7,5 cm Kwk/StuK/Pak 40 Firing Table Data

[Yoozername]

My question was why are you deriding amizaur's work? He isn't even here to discuss it? So, using your 'manners rules', that would make you a bit of undesirable formulator of an even lower class.

And, yes, castings not only varied, they were allowed to. That is, the specification was looser. And, as the US Army found out with its sherman tanks, while castings had advantages, they also had issues with them.

[Stiltzkin]

My question was why are you deriding amizaur's work? He isn't even here to discuss it?

I am not "deriding" it, his work is very useful as any contribution is. I just never accept the work of "amateurs" as absolute, being 100% accurate. Not even primary sources as the individual who wrote it at that time might have been in a stressful situation - simply, human errors are present everywhere. Methodologies can be flawed or misunderstood.
We are looking at values, deriving crew behaviour and actions from this and how they operated and fought is rather difficult. Uparmouring a tank does not necessarily make a tank "technologically superior", especially if you neglect its fighting abilities, visibility or use inferior steel quality. It has diminished returns. Theory and praxis are two different things.

Cast armour lowers manufacturing time and above of a thickness of 80mm it starts to approximate the value of RHA by 87% (in theory) - to quote Rexford Bird.

[Yoozername]

Rexford Bird was a civil engineer.

Thanks for the laugh. 100% accurate? And you fancy yourself a 'statistician' (or whatever you fancy yourself)? Sorry, being an actual 'technical person', I find you amusing. And, as far as 'staying on topic'....I will quote you...

We are looking at values, deriving crew behaviour and actions from this and how they operated and fought is rather difficult. Uparmouring a tank does not necessarily make a tank "technologically superior", especially if you neglect its fighting abilities, visibility or use inferior steel quality. It has diminished returns. Theory and praxis are two different things.

[David Thompson]

Yoozername -- Please avoid uninformative (viewtopic.php?p=2084003#p2084003) sentiments when posting.

[Mobius]

Please include who you are quoting as I can't follow and it seems a private sub-thread.

[Yoozername]

From...The Russian Battlefield website...

In the beginning of 1944, an attempt was made to improve the protection of the JS-2 by tempering the front armour to very high hardness. In practice, it led to a drastic increase in the number of components needed for the hull and significantly increased the cost of the tank's production.

In March 1944, firing tests were conducted with a 76.2 mm Gun ZiS-3 firing at an JS-2 tank from 500-600 metres. The tank's armour was penetrated from all sides of the tank. Whilst while most of the projectiles did not penetrate the armour completely, they created major splintering and fragmentation inside the turret. This explains the considerable losses of JS-85 and JS-122 tanks during the Winter-Spring of 1944.

In February of 1944 the Central Scientific Research Institute No.40 (TsNII-40) was delegated the task of researching the armour protection of the JS-2 heavy tank. The research showed that, given the existing shape of the front of its hull, the tank would be invulnerable to penetration by any German 75-mm and 88-mm AP projectiles only if the hull's armour thickness were increased to at least 145-150mm (i.e. an addition of 20-30 mm thickness).

On the recommendation of the TsNII-40, new specifications for armour tempering and a new design for the front of the JS-2's hull were developed. The new hull, with a straightened glacis, preserved the same armour thickness while the plug-type driver's hatch was removed, greatly increasing its protection from the front. The glacis was sloped at 60 degrees from the vertical, which resulted in the German 88 mm KwK 36 gun being unable to penetrate it even at point-blank range when fired at a ±30 degrees angle.

However, the lower front hull armour plate, sloped at 30 degrees from the vertical, remained vulnerable. To increase its slope would require significant alteration to the layout and design of the driver's compartment. Since the probability of a hit on the lower part of the hull was low, it was decided to leave the design unchanged. From July 15 1944, spare tracks were attached to the lower hull to increase its protection. In May of 1944, the UZTM plant started manufacturing the new straightened welded hulls. Factory No.200 began making the new type of hulls from June of 1944, but these were cast, not welded. However, for a while, tanks with old and new hull-types were produced simultaneously.

As for the tank's turret, it turned out to be impossible to increase its armour protection. Designed for the 85 mm gun, it was completely balanced. After installing the 122 mm weapon, the turret became very unbalanced. The Design Requirements intended for an increase of its frontal armour thickness to 130 mm which would have unbalanced the turret even further and would have made a new traverse mechanism necessary. SInce all these changes required a complete redesign of the turret, they were all cancelled.

