Thursday 13 November 2014

D-25 One Piece Shell

There are two common misconceptions I keep running into regarding the D-25 gun. One is that its rate of fire was slow because it used a two-piece shell, and the second is that the gun could only be reloaded at a 0 degree elevation angle. Conveniently enough, both are shattered with one document.

"Conclusions on the possibility of using a single piece 122 mm shell in the D-25 gun on IS-122 and ISU-122S guns.

Based on instructions from GBTU, the NIBT proving grounds tested the feasibility of using a one piece 122 mm shell for the D-25 and D-25S guns on the IS tank and ISU-122S SPG, and came to the following conclusions:
  1. Loading the gun:
    1. In the ISU-122S SPG, the gun can be loaded at any angle.
    2. In the IS-122 tank, the gun can be loaded at the following angles:
      1. Horizontal: 360 degrees
      2. Vertical: -3 to +10 degrees
        It is impossible to load the gun when it is elevated more than 10 degrees due to insufficient space between the gun breech and turret ring.
  2. The loading of the D-25 gun with a single piece shell is inconvenient and difficult due to a large size of the shell (1210-1400 mm long), heavy mass (about 40 kg) and limited movement space for the loader. Loading in the SPG is easier than loading in the tank.
  3. The ammunition capacity on the tank is reduced to approximately 27 shells compared to the current 28. In the SPG, the ammunition capacity is increased to 34 shells compared to the current 30.
Based on these results, GBTU considers it unreasonable to switch to a single piece shell for the 122 mm D-25 gun in the IS-122 tank and ISU-122S SPG for the following reasons:
  1. The rate of fire is not increased, as it is more difficult to load a single piece shell. It is impossible to load the tank gun at an angle of elevation of 10 degrees.
  2. The ammunition capacity of the SPG increases by only 4 shells, and the ammunition capacity of the tank decreases by 1 shell."

20 comments:

  1. "There are two common misconceptions I keep running into regarding the D-25 gun. One is that its rate of fire was slow because it used a two-piece shell, and the second is that the gun could only be reloaded at a 0 degree elevation angle. Conveniently enough, both are shattered with one document."

    I didnt understand that.
    There is no Info on the rof in this document and loading the gun with a one piece shell doesnt make sense according to the data.

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    1. It says loading the gun with one-piece shell is more difficult and slower than with two-piece shell.
      The loading was not slow because it used two-piece shell. Two-piece shell was used to make loading faster and easier.

      Atomic Emu

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  2. I think he means that it was not slow just because it was two piece ammo. It was slow because the mass of the shell in any form.
    -m

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  3. The thing is, as always the site administrator fails to interpret information correctly yet presents his incorrect interpretations/conclusions as factual proof.

    Let's start: 'Loading of the D-25 with single piece ammunition was not faster than 2-piece ammunition, therefore loading of the D25 with 2-piece ammunition was not slow'. There is no logical connection between the two, yet our dear site admin creates one.

    One could argue that the D-25's slow rate of fire wasn't purely due to 2-piece ammunition, but this document provides no such evidence. It only states that single piece ammunition wasn't feasible, in part because it didn't lead to faster reload times.

    The only thing one could deduct from the document is that due to size and weight of the 122 mm round, 2-piece ammunition was considered more favourable.

    One could then perhaps argue that the D-25 was slow to reload because it required 2-piece ammunition. Even though there's no such strict requirement as single piece could be used, it just didn't have any benefits.

    The site has a lot of useful information, but one would be wise to (mostly) ignore the admin's interpretations/conclusions as they are often incorrect and unsupported by the very 'evidence' he provides.

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    1. I'm impressed with the mental gymnastics you've gone through to come to the exact opposite conclusion from the one stated in the document.

      As for the rate of fire of the gun, it achieved up to 6 RPM, as much as the King Tiger did in Soviet trials. Whether or not this is "slow" is up to your interpretation.

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    2. "One could then perhaps argue that the D-25 was slow to reload because it required 2-piece ammunition. Even though there's no such strict requirement as single piece could be used, it just didn't have any benefits."

      Maybe it is you who should learn to read, because the document says right there that loading a 1-piece shell is more difficult than a 2-piece shell

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    3. Hello Daigensui.

