Gun Caliber

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Subject: Gun Caliber
technoid 7/20/2004 9:48:12 AM

Here's another question that probably shows my ignorance in the subject of large guns but I noticed in looking at web sites for large cannons that the term "caliber" is used differently for large guns. In the realm of small arms "caliber" is the bullet or bore size. When talking large guns it appears the term "caliber" refers to barrel length. Why is this different and how did it come about? In small arms the barrel length is simply refered to in units of length like "inches".

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k3n-54n RE:Gun Caliber and ammo weight 8/14/2004 4:24:52 PM

IsoT, a four pounder is bigger than a two pounder. I don't think they were based on lead spheres, but, even if they were, the measurement is basically the inverse of guage. One of the fun things about ammunition is the variety of ways in which it is described. While anyone with any sense must find it appalling and chaotic, I say that is the charm.

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french stratege RE:Gun Caliber and ammo weight 8/14/2004 9:20:38 PM

Calibers is not tube lenght but diameter.It translate from the French term "calibre" which mean the diameter of an hole.If we say 50 time calibers to exprimate the lenght of a gun it is because it shows immediately potential performance as a piston pressure ratio in a explosive engine of a car.

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technoid RE:Gun Caliber and ammo weight 8/18/2004 4:38:38 PM

I think I've finally figured this out and it's not nearly as complicated as I wanted it to be. Based upon the discussion and the reponse from the kind Frenchmen I have drawn a reasonable conclusion how the terminology confusion came about. If the bore diameter is from the French work "calibre" I would conclude that the term caliber as applies to tube length was just a convention developed to express the length as a function of bore size. I would guess that as "french stratege" has implied that folks simply began to shorten the terminology and rather than talk about a barrel being 38 calibers long they simply began calling it a 38 caliber tube. There is probably no more explanation than that. Well, for what's it worth I learned something, thanks for all the discussion.

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neutralizer RE:Gun Caliber and ammo weight 8/26/2004 5:09:57 AM

For artillery calibre is always measured between the surface of the lands in the bore. The shell is different, the dimaeter of the body is slightly less than the calibre and the diameter of the driving band is rather more. Correctly 'calibre length' is one way of definging barrel length in terms of the barrel's calibre. Sloppy users who perhaps don't really know what they're talking about have got into a habit of talking about 'calibre' when they actually means 'calibre length' in relation to the barrel's length. It seems to be a fairly modern practice (well after WW2)in widespread use. The problem is there isn't any agreement on what's being measured and what it means. Barrels have several lengths, about the only thing that seems commonly agreed is that barrel length excludes any muzzle brake. Barrel length could be the length of rifling, the length from breech face to muzzle face, muzzle face to the rear face of the barrel when the breech assembly is removed, or perhaps even to the rear face of the breach assembly. Historically, many European armies gave names to different size cannons (culverin, etc). It's also quite reasonable to give a standard weight for a modern gun's shell it is merely 'the shell weight for which the firing table is compiled'. The Brits only designated 'guns' by weight, 'howitzers' were designated by calibre. However, for real confusion over calibre you have to turn to small arms, eg the UK's latest 'long range rifle', it fires an ammo usually given in inches in the US, MoD give the weapon a metric calibre, try converting the inches to mm or vice versa! I guess this is one for another thread, but I suspect NATO has an agreed method of measuring small arms calibre but ammo manufacturers don't use it.

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fatarian 10/13/2007 7:24:45 AM

In my country , they alway describe the howitzer as 155mm 52 caliber...while i understand ( correct me if my understanding is wrong) that 155mm means the diameter of barrel, by 155mm x 52 caliber = 8060mm barrel length..i still don understand why 52 calibre. How do i undestand the term 155mm 52 calibre..........does 52 calibre means there is 52 rifling in the barrel........if 52 calibre means the diameter of the bore, then what does 155mm means...? Thanks

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neutralizer 10/13/2007 7:47:30 AM

'52 calibres' merely means that the barrel is 52 calibres long, but as I previously pointed out there are differnt ways of measuring the length of a barrel in terms of how you define the end points.

