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The Great War (1914-1918) Forum

Remembered Today:

artillery bore size


David B

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Hi,

One thing that has puzzled me for a long time is what is the criteria for picking a size of bore for artillery weapons.

i.e 9.2 inch - it seems an odd size, surely 9 inch or 10 inch would have been easier to manufacture, or is that

size needed to produce a weight of ammunition that was required. Other sizes come to mind 4.7 inch in both army and

naval gunnery, at least in the navy's case this was reduced to 4.5 - makes it much easier to use the ruler.

David/Canberra

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I don't see how 'logical' or neatly rounded calibres should make any difference at all. Nobody actually uses a rule to either measure the shells in production or the bore in service. We're talking reasonably precision engineering here with the instruments to do the job. Generally calibre is based on the need for particular performance.

That said, odd imperial measurements may be rounded in metric (4.7?) and suggest the UK manufactuer may have derived a gun from something produced for foreigners. Others may have their origin in a requirement for a projectile of a particular weight, which again refelcts performance requirements.

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David

I suspect that when you question the odd sizes quoted for British artillery weapons you are assuming that these weapons were developed in Britain. I think you'll find that in many cases the weapons used in Britain were modifications or developments of european weapons.

The 4.7 inch that you quote is the imperial measurement equivalent of the continental 120mm. If you take any British measurement and multiply it by 25.4mm you will end up with a continental equivalent with which you are probably familiar.

Despite nigelfe's assertion that nobody measured the bore or calibre the opposite is the case. Artillerymen developed callipers that measured bore and calibre. This process became part of the function of the manufacturers and nowadays would be called quality control. Otherwise 'precision engineering' becomes 'imprecise engineering'.

Garth

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Hello all

I once put this question to a professional artilleyman (he had been project manager for the current British 155mm howitzer) and he confirmed that performance, principally the projectile weight was the main factor, although he also said "but I'm not a ballistician."

The only British calibre I know of which was definitely based on a metric original is 9.45 inches, which comes from 24cm weapons developed in Germany. In any case a gun nominally of 15cm calibre may actually have a calibre of 15.2 or 15.5cm.

Naval and military guns used the same calibres because they were basically the same weapons using different mountings. Most of the railway guns used in France were taken from stocks of reserve barrels made for battleships.

I also wonder why the rifle calibre is 0.303. I believe the modern equivalent is 7.92mm., which rather destroys the concept of "exact" metric equivalents!

Ron

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Hi all,

thanks for all those replies - really I am not knocking the fact that these odd sizes were developed in UK

or "having a go" but merely to try and ascertain whether these sizes were developed so as to be able fire shells of

a predetermined weight. In my case when I was in the navy most destroyer guns were of 4.7 inch (with 4 inch for AA)

These eventually gave way to 4.5 inch, presumably a newer and better gun that was fully enclosed and had a higher

firing rate. Mind you I was not a gunner but a communicator.

David

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Despite nigelfe's assertion that nobody measured the bore or calibre the opposite is the case.

I don't normally quibble with being misquoted, but what I actually said was that no one used rulers for measuring these things, they used instruments. The point being that instruments were designed to measure thousandths of a inch or whatever, and machine tools in ammo factories set up accordingly therefore measurements convenient for rulers was not an issue.

As for measuring bore diameter, this is routine in-service equipment management. Modern practice is that a barrel should be replaced when its calibre has increased by about 3%, in WW1 barrels got far more worn. I think in WW1 records of bore measurements were kept in each gun's Memorandum of Examination, the measurements would have been routinely taken by the bty's artificers. I'm not sure when they stopped using 'calipers' for bore measurement, but is was many decades ago. Although bore measurement was normally one inch forward of the commencement of rifling, sometimes measurements had to be taken at different positions up the barrel which is a tad tricky with normal hand held calipers (or rulers)!

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I once put this question to a professional artilleyman (he had been project manager for the current British 155mm howitzer) and he confirmed that performance, principally the projectile weight was the main factor, although he also said "but I'm not a ballistician."

Of course modern calibres are internationally agreed, 155 originated in France in WW1 and was adopted by US, as was 8-in from UK (and subsequently called 203mm). The UK equivalent of 155 was 6-inch, usually called 152mm metrically. Then we have 3-in normally called 76mm but more precisely 76.2. 75mm has been called 2.95-in in UK service.

Its also worth noting that weights can vary quite widely for a calibre, for example the WW2 5.5-in had 100 lb and 80 lb HE shells. Even modern 155mm designs vary between about 90 and 105 lbs.

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A few years ago on another forum I read that the caliber designations of small arms and their ammunition are more nominal than actual, and that over the years we have accepted those designations because they are the agreed-upon way of identifying them. The point the writer was making was that if one were to go back and use a single internationally-recognized standard for measuring all the cartridges made at various times during the last 150 years we could redesignate the caliber names of about half of them.

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Interesting topic, even for a non-artillery person like me. But it also causes me to wonder what space there would be - typically - between the outer casing of the shell and the inner diameter of the barrel. I know that the driving band was soft metal that 'screwed' its way into the rifling, but if the gap I'm referring to was more than a very tiny gap, surely this would cause the shell to wobble and not have a true trajectory? Especially when the barrel was hot and/or worn and therefore the gap would be larger?