Nevertheless, the appearance of the turret was considerably changed in the process of its production. The first batch of tanks manufactured in 1943 had a narrow porthole through which the sighting telescope fits. After the installation of the D-25T Main Gun, it became almost impossible to use the telescopic sight, even though its breech was the same as that of the D-5T.

Starting in May of 1944, a new turret with a widened porthole was manufactured, which resulted in the sight being moved to the left. The armour protection of the tank's mantlet was improved and the armour thickness of the sides of the lower hull was increased.

[Yoozername]

While I think that the thread is being driven a bit off-topic, it has been said that the IS-2, or Soviet Heavy Tank Program, was responding to the German Pak 40/KWK 40/StuK 40 weapons. Of course, as the Panther and Tiger guns and Pak 43 became more common, it had to deal with facing those.

It seems the Soviets figured out that cast armor, while seemingly a production shortcut, does need heat work. The US found this out also. Especially when testing cast armor in cold environments.

Also, I believe that Amizaur did his work with this test instrument. I will leave it to anyone that is interested in its specifications and proper usage to read up on it and compare that with Amizaur's work.

http://www.reedinstruments.com/product/ ... ness-gauge

[Mobius]

While I think that the thread is being driven a bit off-topic, it has been said that the IS-2, or Soviet Heavy Tank Program, was
http://www.reedinstruments.com/product/ ... ness-gauge

I bought an ultra sonic device and was going to take it up to the Littlefield collection but alas that was a no-go after Jacques passing. They do work well. Mine up to 203mm.

[Yoozername]

It is probably reading accuracy to a couple millimeters either way. It can be calibrated with a known standard thickness. You can do this with a steel plate that you can use a calibrated micrometer on. The micrometer will be much more accurate than the ultra-sonic device.

[David Thompson]

An off-topic opinion post from Paul Lakowski and a now-unnecessary response from Yoozername were removed as they added nothing of value to the discussion of 7,5 cm Kwk/StuK/Pak 40 Firing Table Data -- DT.

[Mobius]

It is probably reading accuracy to a couple millimeters either way. It can be calibrated with a known standard thickness. You can do this with a steel plate that you can use a calibrated micrometer on. The micrometer will be much more accurate than the ultra-sonic device.

Where are you going to find a micrometer that fits around a turret mantlet? Besides mantlets are often attached to turrets so you can only have access to one side. I think the ultra sonic is accurate to a tenth of a mm. But armor thickness probably varies more than that from tank to tank.

[Yoozername]

No, calibration is not done on a vehicle. You would need a 'standard', or a known measured plate, but a very good substitution is a decent plate and a micrometer that reaches around it...two inches let's say...the micrometer IS already calibrated (from a cal lab), and you can measure the plate and therefore check what the ultrasound device reads. If it has a calibration feature, you can dial it in. It is comparative calibration. Micrometers are more accurate than the ultrasound.

i also have gage blocks and will send them out to be calibrated also.

note; 4:1 is 95% in statistical terms

The standard used in calibrating measuring gages must possess an accuracy greater than a 4:1 ratio over the accuracy of the gage being calibrated. The accuracy of a gage block is typically ±0.000002 inch, and the accuracy of a micrometer is typically ±0.0001 inch.

[Mobius]

Here's a better look at the mantlet of the JS II said to be knocked out by a 75mm Pak 40 with a shot through the gun sight.
http://www.williammaloney.com/Aviation/ ... /index.htm
As found in Berlin.

[Yoozername]

The 'mantlet' is an interesting design. perhaps better described as a turret front assembly. It includes the trunnions, proper mantlet and also the frontal armor of the turret. All held on with bolts it seems and making damaged gun repairs easier. Other pictures show the assembly blown off the turret as these bolts must have sheared from an internal explosion. An interesting feature is that the Soviets had a hard rubber 'isolation mount' under the mantlet.


The lower hull would be vulnerable to pak 40 and KWK 40/Stuk 40 weapons. A penetration there would kill/incapacitate the driver and there was propellant right behind him. The 12.2 cm projectiles seemed to be around the turret. Penetrating the lower frontal hull would result in a projectile course that would 'tick' upwards into the interior of the IS-2. These AFV would be best used at range and using hull down positions to provide overwatch to hordes of charging T34s.

[Miles Krogfus]

When the Germans obtained a Soviet 85 mm Armor vehicles gun models firing table, a 14 page report was issued. Here are 2 pages from it, and a 2 page report on the "new" JS tank: