Monday, 2 April 2018

OBM-43

"To the Chairman of the NKV Technical Council, comrade Satel
To the Chairman of the GAU Artillery Committee, Lieutenant-General comrade Hohlov
To the Head of the NKVD 4th Special Department, Commissar of State Security comrade Kravchenko

October 2nd, 1943

NKV special telegram #5014 sent on September 24th of this year tasked NKV OKB-172 and Molotov factory #172, as instructed by the People's Commissar of Armament and GAU Chief, to produce an SPG with a 122 mm gun that fired a 25 kg shell at 1000 m/s.

Treating this task as high priority, OKB-172 completed this task early, and presents it for your review.

The following was established as a result of completion of the draft project.
  1. The objective of creating a 122 mm SPG with a muzzle velocity of 1000 m/s is attainable by means of equipping the KV-14 with a new barrel to replace the model 1937 gun-howitzer and using a one-sided hydro-pneumatic balancing mechanism.
  2. Since the power of SPGs is constantly increasing, you may be interested in the proposal of installation of the OBM-43 gun barrel that fires a 43.5 kg shell at a muzzle velocity of 880 m/s instead of the 122 mm gun with a muzzle velocity of 1000 m/s, as this increases the power of the SPG by 33.5% and improves the effect of the HE and concrete piercing power of the shell.
    This solution not only introduces a more powerful gun, but uses the same ammunition in the SPG and the towed gun, which significantly improves the production and use of these weapons.
Attached is the comparative data of the KV-1 SPG with the OBM-50 project.

Characteristic
Unit
KV-14
OBM-50
122 mm gun
152 mm gun
Caliber
mm
152.4
121.92
152.4
Shell mass
mm
43.5
25.2
43.5
Range at 22 degrees elevation
km
12
21
18
Penetration at 1500 m

At 0 degrees
mm
-
195
195
At 30 degrees
mm
-
160
160
Maximum gun elevation
degrees
22
22
22
Horizontal gun range
degrees
+/- 7
+/- 7
+/- 7
Ammunition capacity
rounds
16
16 (38 with converted fighting compartment)
16
Rate of fire
RPM
1.5
2
1.33
Mass of the SPG with gun and ammunition
tons
47
48
48

Having presented the draft, OKB-172 continues work on the project, which will allow OKB-172 to immediately begin working on blueprints upon receipt of your conclusions.

OKB-172 Chief, Lieutenant-Colonel of State Security, N.A. Ivanov"

19 comments:

  1. Guessing this is the at least conceptual ancestor of those monster BL-8 and -10 guns they tested on the ISU-152 around the end of the war?

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  2. Soviet domestic ww2 vintage AP shells were not fit for these high velocities. The power of the gun is wasted.

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    1. Seems pretty fit to me: http://4.bp.blogspot.com/-UGMZDf2Raks/Uv40IkpI24I/AAAAAAAACgQ/LoULsTdAue0/s1600/BL-8-3.jpg

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    2. 150mm @30°- Considering that it´s a 150mm gun with 900m/s velocity that´s very disappointing.
      A high quality AP will defeat 150mm @30° readily from a 740m/s gun, so 900m/s velocity is wasted.

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    3. So if the shell shatter at higher velocities and dont penetrate, it means no more demage? Here you have AP shell stuck in Ferdi armour. Yes there is some side effect, plus area of the one bolt hole was hit but for gods sake, that 122 APHE trumped over all capped projectiles in overall performance against Tiger II.

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    4. That's not maximum penetration, literally just a random photo. Also you don't even know the range the tests were peformed at, so you don't know the impact velocity. What happened to your usual wailing of "you don't know everything about the test, you can't make any conclusions"?

