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Anyone know why the Germans used centimetres


nheather
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It has always slightly intrigued me why the Germans used centimetres rather than millimetres to describe the calibre of their guns, mortars etc.

 

So the dreaded ‘88’ that the allies would have referred to as 88mm the Germans knew as 8.8cm.

 

Just interested in whether there was a particular reason why they did that.

 

Mind you the British were just as intriguing referring to the weight of the shell, though not consistently, just seems to be army guns.  Mortars and naval artillery used inches.

 

Cheers,

 

Nigel

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Good question Nigel. Can I add why do we get odd sizes such as the 88 mm and not another 2 mm so it’s a 90 mm which is a rounder number. The Lee Enfield .303 springs to mind too. Why the extra .003?  Must be a reason 

 

Apologies for adding a mini hijack but I guess someone on here will know all the answers to both matters

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7 minutes ago, JohnT said:

Good question Nigel. Can I add why do we get odd sizes such as the 88 mm and not another 2 mm so it’s a 90 mm which is a rounder number. The Lee Enfield .303 springs to mind too. Why the extra .003?  Must be a reason 

 

 

 

I have always imagined that is driven by the weight of the shell and charge and the best ballistics.

 

So when we do (did) maths or science questions at school invariably the equations would invariably result in nice numbers.

 

But when working in real life we put the numbers in and out pops something like 88mm as the optimal calibre.

 

I suspect they played with the numbers to get the best compromise of muzzle velocity, kinetic energy, penetration, shell size, cost and out pops 88mm - science and engineering doesn’t care about round numbers, that is a human hang up.

 

As an aside, I read that Volvo are changing the automatic climate systems in their cars so that the user interface only works in whole degrees.  Research found that drivers like to set it at 18 degC or 19 degC but rarely 18.5 degC.  When I read this I realised I do exactly that - the controls in my car have half degrees but I never use them.

 

Cheers,

 

Nigel

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.

 

I wonder whether this is part of the old/outdated "centimetre - gram - second"  ( cgs ) system of measurement which an old European standard and was still being taught in UK schools and used in UK industry in the late 60's (alongside Imperial measures) for metalwork, and similar.

 

See;

 

https://en.wikipedia.org/wiki/Centimetre–gram–second_system_of_units

 

.

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8 hours ago, Phil Gollin said:

.

 

I wonder whether this is part of the old/outdated "centimetre - gram - second"  ( cgs ) system of measurement which an old European standard and was still being taught in UK schools and used in UK industry in the late 60's (alongside Imperial measures) for metalwork, and similar.

 

See;

 

https://en.wikipedia.org/wiki/Centimetre–gram–second_system_of_units

 

.

Could well be, I like that.

 

Cheers,

 

Nigel

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9 hours ago, Phil Gollin said:

.

 

I wonder whether this is part of the old/outdated "centimetre - gram - second"  ( cgs ) system of measurement which an old European standard and was still being taught in UK schools and used in UK industry in the late 60's (alongside Imperial measures) for metalwork, and similar.

 

See;

 

https://en.wikipedia.org/wiki/Centimetre–gram–second_system_of_units

 

.

On the other hand the Germans did not express bomb weights in grams.  

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To go off on a tangent somewhat...

 

It's not helped when some gun calibres are assigned deliberately incorrect sizes - usually to reinforce the fact that one ammunition type shouldn't be used with another gun despite them being identical barrel sizes. The 17 pounder and the '77.6mm' gun on the Comet springs to mind - as does the American 106mm Recoiless Rifle (which was the actually 105mm but used a different ammunition to the previous 105mm RR).

 

John

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18 hours ago, nheather said:

It has always slightly intrigued me why the Germans used centimetres rather than millimetres to describe the calibre of their guns, mortars etc.

 

So the dreaded ‘88’ that the allies would have referred to as 88mm the Germans knew as 8.8cm.

 

Just interested in whether there was a particular reason why they did that.

 

 

 

Because why not? Neither mm nor cm are 'base' units, so either works as well as the other. German practice was to use mm for anything under 20mm and cm for larger. Like any system, it most likely 'just happened' and then stuck.

 

For information, German troops called the 88 the acht-acht, or eight-eight, most likely because 'achtundachtzig' (eight and eighty) is quite a mouthful!

 

Also, to be nitpicky (and I'm guilty of this too), it should be the 8,8cm, as Germany applied the SI standard as it was written, which specified a comma not a point for numeral separators. But that's being pedantic to the extreme. :)

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On 10/5/2019 at 10:55 AM, Phil Gollin said:

I wonder whether this is part of the old/outdated "centimetre - gram - second"  ( cgs ) system of measurement which an old European standard and was still being taught in UK schools and used in UK industry in the late 60's (alongside Imperial measures) for metalwork, and similar.

