Everyone knows how powerful and fearsome the "88" was; why didn't the designers just round up to a 90mm? Still would have been powerful; just wondering

'H' is the 8th letter of the latin alphabet. 'Heil Hitler' corresponds to '88'...

Joke aside, it has probably something to do with the fact that 88mm was originally designed as an anti-aircraft weapon. Typical anti-aircraft artillery tends to be large and heavy. Knowing German accuracy, the caliber was probably carefully chosen in order to deliver maximum punch at minimal weight. Just my two cents...

The 88mm Flak gun was devoleped from an existing German 88mm naval gun. It was wildly effective and well-liked by the troops. It was a case of "if it aint broke, don't fix it". Bottom line, there was no reason to spend lots of money and time to develop a new 90mm gun. Two mm doesn't really make that much difference and would have cost a bunch of money and time to develop.

You could ask that about any calibre that didn’t end in a round number (US 76mm, Soviet 76.2mm. German 3.7cm, British 3.7”, Japanese 47mm etc.). Ultimately the bigger the calibre, the bigger and heavier the projectile, the more propellant it needs, the bigger the gun to withstand the recoil forces and the bigger and more powerful the towing vehicle. There are no free lunches in ordnance design (and many other fields) so the idea is to design to meet a requirement rather than just to have calibre as some nominal value for spurious ‘tidiness’.

That makes lot of sense.

It was always my understanding that the majority of the periods gun bore sizes were based on British Ordnance Standards. For whatever reason most forces 'copied' these sizes, i.e. 37mm was the bore size of a 1 pound round; 76mm was the bore size for 12 through to 17 pound; and 87.6mm was the bore size for 25 pound rounds.

Thanks guys; hadn't really researched it; the question just popped into my head during one of those times of early AM wakefulness; all the stuff everyone is saying makes sense; thanks again;

Something else to take into consideration are resources. Germany did not have a vast supply, such as Russia or the United States. If the 88 was effective, why use more resources for a larger round?

Instead of developing the too-heavy 128 mm PAK, they should have adapted the FLAK 38/39 105mm. Very similar to the 88 but with harder punch, and it was already in production. It also became a standard NATO caliber post-war, so it must have been effective.

Something to ponder. US upgrades-75mm, 90mm, 105mm, 120mm
USSR 85mm, 100mm, 115mm, 125mm. Except for the last Russian up grade there is a 15mm change. Probably not a coincidence.

Interesting pattern. Thanks.

First, I haven't read through all the posts so please forgive redundancy.

As Ian Barraclough wrote, the categorizing guns and howitzers by bore diameter was probably a reclassification from the weight of the projectile. The 57mm ATG was a 6-pounder. I haven't looked but perhaps the 47mm was 5 pounds? Or perhaps some countries adopted the weight of the shot/shell to metric, or simply designed for the gun size without concern for shot weight? That could account for seemingly odd sizes like the Soviet 45mm, Wehrmacht's 50mm and 75mm, the Madsen 27mm, and the eventual Soviet 23mm, the US 114mm/4.5in gun, etc.

The we get up to some naval weapons (classes like the British 3.7in): 5in; 5.5in; 6.1, etc.

I don't know most of the answers but I think it is a very interesting thread. Kinda like why did some model companies create some scales that don't seem to scale to Empirical nor metric, i.e., 1/35, 1/700?

I look forward to more posts.

If the original 88 was developed from a naval gun, these weapons originally expressed their calibre in inches. 88mm is very close to 3.5".

Lots of strange metric sizes can be explained by checking the corresponding inch measurement (fractions or decimals).
Rifle calibre 7.62 mm (why not 7.5?) = 0.3 inches
Haven't figured out the background to the .303 caliber though, 7.7 mm is also an odd size.
.22 comes out as 5.59 mm
75 mm could a rounded off value for 76,2 which is 3 inches
likewise for the 155 mm guns, very close to 6.1 inches
the Soviet/Russian 152 mm is the 6 inch guns,
203 mm (why not an even 200??) is 8 inches
et.c.
Some measurements have been tweaked slightly to fit measuring tools made for the metric system

3.5 inches comes out to 88.9 mm, why not round it up to an even 89 mm? or 90 mm
maybe 88 was easier to remember, looked better, was easier to pronounce or whatever ....

I'm pretty sure .22 was a weight based bore, that is, a sphere of lead of .22 inch diameter weighed some round or integer increment of a customary weight unit. The British .303 may be the same.

There is also the matter of designation. The US 76mm and 3-inch guns were the same caliber and even used the same projectiles; the designations were different to avoid confusion in supply. Likewise, the 106mm recoilless rifle got its size to distinguish it from the earlier but functionally incompatible 105mm RR.

KL

Interesting thread. One of the issues with SAA is that many of the calibres are nominal depending on whether you measure the bullet or the cartridge. There are also deliberate anomalies such as WW2 British 9mm ammo being slightly larger than German, allowing the use of German ammunition in a Sten, but not vice-versa. Can't explain the Italians choice of 6.5mm (quarter of an inch is 6.35mm, which works nicely with Russian 12.7mm, half inch or .50 calibre), although the Arisaka now makes sense at 7.7mm - it's an Imperial measurement! The Japanese, with no engineering tradition adopted British and American technology and copied it. Interestingly (and off topic) drive chains fitted to Japanese motorcycles are still in Imperial measurements, not Metric.

Many cannon bore sizes actually go back to projectile weight which is guns were graded going back to Gustavus Adolphus and before. I remember seeing that one type of 24 pounder cannon had a 88mm bore.