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  3. Shatter means among other things, that the explosive cavity will compromise it´s rigid confinement. It may thus be either blinded (losing HE-effect entirely) or suffer deflagration (blow out) or, at best, a low order explosion, typically only 1/3 as powerful as a high order explosion would be.
    Yes, shatter can also increase damage, particularely to the impacted plate because shatter regularely prevents a ductile failure mode of the plate and inhibits ricochet at extreme obliquity. However, shatter will considerably reduce penetration compared to unshattered projectiles except at very acute obliquities.
    The BL8 tests are obvious comparisons: They required a high velocity for a disproportionally low penetration. The 150mm Pzgr L/3.7 APCBC-HE penetrates rliably (5 out of 5 times) 150mm RHA at 30° and 700m/s or 200mm at 0° and 690m/s. Penetration graphs of which I posted here:

    [url]https://forum.axishistory.com/viewtopic.php?f=47&t=233636[/url]

    A 122mm APCBC would be superior to the 122mm APBC. Such a projectile was not available 1945 but subsequently was reverse engeneered and eventually adopted for service in the soviet Union in the early 1950´s for high power guns under the designation BR-471D and BR-472.

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    1. I'm not entirely sure what relevance the workings of the bursting charge, which is all about the behind-armour effects, have to do with the supposed "waste" of the gun's power, which presumably mostly concerns penetration... doubly so as with forty-odd kilos of hot shell plus sundry armour fragments abruptly entering the interior at high velocities I daresay the difference would be quite academic insofar any occupants are concerned.

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  4. If shatter deletes an important aspect of lethality of the round it carries significance. The 15cm ML-20 AP shells were found satisfactory (no shatter, marginal projectile break up) when attacking 120mm plate at 30° (0.8cal for the 15cm projectile), though the fuze was not satisfactory in producing high order detonation reliably behind plate. Tests against 150mm plate were conducted with blind projectiles (inert filled) because they only considered penetrative aspects. Yes the projectile would have a tremendious wrecking effect on any structure hit, but any other shells in this size class would have, too.
    0.8cal/30° isn´t a much challanging requirement. Even 1.0cal/30° woudln´t raise any eyebrows.
    The late model, 75mm Pzgr39/42 stayed intact at 2.67 cal plate at 30° (german tests vs 200mm plate) and 1.76cal plate at 45° (US tests vs 132mm plate) with no projectile damage other than stripped nose covers and driving bands -in intact condition fit to burst. Such high penetrative performance -while keeping the full lethality enevelope- was only possible because the projectile didn´t broke up prematurely (unlike all the 90mm M82, 90mm M77 and 90mm T33 in the US tests, which the russians admired so much for their robustness).

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    1. "Wasting" the ultimately rather secondary effects of the bursting charge is rather different from "wasting" the altogether much more important penetrating power of the shell, though, and I'm pretty sure you haven't exactly demonstrated the latter was the case. The former doesn't do squat without penetration in the first place and was eventually dropped from AP shells altogether (partly due to the switch to subcaliber penetrators which can't fit one anyway, but the Brits at least had binned it already by the war). IIRC they more or less universally also had persistent issues with fuze reliability.

      Not that you wouldn't want it to work properly if you've gone to the trouble of including it in the design to begin with, of course, but it's hardly a *critical* aspect - doubly so on a projectile boasting as hideous kinetic energy as this. Hell; the thing could probably have KO'd tanks just fine by the secondary effects of hypothetical nonpenetrating hits already.

      Short form is the whole tangent has the whiff of a red herring about it.

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  5. Shatter DOES reduce penetration -and considerably so except under acute obliquity. Attempting to claim otherwise only underlines a lack of knowledge in basic penetration mechanics, an attitude of whishful thinking or lack of access to prooving ground data. When 45mm soviet domestic APBC was test fired vs high hardness, 8S plate, the limit velocity of the (always) shattered projectiles was 720m/s (PSP limit at 0°), K=2725. When they tested 5cm Pzgr39, which stayed intact suffering no shatter, the limit of PSP against the same plate and obliquity was found to be only 360m/s (K=1600), which was even lower than the 76mm domestic AP limit velocity for this thickness. And mind, its from soviet comparative trial data.
    Soviet calculated performance for OBM53 (900m/s) (presumably at standart De Marre K=2400) was 202mm penetration 1500m:
    http://tankarchives.blogspot.de/2013/03/penetration.html