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Hi guys,

I dont think anyone has yet got the point of my original question - Why 9.2 inches - surely 8.78879 inches

would have been just as good query. I personally think it was that 9.2 inch was probably the optimum size for a

specific requirement but dont know for sure. All I can say is that the 9.2 must have been a wonderful gun (howitzer)

it was the only weapon my grandfather ever talked about (he being the RSM of a HAG which mounted 9.2's).

Unfortunately in my youth this info went in one ear and out the other - dont we all

Regards David/Canberra

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I personally think it was that 9.2 inch was probably the optimum size for a

specific requirement but dont know for sure.

Basically yes, David. Its use in the Navy pre-dates that in the Army, and as naval weapons had more constraints of size in their mountings, 9.2-inch was probably a way of getting better performance (range and shell weight) than a 9-inch, and a 10-inch would be too big.

The 9.2-inch howitzer used by the Army was indeed a weapon highly regarded by its users. If you ever get to London, you will see an example in stone, crowning the Royal Artillery memorial in Hyde Park.

Ron

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Hello all

I also wonder why the rifle calibre is 0.303. I believe the modern equivalent is 7.92mm., which rather destroys the concept of "exact" metric equivalents!

Ron

Unfortunately when you start talking about rifle calibres it opens a whole new can of worms! is it bore diameter? Groove diameter? Bullet diameter?

The .303" has it's origins in the 7.5mm round developed by Major Rubin at Thun Arsenal in Switzerland and during the development process there were .305" and .306" cartidges. A new .303" barrel will have a bore diameter of maybe .301" and a groove diameter of .308" firing bullets of .311", so what do you call the calibre?

The modern equivalent is 7.62mm (not 7.92mm) which is the metric equivalent of .30". The Russians were the first to use a calibre of 7.62mm in 1891, but that was because they had a version of the imperial measurement system and they regarded the calibre as three tenths of an inch. Similarly that is why they have an artillery calibre of 76.2mm, i.e. 3 inches.

In the end it often comes down to finding a name for the calibre that distinguishes it from another similar one.

Regards

TonyE

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Hi guys,

thanks for all the informed replies - yes Ron I have seen the memorial in Hyde park - most impressive. Incidentally

we have a real one (9.2") in the AWM in Canberra.

David

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From the Handbook for the B.L. 9.2-inch Marks I & II Howitizers on Marks I & II Cariiages, Land Service, 1931.

Bore:

Calibre - 9.2 inches (calibre is always measured between the lands (the high bits) in artillery barrels)

Length - 121.5 inches and (Mk 2 159.16 inches)

Chamber:

Diameter - 9.8 inches

length to base of projectile - 8.1 inches and (Mk 2 34.035 inches )

Capacity - 660 cu inches and (Mk 2 2600 cu inches)

Rifling:

System - Polygroove P.S.

Lenght - 110 inches and (Mk 2 121.25 inches)

Twist - Uniform 1 turn in 15 calibres and (Mk 2 1 turn in 25 calibres)

Number of grooves - 56

Projectiles, this edition of the HB only lists HE proj Mks 14 to 19 and Common Shell Mk 1. They vary in length from 27.24 inches to 32.1 inches, with the HE bursting charge from 25 lbs 12 oz (common shell) to 43 lbs 11 ozs (MK 17), all weighed 290 lbs in total when fuzed.

Proj Diameter:

Driving band - 9.365 inches

Body - 9.185 inches, for the arithmetically challenged this gave 0.015 inches of windage in a new barrel, probably about the thickness of the paint! As barrrels wore not only did muzzle velocity reduce but wobble increased and the shell became less stable in flight.

0.015 inch windage seems the norm for Howitzers, at least for the later mks of shell. 60-pr data is interesting the Mk 1 shrapnel and other early mks had 0.03 inches, but later mks were 0.01. I hadn't hadn't previously spotted this, I need to do a bit more research but it seems likely that windage was tightened up in the course of WW1, probably connected with increasing ranges and dispersion issues.

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Thanks for your time nigelfe I am continually amazed at the wealth of information that can be

found from members of this forum

David/Canberra

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Hi,

I thought I had left all this behind when I became an Ex-Gunfitter!

I would have thought that for day to day firing checks the use of a Gauge Plug Bore (basically, a large lump of steel machined to a standard size, passed through the bore before and after the day's firing) would have been sufficient for ensuring the bore was still ok to fire. Only on more detailed inspection would the precise measurement need to be known.

These days, slip-over gauges are used to measure the bore. This is, basically, two plates held together by a couple of screws and nuts tight enough for them to stay put, but loose enough for them to move under pressure. They are set to a diameter larger than the bore and then using rods they are pulled through an arc and the bore diameter closes the plates to the precise size.

I'll come back to this later.... A bit pushed for time right now.

I'm back!

The driving band has a couple of functions, the most important of which is to impart rotational spin which aids stability and therefore accuracy and range. Next, it provides forward obturation - a gas tight seal - which allows the correct shot start pressure to build up before the projectile moves through the bore and ensures correct muzzle velocity. Rearward obturation is prvided either by the breech mechanism in separate ammunitions or by the shell cases in fixed and semi-fixed ammunitions. Slack fit between drive band and bore makes for a lower pressure for the shot start point which would cause drop-shorts due to the muzzle velocity being slower than expected and the range being reduced by wasting the potential of the charge used to fire the projectile.

Cheers,

Nigel

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Who ever said that the military mind was logical? 4.7 inches makes as much sence as 88mm!

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