Tell Techno.

[Techno II]

Ermmmm....

What on Earth does it mean when a 'cannon' barrel has a length of 31.4 cal.

How long does that equate to in either feet & inches, or centimeters ?

Asking for a friend.

Cheers - Phil.

[Westmarcher]

cal = calibre.

So, if the calibre is 3 inches, then the barrel length in your example is 94.2 inches. If it's 105mm, it's 31.4 x 105mm.  

p.s. The length of the barrel is usually measured from muzzle to breech. I'm not sure what the measurement parameters are for muzzle loading cannon (i.e., is it the length of the external tube or simply measured from the muzzle to the internal end of the tube?).

[Lord Kermit of Birkenhead]

I'd presume its measured on the internal length. I suspect there was no internetional standard though. You do often see guns described described as 75mm L30 or 40 (Lee and Sherman), 75mm L43/48 (Pnz IV F-J), etc. More lenght = more velocity but above L60 the barrel tends to whip, which degrades accuracy. So the Geman 75mmL70 and 88mmL71 are less accurate than they should be. Modern guns tend to be around L60 for high velocity weapons, howitesrs and other artillery peices are much less.

[Orcs]

We have now sent Techno to sleep

[Ithoriel]

I do wonder if Phil is sometimes left feeling he knew more before our answers!

[Lord Kermit of Birkenhead]

I do wonder if Phil is sometimes left feeling he knew more before our answers!

Well he DID ask....

[Ithoriel]

Well he DID ask....

Child: Mummy where do I come from?

Mother: < long detailed explantion of human biology and reproduction>

Child: No Mummy, Hassan in my class comes from Syria. Where do I come from?

[Techno II]

cal = calibre.
So, if the calibre is 3 inches, then the barrel length in your example is 94.2 inches. If it's 105mm, it's 31.4 x 105mm.  

Thanks Davy.....Though it did take a while to stop the headache. .

In the 'thing' I'm remaking.....The shell would have been 3 inches.....so I'd assumed that that would have been classed as the calibre.....That's what threw me.

(A Browning 50 cal machine gun is called 50 cal, because the bullet is 0.50 inches...isn't it ?..so how does that work, if the barrel is 45 inches in length ?....doesn't that make it a 22.5 calibre ?
No...don't tell me, I'll get another headache....I was virtually mainlining painkillers, yesterday. )

I managed to find an old, perfectly side on, photo of the shooty thing, with a number of troops standing directly behind it....I thought I was going to have to guess their height, and work it from there.

Cheers - Phil

[OldenBUA]

Calibre is the size of a gun barrel, so the cross section, as explained before. So .50 cal is indeed a half inch bullet size. For barrel length, if calibre is used it means simple multiplication, so cal should be read as calibres. A 40mm gun of 60 calibres (often written as L60), would be 40 x 60 = 2400mm = 2.4 m in length.

So same abbreviation (cal), but can mean two different things.

Note, a .50 cal HMG with 45" barrel length would ofcourse be L90.

[Lord Kermit of Birkenhead]

No...don't tell me, I'll get another headache....I was virtually mainlining painkillers, yesterday. )

Gota give you a headachce - no it would be 0.5"L22.5

[Raider4]

The British 15" naval gun barrel is 52 feet long, but is still only 42 calibres.

[Westmarcher]

Gota give you a headachce - no it would be 0.5"L22.5

No, Ian. L90. There are 90 half-inches in a 45 inch length.

[and to confuse everyone further, the Challenger 2 MBT is currently fitted with the L30A1 rifled tank gun but the "L30" has nothing to do with the length which is in fact, 55 calibres long (L55)!]

[Lord Kermit of Birkenhead]

I only teach maths occasionally. The L30 is the model of the 120, we use L like the Yanks use M, ish

[steve_holmes_11]

Now we know what (nn)L(nn) means, can somebody explain why it is used.

We usually adopt classifications that convey something important, or failing that a technical issue.
So who 15"L40 as opposed to 15"L50'.

Is there some "golden ratio" between gun calibre and length (Clearly would vary with role and construction).

[Westmarcher]

Now we know what (nn)L(nn) means, can somebody explain why it is used.

We usually adopt classifications that convey something important, or failing that a technical issue.
So who 15"L40 as opposed to 15"L50'.

Is there some "golden ratio" between gun calibre and length (Clearly would vary with role and construction).

I assume it is simply to inform how long the barrel is. As Ian stated, we Brits use 'L" as part of our weapon model designation and has nothing to do with barrel length. As Ian also stated, longer barrel usually confers increased velocity and so longer range. No doubt there is some "golden ratio" for every type of gun which would depend on the role you want to use it for (e.g., short barrels for howitzers or combat in confined spaces, long barrels for long range shooting and/or greater armour penetration)

Here's a link to the Rheinmetall 120mm tank gun which was originally produced as an L44 and later upgraded by lengthening it to L55 which may help provide further info (or not).   

https://en.wikipedia.org/wiki/Rheinmetall_Rh-120

[Lord Kermit of Birkenhead]

The golden ratio seems to be L55-60 which most modern high velocity guns use. For artillery it can make sense to use shorter lengths to allow for lower minimum ranges to fire close in, but the trend seems to be for longer guns there. As for too long, in WWII our longest A/T gun was the 17pdr at L60, and like I said before the German 75/L70 and 88mm/L71 seem to lose accuracy due to barrel whip as they weren't sufficently rigid to take the firing stresses.

[Techno II]

I've totally switched off, now.

Cheers - Phil.

[Raider4]

I've totally switched off, now.

You can hardly complain when the friendly, helpful bunch that inhabit this place all rush to answer your question.

[Orcs]

You can hardly complain when the friendly, helpful bunch that inhabit this place all rush to answer your question.

I Know. I don't know whys he asks !.  He knows he will get 25 different answers:-
2 will actually be on the subject, but not answer the question
5 will be almost about the same subject but will raise other issues
The other 18 will cover subjects varying from the length of a Mittani skirt, the composition of the bronze in a 16th Century Ottoman cannon. and If Nik Harwood has replied "The hottest Redhead Totty on the planet".

[Scorpio_Rocks]

p.s. The length of the barrel is usually measured from muzzle to breech. I'm not sure what the measurement parameters are for muzzle loading cannon (i.e., is it the length of the external tube or simply measured from the muzzle to the internal end of the tube?).

The "length" of the gun (the measurement given in calibres) is actually the length of the bore - so internally muzzle to inside of breach, doesnt include all breach, muzzle brake, etc.