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Gun length in calibers

Posted: Tue Oct 10, 2006 8:44 pm
by Dave Saxton
We see the use of 16"/L50, 16"/L45, 15"/L42 and so forth.... The Lxx refers to the guns length, but what does it really mean, and are we getting a direct comparison from gun to gun?

On guns with interruped screw breach blocks, using bagged charges, the distance is not the overall length of the gun. It's the distance from the muzzle to the closed breach. Usually on an interrupted screw breach type gun, the breach and screws use up about two calibers in length. For example, The 16"/50 used by the Iowa class is about 52 calibers long overall. 50 calibers is the distance from the muzzle to approximate point were the projectile seats, plus the combustion chamber.

The large German guns used a cartridge main charge, with a small bagged fore-charge, and a sliding breach. Totally different. Therefore the methodology to determine gun length must be different.

For example, Bismarck's 15 inch gun had an overall length of 52 calibers. It's correctly refered to as a 38cm/L52 gun. The distance from muzzle to breach is 48.5 calibers. This distance could be used, but it's still not a good point of comparison, because of the German gun's use of a cartridge charge (that seals itself) and only a very small combustion chamber for the fore-charge.

The distance from muzzle to where the projectile seats is more difficult to pin point, because the German projectiles used multiple driving bands, not all positioned together. The distance from where the projectile seats to the muzzle, or the inner seelen lange, is unusually long on the Bismarck class 15" gun. It's actually longer than this distance in the Italian 15"/50 gun, because the Italian gun uses a large combustion chamber for bagged charges. The distance that the shell travells under pressure of the expanding gasses in the German large naval guns is longer than any other large naval guns, that I know of, except the Iowa class 16"/50 gun. This distance in both is about 43 calibers. ~43 calibers is significantly longer than the usual.

There is no internal or external distance of 47 calibers for the Bismarck class 15" anywhere to be found, so I don't know where that oft quoted figure comes from? 47 calibers is the overall length of the French 15", however.

Re: Gun length in calibers

Posted: Tue Oct 10, 2006 9:44 pm
by José M. Rico
Dave Saxton wrote:For example, Bismarck's 15 inch gun had an overall length of 52 calibers. It's correctly refered to as a 38cm/L52 gun. The distance from muzzle to breach is 48.5 calibers.

That's right.

http://www.kbismarck.org/photos/38cm-SKC34-DE-Rohr.jpg

http://www.kbismarck.org/photos/38cm-SK ... nition.jpg

http://www.kbismarck.org/photos/38cm-SKC34-Rohr.jpg

http://www.kbismarck.org/photos/38cm-SKC34-Munition.jpg
Dave Saxton wrote:There is no internal or external distance of 47 calibers for the Bismarck class 15" anywhere to be found, so I don't know where that oft quoted figure comes from? 47 calibers is the overall length of the French 15", however.
The official German designation for this gun was 38 cm S.K. C/34. There is no mention to the caliber lenght anywhere. However, for some reason the 47 caliber figure appears in many publications:

Jochen Brennecke. Schlachtschiff Bismarck.
Garzke & Dulin. Axis and Neutral Battleships in World War II.
Koop & Schmolke. Battleships of the Bismarck Class.
Elfrath & Herzog. The Battleship Bismarck.

Breyer is the only one (?) who got the barrel lenght correctly.
Rohrlänge (L/52): 19.630 m.
Seelenlänge (L/48.5): 18.405 m.

What do Campbell and Gröner say?

Posted: Tue Oct 10, 2006 11:22 pm
by Karl Heidenreich
So, we have mistakenly stated the lenght of the Bismarck´s guns as a shorter one.

Posted: Wed Oct 11, 2006 5:26 pm
by tommy303
I didn't check Groener, but Campbell agrees pretty much with Breyer.