    203mm plate, BL-8, 0° 50% probability of holing limit (velocity unknown):
    http://tankarchives.blogspot.de/search/label/BL-8

    If You hold it for probable that the soviets tried to fit calculated and tested performance for the projectiles they knew best (their own domestic projectiles and guns) from the two soviet documents then it follows that 200mm @0°penetration at 1500m from a 152mm gun and i.V.900m/s.
    Penetrationwise, this is a low performer considering the momentum generated by the powerful gun, only explainable by inferior projectile quality. The performance for a 150mm gun L/60 firing at 960m/s where 200mm RHA @0° would be reliably penetrated reaches out to 4500m. The penetration definition was more strict in Germany than it was in the SU.
    Actually, the the 200mm @0° penetration at 1.5Km falls in between those of the 88mm KWK43 and 128mm PAK44, both of which are smaller weapons fitted with a superior projectile quality.
    Reduction of HE effect by shatter happens to augment the reduction of penetration performance by shatter. And mind You, the german superior projectile quality occured despite a considerably leaner alloyed shell steel. That´s good mettallurgy on their part.

    The brits deleted HE filler when the NPL realized that the german spaced plate of PzIII /-IV turrets caused premature explosion and therefore no holing of the turret front plate due to HE activity.

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    1. Again, you have absolutely no information on what velocity the tests were performed at, but somehow you are absolutely certain that they mean that Soviet 152 mm projectiles were inferior. Meanwhile, you're blasting the British analysis of German armour, even though the conclusions they make are based on a whole lot more data than you're working with here. This is a common factor with you. You completely disregard the research done by actual scientists and then take your own intuition for fact.

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    2. Seeing as how the numbers are in any case *much* higher than with the gun-howitzer of the same caliber - what a surprise, eh? - I'm not exactly seeing where you think you can get away with your claim of "waste of gun power"... nevermind now the incidental side benefits of higher muzzle velocity.

      Also last I checked the Brits stopped putting bursting charges into their AP well before they even got into shooting matches with ze Germans.

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  6. Peter, You disregard soviet primary sources like the firing trials of 5cm Pzrg39 vs Your so much vaunted 8S high hardness armor steel when they don´t fit Your agenda. Fact is that the soviets stabilizted their projectile design on a projectile-plate relationship as expressed by De Marre K=2400, which would apply only for high quality test ammunition. Unlike the germans, they did not require their projectile to stay intact or to facilitate complete penetration consecutively. When they tested german post 1942 service AP, they found it to be able to perforate their plates at much lower velocity and much lower De Marre K factors than their domestic projectiles. Post ww2, they adopted these german projectile designs for their own, and they probably didn´t do it because they admired anything german, they did it because these projectiles did not break up as readily as did their highly ineffective domestic designs.

    soviet domestic AP vs 45mm 8S at 0°:
    https://imgur.com/a/1iMED
    german 5cm Pzgr39 vs 45mm 8S at various obliquities:
    https://imgur.com/a/g3bTr

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    1. Right, so you go back to your blanket "everything Soviet is bad, everything German is good" theory as always.

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    2. All of this does fuck-all to rescue your original claim of, quote, The power of the gun is wasted, unquote, which is complete BS right in the face of it. I'm personally plenty willing to entertain the notion that there was room for improvement in Soviet shell design and/or metallurgy already based on their own testers' comments on L-L shells; that just means *the gain was not as great as it could have been* which is a different matter entirely (and would have been a cold comfort indeed for anyone at the receiving end of this thing).

      There seems to be a fundamental error at the core of, well, basically all the arguments you're making on this site - you're confusing "not as good as it could be" for "no good at all" and proceeding from there.
      Given your tendency to only do this with Soviet stuff and conversely knee-jerk blanket denials of well-attested (and mostly resource-derived) QA problems on the German side of things one might almost be inclined to suspect a degree of bias at play...

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  7. there is no theory. I just make observations. Apparently, You decide which observation one would want to speak about, that´s selective perception.

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    1. I'm pretty sure I call out your "observations" pretty consistently. I'll try to be more thorough in the future.

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