NATO agree to use 155mm calibre in the 1950s. At that time 155mm Howitzer barrels were typically about 24 calibres long. 155mm Gun barrels were rather longer. In 1963 4 NATO nations (GE, IT, UK US) agreed to a standard 39 calibre barrel, this was/is used with M109A1 and later marks, M198 and FH70. In the early 1990s 5 nations (FR joined) agreed the specification for a 52 cal barrel, basically this was a UK design. Some nations have used different lengths in the period, FR (pre 52 calibre) and S Africa being the best known.

Actually barrel length alone doesn't mean very much, it has to be coupled with such things as chamber volume and peak pressure, and for a max range it also needs a max MV and a shell with particular ballistic characterics.

The use of the 'L' prefix for calibre length, eg 'L52', is not an agreed practice and is only used by a few coninental European nations.

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flamingknives 10/13/2007 8:03:43 AM

If someone were to say 52 calibre, it would probably be on the basis that the calibre of the gun is already known.

Typically 52 and 39 calibre lengths are associated with 155mm guns, and 44 and 55 calibre lengths are associated with 120mm tank guns. If you wish to be clear, however, it is best to state the base calibre as well as the calibre length.

However, the Americans like to confuse things by describing small-arms calibres such that a 0.3 inch calibre is a "thirty-caliber" and a 0.5 inch calibre (the famous M2) is a "fifty-caliber"

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Jeff_F_F 10/13/2007 8:23:57 AM

Think of the "L" as an "x" or "*" meaning "multiplied by" They are two dimensions. 155mm (wide) x 52 calibers (long). For a concrete example the original Rhinmetall gun used by Leopard 2 (where it is known as the L11) and upgraded M1 (where it is known as the M256) is 44 calibers long - 120mm L44. An upgraded version has been designed that is 55 calibers long 120mm L55. If we knew nothing else about the guns and ammunition used we would be able to say that the same armor piercing ammunition fired from the L55 gun will have a significantly higher muzzle velocity and hence better penetration than that fired by the L44 gun.

A rule of thumb for WWII era weapons was as follows a gun of any given bore size was generally:

<30 calibers long : howitzer

30-45 calibers long : artillery gun or low performance antitank gun.

45-60 calibers long : good performing antitank gun.

>60 calibers long : high performance antitank gun.

Over time, advancing technology changes things. A modern L44 antitank gun has a similar muzzle velocity as the World War I 210mm L160 Paris Gun.

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fatarian 10/14/2007 10:13:16 AM

Please pardon my ignorance that i still don understand what your mean. Let me re-phase my question

1. 155mm means the width of what component ?

2. 52 calibre means the length of which component ?

3 If calibre means the diameter of the bore , then it should be 155mm calibre ... However, why 155mm 52 calibre....

4. 52 calibre means 52 rifling in the barrel. That is why the artillery gun when fired will always have drift that we need to apply compensation.

Thanks

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flamingknives 10/14/2007 10:34:34 AM

Calibre is the bore of the gun, although there are a number of different ways of measuring it (land diameter, outermost rifling diameter, half the depth of rifling diameter). So that is the 155mm dimension on an M777, for the sake of example.

The length should be in ablsolute units (mm, m, feet, whatever) or in calibre lengths (possibly calibres - noting the 's' on the end). So, for the M777, it has a barrel of 39 calibre lengths, or calibres. For a gun with a 52 calibre length barrel, one could say that the gun was 52 calibres long. Speaking purely in terms of calibre lengths (which might be contracted

to calibres), say comparing a 39 calibre gun to a 52 calibre gun would assume that all parties know which calibre is being discussed. As with much of the English language, it is context sensative.

Rifling, AIUI, is designated in terms of number of grooves and rate of twist. Since rotations will be one, the nature of the other unit (mm, m, feet, calibre length, whatever) is critical to get it right.

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