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Understanding Gun Designations

Winterhawk
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Winterhawk Member

Winterhawk

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A Panzer IVF has a 75/L24 gun and a IVF2 has a 75/L43 gun. Numerous tanks and field guns make use of a similar numbering convention. I'm aware that the first number references the diameter of the barrel (bore) of the gun in mm.

Is the second number a measure of the length of the barrel? If so, how you determine the actual length from, let's say, L43? Neither 43 or 430 (mm's, cm's or m's) make sense. Neither does 4.3 m's.

Perhaps it's not a reference to the length?

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Thomas Goetz Member

Thomas Goetz

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I'm going by memory here, so I hope this is accurate. The second number does indeed refer to the length of the barrel, but not in any standard units of measurement. The number instead refers to (I believe) multiples of the barrel diameter (The first number) So a 75mm/L24 has a barrel 75 mm in diameter at the muzzle, and 24 times that distance (1800 mm, or 1.8 meters) in length. A 75/43 has a barrel length of about 3.23 meters.

If I'm wrong, I'm sure someone else will correct me, but I'm fairly confident of this, at least for the German guns. Hope this helps.

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gunnersman Senior Member

gunnersman

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Posted
Originally posted by Winterhawk:

A Panzer IVF has a 75/L24 gun and a IVF2 has a 75/L43 gun. Numerous tanks and field guns make use of a similar numbering convention. I'm aware that the first number references the diameter of the barrel (bore) of the gun in mm.

Is the second number a measure of the length of the barrel? If so, how you determine the actual length from, let's say, L43? Neither 43 or 430 (mm's, cm's or m's) make sense. Neither does 4.3 m's.

Perhaps it's not a reference to the length?

Oh, oh, oh I know this one!

The second number is the number of rounds it would take to equal the length of the barrell, measured by their width. Or, the diameter of the bore. Take your pic.

[ October 07, 2002, 03:00 PM: Message edited by: gunnersman ]

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Barticus Senior Member

Barticus

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If I recall correctly, you multipyly the 'L' number by the calibre to get barrel length.

ex. 75L24 = 75mm bore, 1800mm barrel length

75L43 = 75mm bore, 3225mm barrel length

Now if someone would kindly explain exactly how barrel length is measured, i.e. length of rifling, bottom of firing chamber, overall length, I would appreciate that too.

B

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Thomas Goetz Member

Thomas Goetz

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Silvio:

Don't know if anyone besides the Germans used this system for designating their guns. So Russian equipment may well not have such indicators. As for the towed stuff, I'm fairly sure it's in there somewhere. And as for the big cats, well, the Tiger I has an 88mm/L56 gun, and the Panther a 75mm/L70. I think (not sure) that the King Tiger has an 88/L70, which is the same gun used on the Jagdpanther. Most Stugs used either the 75/L43 or 75/L48, but the Jagdpanzer IV (later versions) used the Panther's 75/L70. Not sure what the L number of the Hunting Tiger was, but I'm sure it had one.

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Jeff Heidman Senior Member

Jeff Heidman

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Originally posted by blazethedog:

Dang Tom, you are not only smart, but right too(I think) I work with the Dod folks and someone explained it too me very close to what you said. Now, tell me were caliber falls in here for the US folks?

One caliber, IIRC, is an inch. So a .50 caliber gun is the same as a half inch, or about 12.7mm.

The US 3" gun, for instance, is 3*12.7*2 = 76.2mm.

The Brits, of course, had to be different, and rate their guns by shell weight, a rather bad idea since shell weight varies so much.

I think the standard has become to use the XLY notation.

Jeff Heidman

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John D Salt Senior Member

John D Salt

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Originally posted by Barticus:

If I recall correctly, you multipyly the 'L' number by the calibre to get barrel length.

ex. 75L24 = 75mm bore, 1800mm barrel length

75L43 = 75mm bore, 3225mm barrel length

Now if someone would kindly explain exactly how barrel length is measured, i.e. length of rifling, bottom of firing chamber, overall length, I would appreciate that too.

I gather from some of the notes in Hunnicutt's "Sherman" that the American (and I think British) convention was to measure the length of bore to the front face of the breech, and German to measure to the back face. As far as I can determine, both of these ignore muzzle brakes. I'm afraid I can't find what the Soviet convention was (nor the French, the Italians, the Japanese, nor anyone else). For the sake of a blind guess I would imagine that the English-speaking nations did it one way and the "continentals", i.e. everyone else, did it the other. If anyone knows better, please shout.

All the best,

John.

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Guest Mike

Guest Mike

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Gak - no, 1 calibre is NOT 1"!! :(

A calibre is the bore of the gun.

So 1 calibre for a 3" gun is 3", for a .50 it's .50", for a 170mm it is 170mm. a 100 calibre .50" wo0uld be 50" long, a 100 calibre 3" would be 300" long, and a 100 calibre 170mm would be 17000mm long, which is why the 170 was only a 30 calibre of something like that!! smile.gif

It is a useful measure because the volume of gas required to fill the bore and hence propell the shell is a 3-D value, and measuring gun length in calibres gives a 3D value with a single measure that can be compared across guns of different sizes.

Eg an L24 gun is a short barrel, an L70 is a long barrel for whatever size gun you'er talking about.

