a rearguard action using Fahrenheit is slowly receding into memory.

When it comes to buying fuel for our cars we switched to litres, but I think that was to make it seem cheaper when the gallon price got to £5 (it's still well over that).

I know my good friend @Warts 'n' all will want to comment on this.  Or maybe not.

[Redwolf]

2 hours ago, Centurian52 said:

I did say the military had enough sense to switch to metric. Or at least the Army did. The US Air Force still uses feet to describe altitude (which irks me every time I hear it). And both the Air Force and the Navy apparently still describe distances in nautical miles, leaving me with absolutely no clue how far they're talking about.

Edit: Ok, 1 nautical mile is apparently...uhg...1.15078 miles, or 1.852 kilometers. There's no way I'm committing that to memory. Who's idea was nautical miles? I'll add their name to the hit list for if I ever get a time machine.

The whole air traffic world, military and civilian, is set on nautical miles, feet, feet/min (ascending/descending) and similar nonsense.

That would have been one advantage if the Luftwaffe had prevailed... 

[Warts 'n' all]

8 hours ago, Vacillator said:

In the UK (before and after the fiasco aka Brexit), we use miles for road signs and pints for beer, but apart from some Luddites we use grams or kilograms for food.  We use degrees Celsius for temperature but a rearguard action using Fahrenheit is slowly receding into memory.

When it comes to buying fuel for our cars we switched to litres, but I think that was to make it seem cheaper when the gallon price got to £5 (it's still well over that).

I know my good friend @Warts 'n' all will want to comment on this.  Or maybe not.

Well given the invitation it would be rude not to comment. I have the weather page on Aunty Beeb's website set to Fahrenheit. I always talk about milk and beer in pints, although somewhat confusingly most bottled beer in the UK comes in 500ml bottles, whilst milk in our supermarkets is still sold in imperial containers. As for food I don't really care, although I do still talk about ham and stilton in terms such as "half a pound" or "a pound". As for petrol (or gas, as the girlfriend calls it) I don't care how it is sold, she's the driver. But, @Vacillator is probably right, I seem to remember them going over to litres just after it hit 5 quid a gallon.

Meanwhile, finding this Prussian milepost whilst playing something other than CM, made me smile.

 

[chuckdyke]

11 hours ago, Centurian52 said:

So if I see one of the common imperial calibers I can pretty quickly switch to thinking about it on a metric scale as well.

A 17 Pounder is a heck of a lot more powerful than a soviet 76.2 mm even if it is 76.2 mm too. I agree 17 pounds is far more effective if it travels at 3000ft/second, compared to 6.5 kg traveling at 680 m/sec. IMHO no need to convert one way or the other. Raise a beer Pony, Glass, Middy, Pot, Schooner or a Pint have your pick. Australia was very civilized before it became metric. On the horses you could bet two bob, your red-haired mate was called Blue. 

[Redwolf]

Gun sizes stated by shot weight ("25 pdr") is better than by diameter, since it expresses things in quadratic terms, making it more clear how much more it is.

Even better would be by kinetic energy. Shot weight still doesn't express what Chuck mentions.

[Centurian52]

3 minutes ago, Redwolf said:

Gun sizes stated by shot weight ("25 pdr") is better than by diameter, since it expresses things in quadratic terms, making it more clear how much more it is.

Even better would be by kinetic energy. Shot weight still doesn't express what Chuck mentions.

I'm not sure shot weight is any more useful than diameter.

For one thing, does every round fired by the 17pdr actually weight 17 pounds? Certainly its basic AP round does, since that's what the name was derived from. But what about the HE round? Or the later APDS round?

For AP rounds the mass is one part of the equation, but you still need the velocity to get the kinetic energy. And even then you need the area the energy would be spread over before you can actually start getting the penetration (assuming you have the necessary math skills, which I don't).

For HE rounds you generally go by the amount of explosive filler, normally measured in grams. Both the shot weight and the bore diameter are useful for giving you a rough idea of the ballpark amount of explosive power that the HE round probably has. But only a rough idea, since two HE rounds of the same caliber or weight might still have different amounts of explosive filler if one of them has to withstand higher chamber pressures (so has thicker shell walls, so has less room for explosive filler).

So if you actually want to know the performance of the ammunition, there's a lot more that needs to be accounted for anyway. But keeping track of where all the gun calibers fit on one scale does at least help to keep one variable under control.

[Halmbarte]

The most basic thing to understand about firearm ammunition names is that it's marketing 1st and accurately descriptive as a very distant 2nd. Besides just knowing (or looking up) you have absolutely no indication that the parent cartridge for .357 Magnum is actually a .357 bore diameter high pressure derivative of .38 Special. 

H

[ALBY]

@Centurian52 at the risk of hectoring you, I am somewhat suprised by your comments about civilians.  We are probably responsible for a lot of the caliber naming craziness.

5.56 NATO is basically a .223 caliber Varmit round.  A gun with a wylde chamber will fire both rounds. They are interchangeable.  The army didn’t develop it. Hunters did. 
 

7.62 NATO is .308 caliber which is the ballistic twin of 30-06, a popular big game round. 

when it comes to small arms, it’s been American civilians that have led the way in innovating our small arms and ammo. 6.8 Grendel, 300 win-mag, .338 lapua, 300 blackout/whisper… all innovated by civilians… Wildcat loaders and guys with machines who know what a thousandth of an inch is.  the army marksmanship unit sends a team to civilian 3 gun match’s to compete against the best.   They also host an awesome match at fort Benning.  Ronnie Barrett, a dude from Tennessee, figured out how to fit .50 cal in a sniper rifle. Mike Dillon, a guy who sells blue reloading press, devloped mini guns for the secret service.  Swarovski and Vortex optics developed scopes with 1-6 and 1-8 power for the shooting sports that are now used by elite units.   Larue Tactical in Texas developed all the quick change RTZ mounts for these optics.  3gun, USPSA, IPSC, IDPA…  We are a national asset that nobody really appreciates.  
 