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    4. Maybe it is you who should learn to read, because the document says right there that loading a 1-piece shell is more difficult than a 2-piece shell

      Really? Let's see:

      "1.The rate of fire is not increased, as it is more difficult to load a single piece shell. It is impossible to load the tank gun at an angle of elevation of 10 degrees."

      It clearly states the rate of fire is not increased, which is not the same as 'rate of fire is decreased'. Keep in mind that the IS has a single loader, who would need load both round and charge one after another. This normally would take longer than loading one piece. But as that single piece is larger in size and heavier, the increased handling difficulty negates the gain.

      And Peter, can you provide a source which states ROF for IS at 6? Even the field gun is mainly listed at 3-4 so it seem unlikely that a single loader within the cramped IS turret would be able to achieve a higher rate of fire.

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    5. "As for the rate of fire of the gun, it achieved up to 6 RPM, as much as the King Tiger did in Soviet trials. Whether or not this is "slow" is up to your interpretation. "

      Sorry but the IS-2 with the D-25T could never archive 6 RPM in combat. The shell was around 25 kg compared to the german 10kg lightweightof the TK(!) The IS-2 was also very compact and had even less room than the KT, its very unlikely that the IS-2 had 6 RPM. Right, Kontin's loading assistance arm...

      Tell me, why they don't take that Inovation into IS-3 and further Series? Why does they still have low firing rates of 2-3 RPM? In you entire blog you only quoting a dubious statement, without any schematic, document references or fotographs. That mystical loading assistance seems to be top secret, not even Zaloga is aware of it, after more than 25 years digging throught Soviet Archives.

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    6. The IS-3 had a technical requirement of 2-3 RPM. On average, the rate of fire was 3.6 RPM, with the actual reload process only taking 9.5 seconds. This is from a Tekhnika i Molodezh article, which Zaloga is no doubt aware of.

      As for the rate of fire of the D-25 reaching 6 rounds per minute, I certainly do no such thing. I have given the sources where this figure is encountered. One was CAMD RF 38-11369-1, one was a document that I do not have a scan of, but is typed up at another site: http://tank.uw.ru/archive/perepiska/doc2/.

      As you can see, documents-wise, my statement of a D-25 that fires 6 times per minute can be made with some confidence.

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  4. With Confidence? Don't make me laugh! Keep harm your credibility with such irrational intoxication. Even Zaloga may have a good laugher over you now.

    Its funny, the ever so mighty Soviets with all their efforts, are unable to handle the 10 kg lightweight shell of the KT (6 RPM), but their freaking 23 kg two piece shell with that mythical loading assistance could archive confidently 6 RPM.

    If Kotin's loading assistance arm was such an god given Innovation to improve the comfort of the loader and firing cycles, I'm sure the Stavka wouldnt take off the chance to improve further tanks with it. Its just mysterious that outside the IS-2, none of the further tank developments being equipped with it.

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    1. Apparently two separate archive sources don't instill confidence in you? Unfortunate. Also did you miss the part where the IS-3 exhibited a similar rate of fire?

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    2. The funny thing is, there's an older article here in which you link to the very same CAMD document. In which the 6 rpm is attributed to the D-25 in an SPG, not the IS-2. Really?

      Your second 'source' is in Russian so I had to resort to Google translate: "Recent tests have given ANIOP'e rate of 4-6 rounds per minute - the results are good."

      No idea what ANIOP means, but 4-6 rpm translates to 6 rpm?

      Like I said, you are as biased as all those German fan boys and cherry pick whatever information fits your biased, subjective opinion. It's sad really, you've put together a very interesting site full of useful information but completely ruin it by adding your own personal, horribly biased and utterly incorrect view on everyone.

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    3. ANIOP is an artillery proving ground. I never said the IS-2 had 6 RPM. I said the gun did. If you want to accuse someone of being "horribly biased and utterly incorrect", at least bother reading what they wrote first.

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    4. But you compare it to the rate of fire of a tank, The Tiger II:

      "As for the rate of fire of the gun, it achieved up to 6 RPM, as much as the King Tiger did in Soviet trials. Whether or not this is "slow" is up to your interpretation."

      So stop comparing apples and pears then. Rate of fire of the 8.8 Pak 43 was 20-25 rounds, rate of fire for the SPG Jagdpanther (while admittedly difficult to get any accurate info on) around 6-10 rpm while maximum rof for the Tiger II at times is given at 8 rpm.

      Once again it is shown you will simply pick whatever fits your predefined opinion and ignore the rest, while (intentionally) mixing up the numbers.