Barrel length (in calibres) relates to achievable muzzle velocity, and hence armour penetration.

Short guns use less propellant and hence get less velocity. Long guns can use more propellant and hence get more velocity.

Rmember that propellant accelerates teh shell by turning into gas through combustion, hence creating pressure behind the shell and forcing it along the barrel. The trick is to have just enough propellant in the charge to accelerate the shell for the length of the barrel, and no more or less.

Loading up a short gun with lots of porpellant doesn't do much because once the shell is out of the muzzle the excess propellant no longer accelerates it - it just produces an almighty muzzle flash!!

Long guns with small propelling charges can lose muzzle velocity if the pressure behind the shell falls geenrates less force to less than the drag of the shell along the barrel - the shell could conceivably sklow down while still in the barrel!

Long guns will often have smaller charges for HE than AP rounds - and hence lower muzzle velocities for hE - this also lowers wear on the barrel and extends its life.

[ October 07, 2002, 04:26 PM: Message edited by: Mike ]

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Silvio Manuel Senior Member

Silvio Manuel

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Originally posted by Thomas Goetz:

Silvio:

Don't know if anyone besides the Germans used this system for designating their guns. So Russian equipment may well not have such indicators. As for the towed stuff, I'm fairly sure it's in there somewhere. And as for the big cats, well, the Tiger I has an 88mm/L56 gun, and the Panther a 75mm/L70. I think (not sure) that the King Tiger has an 88/L70, which is the same gun used on the Jagdpanther. Most Stugs used either the 75/L43 or 75/L48, but the Jagdpanzer IV (later versions) used the Panther's 75/L70. Not sure what the L number of the Hunting Tiger was, but I'm sure it had one.

In CMBB the Soviet caliber #'s are actually listed for most, but not ALL guns...like I said one of the Soviet towed 76mm's doesn't have one. Maybe it's the 85mm AA gun...it just says 85mm instead of 85/L55 or whatever.

One of the German 75mm inf.guns doesn't have it either, but looking at it, one can see that it *doesn't have a barrel*...it looks like a sawed off shotgun cannon...maybe it's the 'mountain gun?'

Some tanks only say (example) 85mm but not L...

The German mid-length 75mm is quite nice...anywhere from L43 to L51 or so for Marder II or III. The Sherman is only a 75mm L38.

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StellarRat Senior Member

StellarRat

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Originally posted by Mike:

Loading up a short gun with lots of porpellant doesn't do much because once the shell is out of the muzzle the excess propellant no longer accelerates it - it just produces an almighty muzzle flash!!

You can control some of these factors with shell weight, the burning speed of the propellant, and strength of the barrel too. But I agree with your general statement, longer barrel more velocity, shorter barrel less velocity.
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Pfc Driscole James E Member

Pfc Driscole James E

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Originally posted by Thomas Goetz:

Silvio:

Don't know if anyone besides the Germans used this system for designating their guns. <snip>

I was an Electronics Tech not a Gunner's Mate.

The United States Naval Service uses the same sort of system on guns. My last ship the Glamorus and Exciting USS Holder, DD-819 Home of the Boy Commandos, had 5 inch 38 twin mounts. Were 5 inch is the caliber of the gun, I.E. the internal diameter measured from land to land, and the rifleing was 38 calibers long, 190 inches or 15 feet 10 inches. In metric that should be 127/38.

More modern ships have 5 inch 54s but use the same projectiles and powder cases, with ajustemnets made to the cams for analog or the parameters for digital balsitic computers.

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ianc Senior Member

ianc

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Loading up a short gun with lots of porpellant doesn't do much because once the shell is out of the muzzle the excess propellant no longer accelerates it - it just produces an almighty muzzle flash!!
Yes, but with more propellant, wouldn't you get a greater force behind the projectile, thus causing a greater acceleration as it travelled up the barrel?

ianc

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StellarRat Senior Member

StellarRat

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Originally posted by ianc:

Yes, but with more propellant, wouldn't you get a greater force behind the projectile, thus causing a greater acceleration as it travelled up the barrel?

ianc

To certain point that is true, however, since the acceleration is a squared function the amount of stress on the walls and rifling of the barrel goes up much faster than the corresponding increase in shell velocity. Eventually, the rifling or barrel is damaged. It is much more practical to add length to the barrel and give the expanding gas more time to accelerate the shell. As a side note: A lot of modern guns are smoothbore. This allows a more velocity because there is no drag on the shell from the rifling and you don't have worry about ripping the rifling out of the barrel by forcing a shell down it too fast.

[ October 07, 2002, 07:26 PM: Message edited by: StellarRat ]

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Guest Mike

Guest Mike

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Originally posted by ianc:

Yes, but with more propellant, wouldn't you get a greater force behind the projectile, thus causing a greater acceleration as it travelled up the barrel?

This is just a fraction beyond me for a sure answer, but my edumicated guess would be no.

IIRC propellant burns - it doesn't explode instantaneously, so the expansion of the gas takes place at a fixed velocity regardless of the quantity. If it were otherwise then there'd be a lot less need for long barrels to generate AP performance - you could just fit new breaches to take larger charges.

You do get more force by taking a faster burning propellant tho, and changing propellant has been known to occur - particularly in naval weapons that I'm aware of.

[ October 07, 2002, 09:26 PM: Message edited by: Mike ]

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