Why are modern tank cannons of the 120 mm caliber

Ideally it's not supposed to come out the other side: doing it that way means there's little energy transferred to the target and doesn't guarantee a kill shot.
If it puts a hole in the target and doesn't come out then that means the (not inconsiderable) energy of the shot has been deposited into the target. And that energy will find its expression in internal destruction.

 

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If there is ever a zombie apocalypse...I'm headed to Dy's house.

 

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It seems to me the ultimate kinetic weapon would be the railgun. I don't see why a tank couldn't be fitted with one. I can just imagine a DU traveling at many times the speed of sound. There isn't much that could stand against it.

Navy Sets World Record With Incredible, Sci-Fi Weapon

Read more: http://www.foxnews.com/scitech/2010/12/10/navy-railgun-shoots-bullets-electromagnet/#ixzz1cPkee1lW

 

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Power generation/ size, for one.
The required energy is feasible from an on-board plant, but anything small enough to fit an AFV has a recharge time that militates against the required rapidity of fire (6-10 rounds per minute).

Um, current APFSDS (DU or not) shot travels at a minimum of 1500 m/ sec, and approaches 2,000 m/ sec in more modern (especially the German 120 L/55 gun) weapons.
That's (roughly) Mach 5 to Mach 7.

In fact the current equation (unclassified) used to calculate penetration assumes that all rounds will impact, regardless of range, at a speed of at least 1500 m/ sec.

 

Hmm, okay.
A bit more on why 120 mm rounds are (currently) the preferred limit.
The calibre dictates the overall size of the complete round (as should be obvious). A larger calibre requires a larger round (longer and larger diameter casing).
That size dictates the turret size:-

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There must be enough room in the turret for the round to be presented to the breech (upper diagram Dimension A) and also enough room for the gun to recoil without hitting any internal components (lower diagram Dimension B) with enough clearance for the ejected case to be thrown clear (lower diagram Dimension C).

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This is hard enough, BUT, this must also hold true for a gun at full depression without hitting the turret roof (upper diagram) and full elevation (lower diagram) without running into the turret ring.

More to follow...

 

BAh...Just add tonnage.

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I bet shit would change damn quick, if a real conventional war broke out. Tanks are useless nowadays. I bet powered infantry armour would get invented withing a few months of the first clash (should nuclear exchange be somehow averted - see what I mean...wtf do they waste time with this shit anymore?)

 

From the above it can be seen that the size of the complete round dictates turret ring size and turret height. These have knock-on effects:

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It should be obvious that turret ring size has an effect on vehicle overall width from the lower diagram...

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But it doesn't stop there.
The turret height PLUS the height of the required crew (I believe that Western designers try to accommodate 95% of possible heights, the fUSSR used to deliberately assign short people [5' 5" max IIRC) as tank crew) PLUS turret basket clearance gives the overall vehicle height.

And more...
The turret ring diameter dictates minimum vehicle width, which in turn dictates track centres (annotated "C - See Note"). This figure goes into dictating the overall (max/ min) vehicle length since the ratio of track length on ground (L - See Note in the first pic in this post) divided by track centre size should be around 1.4 (some variation allowed): much more than this and the vehicle becomes unstable in turns, much less and it has difficulty turning.

Thus: the larger the round used the larger the vehicle must be. And then you have a choice: large-lightly-armoured vehicle (what do you use it for?) or large properly-armoured vehicle (which is therefore heavy and you have logistic/ transport problems)?


(All drawings copyright ME!)

 

Nice drawings. May I ask how you know so much about tanks? Did you use to drive one or something?

Also, why does this forum not have a military sub-forum? You'd make a great moderator for it.

 

LOTS.
I'm currently (hence the diagrams) in the process of "(re) writing" Ogorkiewicz's Technology of Tanks as a hyperlinked e-book.

No, I'm just a (very) technical geek.

Been mooted many times.

Been there, done that.

 

Good project. Sounds time consuming? What's your estimated completion time?

That was a given.

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I would have voted for it.

Another forum?

 

Maybe before I die.

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It's something I pick up and add to when I'm in the mood.

Human science, here.

 

There was not a single part of that statement that was even close to correct.

 

Fed I'm just gonna say fuck you since, I don't see a rebuttal.

http://en.wikipedia.org/wiki/BGM-71_TOW

 

But your only talking about ordinary tanks. Before we have another major war effort we might have the following Laser tanks rolling off the assembly line.

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I'm sure any decent computer controlled defense wouldn't let anything as crude as a missile get through.

 

Nietzschefan if shit were music you would be an orchestra.

http://en.wikipedia.org/wiki/Trophy_(countermeasure)

 

There's also the maintenance/reliability issue. Railguns are great for firing one round - and then needing to be refurbished before they can be fired again. If people can get them to the point where there's no arcing degrading the rail surfaces, overcome the various heat problems, etc. then they're potentially pretty cool for certain applications (mostly stuff on ships, where you already have a power plant on board anyway).

 

Abso-fragging-lutely.
They're still a way off even for use on very large platforms (warships) that have the facilities to do a "barrel change". AFVs are a no-no for the near foreseeable future.

 

It all comes down to materials, if in a month a new alloy is discovered that is to superconductors and whatever category this falls in is to titanium-nickel was to jet engines then maybe we can revise that estimate a little.