      Grab the maximum rof from either a field gun or SPG (4 - 6 magically becomes 6), and compare it to the nominal rate of fire of a tank to try and prove something.

      Compared to the 8.8 cm PaK 43's rate of fire of 20 - 25 rpm, that 6 rpm indeed is very slow. Is it meaningful to compare? Not really.

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    5. 4-6 is up to 6, no? King Tiger achieved up to 6 too. You initially stated, in your stream of logic that any contortionist could be proud of, that the two-piece shell made the gun slow to load. Nobody was talking about IS-2s or ISU-122s. And then you accuse me of bringing up unrelated guns...and start talking about the Pak 43. Why? It's not even mounted in an armoured vehicle.

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    6. "ANIOP is an artillery proving ground. I never said the IS-2 had 6 RPM. I said the gun did."

      Never? Now you are lying on straight face! I qoute yourself on WT: http://forum.warthunder.com/index.php?/topic/189095-ww2-tanks-v-modern-tanks/?p=3641911

      "The use of two pieces was to accelerate the rate of fire. Under Soviet style conditions (including aim adjustment and shifting targets), the King Tiger achieved 5-6 RPM. The later model IS-2 achieved 4-6 RPM. There was no noticeable advantage in rates of fire. "

      Under Soviet style.. they can magically handle 25kg ammo but not that tiny lightweight 12kg of the KT with even much more comfortable motion space for the reloader as the cramped IS-2 provide. Funny thought, even Zaloga contradict your arrogant shoutings:

      "The most serious disadvantage of the IS-2 was that its small internal size permitted stowage of only 28 rounds of ammunition, and these were of the split type (=two pice) which slowed the rate of fire."

      Ridiculous not? But go ahead and keep misleading others!

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    7. I already told you the documents that I got this information from. Zaloga's data comes from the Soviet standard of using the average of all ammunition racks in a vehicle. Yes, the number is going to be a lot lower in this case. I pointed this out in my KV-9 article where the shells are loaded as fast as 12 seconds (5 RPM) but the ROF overall is recorded as 2 RPM.

      As far as Zaloga's claim that the two-piece ammunition slowed down the rate of fire, I again refer you to the document in this article. It is unambiguously stated that a one-piece shell is more difficult to handle than a two-piece shell.

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    8. >Under Soviet style.. they can magically handle 25kg ammo but not that tiny lightweight 12kg of the KT with even much more comfortable motion space for the reloader as the cramped IS-2 provide. Funny thought, even Zaloga contradict your arrogant shoutings.

      Here's probably where they lost out: Though the 88mm round probably did make it into the breech faster, one disadvantage of the German aiming system is that it's not very fast. The Soviet (and also American and a lot of Brit) system is line up in azimuth, raise gun to proper elevation line, fire. The German system is line up, turn some little knob to lower the set of triangles the proper amount for the range, go back to raise the gun to bring the triangles back on target, fire. If the Soviet standard requires re-aiming rather than throwing shells out as fast as you can, the extra aiming time can easily lose them enough seconds to make up for the difference in loading time.

      There *is* some easily verifiable evidence that the Soviet ROF standard is tougher. The most common quoted rate for a Soviet autoloader tank (T-64, T-72, T-80) is 7-8RPM, or 7.5 second per shot. But if you look at the autoloader cyclogram (at the below link), the actual loading time is under 6 seconds, or even less (about 5) in sequence mode. So the claim that the Soviet standard includes some aiming time seems reasonable.
      http://fofanov.armor.kiev.ua/Tanks/EQP/al-80.html

      >most serious disadvantage of the IS-2 was that its small internal size permitted stowage of only 28 rounds of ammunition

      Zaloga is a decent enough author, but he has done research from a long time back when all he had to go with is rumor, common opinion rather than source documents and tests. He doesn't necessarily re-verify every last position as he writes things.

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    9. I'm rather late, but I would like to add that KwK 43 rounds are not small. The "88mm" caliber gives a very false impression of its size. Total length is barely 5cm shorter than 122mm single piece shell, and it is in fact wider than 122mm shell and shell casing. Dimensions are 88x822mm with a 146mm base diameter, necked down to 88mm only at the end of the case. The case itself is very large. 122mm shell casing is barely wider than the caliber of the shell itself, as it is a straight-walled case, no bottlenecking.

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