 

Edited October 4 by ALBY
Punctuation and grammar

[ALBY]

On 9/25/2024 at 6:35 AM, Centurian52 said:

For AP rounds the mass is one part of the equation, but you still need the velocity to get the kinetic energy. 

For small arms,AP rounds usually have a steel core/penetrator.  But indeed, it is the velocity that cuts steel.  Even ball 556 will punch thru soft steel at 50 yards because it’s moving 3000fps.   Discarding sabots are often used to achieve high velocity for tank rounds.  I think tungsten or depleted uranium cores go into those. 

Edited October 4 by ALBY

[ALBY]

On 9/25/2024 at 8:46 AM, Halmbarte said:

Besides just knowing (or looking up) you have absolutely no indication that the parent cartridge for .357 Magnum is actually a .357 bore diameter high pressure derivative of .38 Special. 

H

.38 caliber = a bore dimension of .357

its where you measure the round. Old Timey stuff.

.38 caliber = 9mm as well 

[Centurian52]

1 hour ago, ALBY said:

@Centurian52 at the risk of hectoring you, I am somewhat suprised by your comments about civilians.  We are probably responsible for a lot of the caliber naming craziness.

5.56 NATO is basically a .223 caliber Varmit round.  A gun with a wylde chamber will fire both rounds. They are interchangeable.  The army didn’t develop it. Hunters did. 
 

7.62 NATO is .308 caliber which is the ballistic twin of 30-06, a popular big game round. 

when it comes to small arms, it’s been American civilians that have led the way in innovating our small arms and ammo. 6.8 Grendel, 300 win-mag, .338 lapua, 300 blackout/whisper… all innovated by civilians… Wildcat loaders and guys with machines who know what a thousandth of an inch is.  the army marksmanship unit sends a team to civilian 3 gun match’s to compete against the best.   They also host an awesome match at fort Benning.  Ronnie Barrett, a dude from Tennessee, figured out how to fit .50 cal in a sniper rifle. Mike Dillon, a guy who sells blue reloading press, devloped mini guns for the secret service.  Swarovski and Vortex optics developed scopes with 1-6 and 1-8 power for the shooting sports that are now used by elite units.   Larue Tactical in Texas developed all the quick change RTZ mounts for these optics.  3gun, USPSA, IPSC, IDPA…  We are a national asset that nobody really appreciates.  
 

 

I made a comment about civilians?

[Centurian52]

50 minutes ago, ALBY said:

.38 caliber = a bore dimension of .357

its where you measure the round. Old Timey stuff.

.38 caliber = 9mm as well 

Ok, but that's exactly what I'm asking for an explanation of. Simply reiterating the issue doesn't explain the issue. I can tell you with absolute certainty that 0.38 inches does not equal 9 millimeters. It equals 9.652 millimeters. And I'm even more certain that 0.38 inches does not equal 0.357 inches (don't even need to break out a calculator for that one). Though 0.357 inches does come pretty close to 9 millimeters (9.0678 millimeters). If 0.38 and 0.357 are the same, then what is 0.38 a measurement of and what is 0.357 a measurement of? Is 0.357 the bore measured to the inside of the rifling and 0.38 the bore measured to the ouside of the rifling?

[chuckdyke]

1 hour ago, Centurian52 said:

And I'm even more certain that 0.38 inches does not equal 0.357 inches

Sorry an 0.357 Magnum is compatible with a 0.38 Special. It chambers the 0.38 Special. They made the case a little longer so 0.38 Special Revolvers won't chamber the 0.357 Magnum. I owned a Model 19 S&W 0.357 Revolver and Model 14 S&W 0.38 Special Revolver so I speak from personal experience. You can use a caliper, and I think you measure the case with a 0.38 Special Revolver and with a 0.357 Magnum Revolver you measure the actual diameter of the bullet. I casted the bullets and used the same mold for both revolvers and the same sizing die. 

[chuckdyke]

The .38 Super is legal in some countries as it is a civilian round but the 9mm Parabellum being a military round is not. I would think a Thompson in .38 super would have been a superior sub-machine gun but they never made such a version. The1911 was very popular chambered for .38 super. A little trivial. 

[ALBY]

8 hours ago, Centurian52 said:

I made a comment about civilians?

Just in the title

 

no worries mate. Just poking some fun.  Does this diagram help ?

 

[ALBY]

If your point is that freedom units are confusing, then I agree with you.

[ALBY]

Maybe this will help. It’s where you take the measurement on the case. 
 

 

[ALBY]

if u put your calipers directly on the pill, its .355 at the base.  the case adds .1 on both sides of the caliper and will read .357, which is the size of the chamber.

competition eats ammo.  when i was shooting competitively, i was loading my own ammo and would produce upwards of 10K pistol and rifle rounds a year.   i could buy components and load for under .10 per round while factory ammo was 5-10X that amount.  

i think what i wanted you to understand about small arms, and what most do not, is that the innovation pipeline is civilian to military.  it is practical shooting and the crucible of competition that has driven small arms innovation for the last 50 years.   a not well understood benefit of our gun culture.  that 6.8 round you mention is a slightly modifed .270 caliber hunting round.  it was developed in the AMU (army marksmanship unit) to give their shooters an advantage over the 5.56 shooters in competition.