Question For Bill Jurens & All Re Barrel Length

Warship design and construction, terminology, navigation, hydrodynamics, stability, armor schemes, damage control, etc.
BuckBradley
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Question For Bill Jurens & All Re Barrel Length

Post by BuckBradley » Thu May 30, 2019 7:06 pm

Hi all:

I have to admit that I was ruminating upon tanks when this question popped up in my mind, but I imagine it is at least somewhat translatable to battleships and to the extent that it is not that might be interesting to note.

One of the means whereby gunmakers have increased penetrative capacities is to increase the length of the barrel. The 75mm L/70 is going to penetrate a lot more armor than the 75mm L/35. The 12" 30 cal" is going to penetrate less armor than the 12" 45 cal. Etc.

Question being, is there (aside from unweildiness) a point of diminishing returns? Some point at which "too long" a barrel might actually decrease accuracy or degrade performance? One simplistic thought--amounts of powder being equal, wouldn't the friction imparted by a long barrel eventually cancel out the virtues of permitting the shell to be in the barrel with the powder gases still expanding?

Of course the powder amounts would not be equal, would they.


To what extent can lengthening the barrel of a relatively small caliber gun compensate for BEING a realitively small calibre gun? Could I turn a 37mm into a Tiger-killer just by making the barrel long enough and putting more powder in the cartridge?


Thanks in advance,

BB

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marcelo_malara
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Re: Question For Bill Jurens & All Re Barrel Length

Post by marcelo_malara » Thu May 30, 2019 10:37 pm

I think that there is a limit in the amount of powder you can burn in a barrel. If you make an extra long 37 mm barrel you will need more powder to propel the bullet, but that powder will burn at the same speed that in a short barrel, so the pressure would be higher. You can use a slower burning powder, but there would be a limit in the slowness of the powder too.

Interestingly, someone developed an experimental long barrel to overcome all this, it had several chambers perpendicular to the barrel along its length. The charges were fired in turn as the bullet passes each chamber. Don´t remember who did this.

Another question comes from the thermodynamics. The internal surface of the barrel varies linearly with the caliber, but the internal volume varies with the square of the caliber. That means that the larger the caliber, the greatest the internal volume in contact with the surface, so a burning powder charge losses less heat and the gun is thermodinamically more efficient. A black powder musket, 58 caliber, would have a barrel 1 metre long (66 calibers), but a naval gun of the period would be about 15/20 calibers long.

ede144
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Re: Question For Bill Jurens & All Re Barrel Length

Post by ede144 » Tue Jun 04, 2019 4:53 pm

@marcelo

https://en.wikipedia.org/wiki/V-3_cannon There you can find some information about multi-charge guns

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marcelo_malara
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Re: Question For Bill Jurens & All Re Barrel Length

Post by marcelo_malara » Wed Jun 05, 2019 12:31 am

Thanks!

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marcelo_malara
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Re: Question For Bill Jurens & All Re Barrel Length

Post by marcelo_malara » Wed Jun 05, 2019 3:08 pm

Interesting, so much effort to obtain 1500 m/s, what is about the same as an APFSDS anti tank projectile.

Regards

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