Cartridge case metric descriptions, 20+mm


Alex - don’t forget that Liberia and Myanmar also use inches. It’s a little unreasonable to demand they switch seeing as only 190 countries in the world use metric.

That’s about metric/SI users vs 383.802.000 inch/imperial/lengths of an andalusian ass measured in chains divided upon one fourtyeights of the weight of a four gallon drum of water users, officially.

But yes - you’re right that not only Norway used metric designations for designs originally planned in inches, just using it as an example.



Well explained Ole!

I mean I do not demand anybody to switch but I refuse to bend over backwards to serve overcome systems.

But the detail I really like here is the fact that you just told me that Liberia and Myanmar are living on the inch side of the world (wasn’t that the flat one?).
Having said this I better run now! :)


not exactly EOD, I’m trying to say original designation first followed by the metric conversion but obviously there would be no need for imperial conversion for rounds that were originally designated in metric.
PetedeCoux explains a whole lot better the point I’m trying to get across.



Let me clarify a couple of things, while pointing out that the designation issue is not just metric vs inch, it’s also metric vs pounders (for both US and UK products of a certain age…).

In my work, guns and their ammunition are described in four places:

  1. Text: Guns grouped by nationality, and within that by approximate date of introduction (or development if experimental). The guns are given whatever their official designations might be (in metric, inches or pounder format) followed by the metric form of the ammunition they used.

  2. Text: Ammunition grouped by calibres, and within each calibre group listed by calibre followed by case length. The ammunition is given whatever its designation might be first (in metric, or inch/pounder followed by the metric equivalent). I’m still juggling with whether or not to separate service from experimental, current from obsolete, or chuck 'em all in together (comments welcomed).

  3. Data table of guns: Listed by calibre followed by case length, with whatever the gun designation might be in the first column and the metric calibre in the second.

  4. Data table of ammunition: Listed by calibre followed by case length, with the metric equivalent calibre coming first. Any other name comes in the final column.

So in only one of the four places is the metric calibre listed first, and that is a table for direct comparison between the dimensions (and performance) of the ammunition.


Tony, as for the experimental vs adopted and service vs obsolete:

It may be difficult to tell when some experimental gun reached a stage when it might have been adopted as all adopted guns were experimental somewhen. And what about not experimental guns which were developed but not adopted by anyone? Do these qualify as experimental then?

And service vs obsolete may also be difficult as who can tell exactly when a gun became obsolete in which place and if it is not in use in some remote place in this world. Many examples of “obsolete” guns in service are known and sure have been discussed here over the years.

So again my only personal view is to have them all in one table/arrangement as telling them apart might be tricky and will bear lots of potential for getting things wrongly attributed or simply allow for criticizm (qualified or not). Just have a column or remark like “adopted” and “not adopted”. The part of service vs obsolete will be way more delicate and I wonder if a statement on this is will really help.


That sounds reasonable - I’ll rejig that chapter!

In the data tables I put those guns which were not adopted for service in italics, and those which are currently in use (as far as I can determine) in bold font.


Tony does good work and his books are very valuable references.
I am confident that whatever form he chooses will be very useful to most readers and researchers in the context of his books.
He is not trying to force everyone connected to ammunition to always use the terminology he chooses to include in the context of his books. In a comparative table listing the added details would be useful to a lot of people.

This is Tony’s issue to decide. Just tell us when the new book is ready so we can buy it!


In an ideal world, we could force them to use metric, for the sake of easiness! Pretty sad to see that pride is more valued than an easy to learn, teach and use system.

Waiting for someone to ask who put man on the moon. But then again - who crashed an orbiter into Mars because they insisted on using Imperial measurements? :-)



2.72155kg 508.023kg ???..I think I’ll stick to 6pr 10cwt myself
Yes they did crash an orbiter but don’t forget they did managed to rescue Matt Damon from Mars too ;-)


That’s an incredibly flawed “logic”.
I see this “argument” a lot on the internet, especially from American DIY- and workshop video youtubers, who dismiss Metric as useless since “1/32 of an inch is sooo much easier than 0.79375 millimeters!”

Well, guess what, we’d probably just use 0,8 millimeters instead… :-)

Same goes for the argument that “it’s much easier to think in feet and inches and Fahrenheit”. When you grow up learning to use Metric it is ten (or hundred, or thousand, or ten thousand… easy system with power of 10s) times easier to use and understand.

I have no difficulty visualising how long 70 cm is or how much water 20 liters is, simply because that’s how I think. And it makes more sense than 2 feet 3 9⁄16 inches.

Whoever can tell me how 1 gallon = 231 cubic inches makes more sense than 1 dm^3 = 1 liter wins a cartridge of their choice from my collection.

Please forgive my semi-off-topic rambling here.


You are making the mistake in assuming every single whole unit will equal a number of small whole units and that these follow a logical sequence (as the metric system does), which isn’t always the case. A liquid U.S. gallon equals 4 U.S. liquid quarts, which equals 8 U.S. liquid pints.

There is also an Imperial gallon, which (not surprisingly) equals 4 Imperial quarts or 8 Imperial pints and of course, lets not forget the U.S. dry gallon, which equates to 1/8 of a U.S. bushel.

I grew up with the metric system and enjoy the simplicity that you describe but I often work in inches when I am machining parts. For some reason .001" is easier to work with than microns. Having said that, I am a metric man through and through, and now wonder exactly what I have won from your collection :)

Whilst metric time didn’t take off, I thoroughly applaud the French for trying to do it simply to piss off the Catholic church, as it would have made it near impossible to have religious celebrations fall on exactly the same day each year!


Myself, I can’t believe that, at age 64, we still aren’t using the metric system! Oh, well, I knew that Liberia was with us, but I didn’t know Myanmar was, too! I feel vindicated! (Riiiiiight!)

One reason that I suggested, above, using a shoulder angle would help with some of those cases that have the same metric dimensions. Otherwise, a comprehensive book would require the use of photos for every different case.

Being rather new to this >20mm group, I have exactly zero idea what any “Pounder” cartridge looks like nor what it measures. While the above comments about measurements not being exact are true, actual dimensions would give me a good idea of where to start looking when I’m trying to figure out what something is.

I want you all to know, however, that I am grateful for any information, no matter where it comes from or what form it’s in!


Well, you could start by reading this: which has information about the relationship between pounder and metric measurements. There’s more information in my data tables:
and you’ll find illustrations of many of the cartridges discussed in my photo gallery:


Metric, Imperial, what’s the problem.? It’s all a mindset. I grew up with imperial and we were forced into metric currency and measurements. To be honest I wouldn’t want to go back to imperial weights, measures, pounds shillings and pence, even though I can automatically calculate the basic measurements in either system.
Ever tried to calculate pounds, shillings and pence on a calculator?
In my mind, decimal is sure the best way. Just my humble opinion