When I went to secondary school in 1965, we used the CGS system but by the time I was taking O-levels in 1970 we were on the MKS (or SI) system. That's Metres Kilogram Seconds. and moving from CGS to SI was just a matter of moving the decimal point. I used the SI system during all of my career in engineering (until I ended up at an aerospace subcontractor where some things were made in inches as they were for our cousins across the pond) measuring in millimetres or metres, depending on the size. Never ever used centimetres.

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On 10/5/2019 at 10:23 AM, JohnT said:

Good question Nigel. Can I add why do we get odd sizes such as the 88 mm and not another 2 mm so it’s a 90 mm which is a rounder number. The Lee Enfield .303 springs to mind too. Why the extra .003?  Must be a reason 

 

Apologies for adding a mini hijack but I guess someone on here will know all the answers to both matters

 

88 mm was a standard caliber for German naval guns since the pre-Dreadnought era, and the first iteration of the design that later became the well known WW2 88mm gun was initially an adaptation of a medium caliber naval gun, hence 88 mm.

As for the .303, the best possible explanation I've heard is that this is the result of using 5/16 inner diameter dies to make bullets. As the bore diameter for the .303 British is measured on the lands of the rifling, taking the typical height of these off the buller diameter results in a .303 bore.

In any case most official designations of small arms calibres are only nominal, so to know the actual size of bullets and bore diameter it's better to check the relevant published dimensions. There's also the added complication that some bore diameters are measured on the lands of the rifling and some in the grooves...

An example of how things can be misleading: the various US .38 cal. revolver rounds don't have a calibre of .38" ! The bullet diameter is .357", the bore diameter measured on the lands is usually .348-350".  The name .38 however is routed in the history of the oldest of these rounds and has stuck til today. The later .357 Magnum used bullets of exactly the same diameter but got a new name that properly accounts for the bullet diameter, following the US habit of giving a calibre as measured across the grooves ! Had this been a European calibre, would have likely been measured across the lands and called a 9 mm...

Edited by Giorgio N
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  • 2 weeks later...
On 10/8/2019 at 10:05 AM, Giorgio N said:

There's also the added complication that some bore diameters are measured on the lands of the rifling and some in the grooves...

As far as I know, Russia was alone in measuring across the grooves during WW2.  I'm not sure if they still do - not that it has mattered since the 115mm smoothbore on the T-62.  So their 76.2mm guns were 75mm by UK/US standards or 7.5cm by German standards.  Which is how the 76.2mm F22 gun was able to be rechambered for PaK40 ammunition as the FK296(r).  Superior German AP and HE projectiles from German 7.5cm KwK37 ammunition captured in N Africa were able to be adapted to fit US 75mm cartridges in place of the inferior US projectiles and returned to their former owners via the M2 75mm guns on Grants.

 

I wonder if the German measurement designation split had anything to do with the fact that weapons up to and including 15mm are considered to be small arms. They had no weapons in the 15.1 - 19.9mm range so it is a difficult hypothesis to prove.  In the smaller calibres, using mm is easier on the tongue in any language than 0.nnn cm.  In imperial calibres we dropped the "0." part.

 

Obfuscation of actual calibres is nothing new and is surprisingly commonplace, as noted above.  Often to prevent the use of incorrect incompatible but sometimes similar ammunition.  While a .357 Magnum weapon can happily fire less powerful .38 Special cartridges, the reverse is most certainly not true: the .357 Magnum is twice as powerful as the .38 Special, although their bullets are indeed both .357" (9.07mm) calibre and the cartridges are visually similar.  Revolver calibres can be confusing because the calibre stated is often that of the case and chambers rather than the bullet and barrel, which will always be smaller as the bullet fits inside the case.  And revolver cartridges are generally virtually parallel-sided, not necked.  In the past, some calibres like the Long and Short Colts used "heeled" bullets which were stepped to match the case diameter but that practice died out with the advent of smokeless powders.  Thinking German, their "7.92mm Mauser" was actually 8x57mm - which was not the same as commercial 8mm Mauser!

 

A correction on the Comet gun mentioned above.  While called the "77mm HV" it was actually 76.2mm, or 3 inch, calibre.  Same as the 17pdr, and it fired exactly the same projectiles but from a shorter barrel and mated to the shorter and less powerful cartridge from the 3" 20cwt AA gun.  It was a unique weapon incompatible with any other and had to be obviously identified as such.  The Israelis pulled the same trick with the D1504 105mm gun for the M51 Sherman, with barrel and cartridge cut down from the original French CN-105 (although they never used the latter). 

 

Oddly, British AA guns and field howitzers from WW1 on were designated by calibre, in contrast to field artillery and tank guns designated by shell weight.  New artillery weapons changed to calibre designations during WW2 but tank guns not until the 1950s.

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