8,8 cm PzGr 39 Performance

[Contender]

The M4A1 had a 51mm thick plate sloped at 56 degrees. It was cast armor.

To add to this the widely used late M4A1 armed with the 76 mm weapon was 63 mm @ 47° (cast armor).

Also the ~51mm (aka 50.8 mm) Sherman glacis plates were multi-piece & had some cast armor elements:

which later they applied plates over as stop gap measure:

[critical mass]

I have never taken Wunderwaffe serious. From what I can gather, I get the impression that the Prussians and Germans always went for technical solutions to their social problems. This was both, the constituent and the Modus operandi. The function of WW falls exactly here, to keep up social support for a lost conflict.

The pzgr.39 was different. It’s Areal Instrument of warfare, not a vague concept to keep social unrest at bay.

The Germans did use wunderwaffe in a ploy to maintain support for a lost cause, with the V-1 and V-2 being the most obvious examples. But I was never aware that the Prussians had done the same thing. I struggle to imagine what would qualifty as a wunderwaffe. Perhaps the Dreyse needle gun?

Not the WW concept. This fullfills its function best in strongly populist or controlled societies, such as nazi germany (or SU). But the Prussians bought fully into the idea to turn towards technical solutions to adress their social problems (i.e. public baths, railway net, wireless telegraphy, planned long distance zeppelin flights to connect with colonies, etc.).

Anyway. I have been wondering for some time, what kindof protection the different variants of the Sherman tank could offer against 75mm Pzgr 39? Specifically, what kind of protection could the glacis plate offer?

I can´t remember where but I think I have expressed my opinion before. I believe at least the later welded M4 glacis was a sufficiently strong target for the ordinary mass produced (1942-1943) 75mm Pzgr.39 fired from PAK40/KWK40 because it´s sufficiently thick and declined to induce a high probability of break up the shell. Of course, US RHA is softer and less able to damage but we know that it could do so (f.e. 132mm RHA vs 88mm Pzgr.39 trials). Had it not been for the timely update of proof requirements from 30° to 45°, which guaranteed that most projectiles would not break up while engaging such a target, when it occurred on the NW theatre of war, we would perhaps have now a somewhat different discussion on the topic. It occurs to me that the M4 was sort of a timely victim of an ongoing arms vs armor race on the eastern front.

[Avalancheon]

Also the ~51mm (aka 50.8 mm) Sherman glacis plates were multi-piece & had some cast armor elements:


which later they applied plates over as stop gap measure:

Apparently, it was the M4A2 Shermans that had the protruding drivers hood (with vision slots). The glacis plate itself was RHA, but the hoods were cast. This complicated the manufacturing process, and created a ballistic weak spot. This website has more details: http://afvdb.50megs.com/usa/m4sherman.html

''Starting in late 1943 at the Fisher Tank Arsenal, the 56° glacis on the M4A2 was replaced by a single-piece plate inclined at 47° from vertical. The 56° glacis featured protruding drivers' hoods with direct vision slots on early tanks and periscopes on later vehicles, and the glacis plate was composed of several pieces welded together, which complicated production. The 47° plate was a single piece and eliminated the drivers' hoods.''

[critical mass]

Note that there is a ricochet right to the holing perforation on the glacis.

[Contender]

Apparently, it was the M4A2 Shermans that had the protruding drivers hood (with vision slots) drivers' hoods.''

Yes, there were also other variations without the vision slits. I suppose I should point out despite production year claims (production≠ deployment) this & other the multi-plate glacis sherman variations served in large numbers until the end of the war.
random multi-plate shermans with vision slits from 1944:

Note that there is a ricochet right to the holing perforation on the glacis.

Note also the dislodged bolts right underneath....

[Peasant]

I've remade this chart. Click for high resolution images.



Interestingly enough, when we plot this curve and the one from the BIOS report together, they don't overlap. Share your ideas on why this is.

[Thoddy]

Comparative performance of post 1943 and pre 1943 7,5 cm Pzgr

[Avalancheon]

I've remade this chart. Click for high resolution images.

Thats a good rendition of the Durchschlagsleistung from the Lilienthal report. However, its missing the plate hardness numbers on the side.

The 75mm kwk 40 had a muzzle velocity of 750 mts when firing Pzgr 39. According to this chart, it should be able to penetrate the M4A3 Shermans glacis plate out to 100 mt or so?

But then again, American armor was softer than what the Germans used. The 75mm kwk 40 could probably pierce the glacis from a greater distance than that.

Do you know how to convert kgf/mm2 to BHN?

[Peasant]

Thats a good rendition of the Durchschlagsleistung from the Lilienthal report. However, its missing the plate hardness numbers on the side.

I've decided against reproducing the tensile strength scale, because I couldnt think of an elegant way of editing it in with tools Excel provides.

The 75mm kwk 40 had a muzzle velocity of 750 mts when firing Pzgr 39. According to this chart, it should be able to penetrate the M4A3 Shermans glacis plate out to 100 mt or so?

But then again, American armor was softer than what the Germans used. The 75mm kwk 40 could probably pierce the glacis from a greater distance than that.

Do you know how to convert kgf/mm2 to BHN?

You can't, strictly speaking, covert tensile strength(kg/mm^2) into hardness, its like asking to "convert" decibels into meters per second, these are two separa physical quantities.

But there is a relatively simple linear correlation between the hardness and ultimate tensile strength in nichel-chrome steels. One can estimate the equivalent hardness expressed in BHN of a plate by multiplying its tensile strength by 2,911, so the 100kg/mm^2 plate would have BHN of about 291.

As far as I know, increasing hardness offers less benefit as obliquity increases, and a harder plate that was superior at low obliquity to a softer one (assuming that this superiority was not because it damaged the projectile) can become less efficient than a softer one when attacked at high obliquity.

But you're right, the Kwk 40 L/43 should be able to defeat such target at much longer ranges, not because of the difference in armor quality, but because german penetration criteria used here results in a very large dispersion of results, depending on whether or not the projectile remained intact or not. If it broke up, we might see this gun fail even at 200-300m. But this very unlikely since, the US armour of this thickness was much softer than german test plate this data was complied from(260BHN vs 320BHN). You can see in this thread viewtopic.php?f=47&t=247739 that to offer complete immunity(G(s) limit) against an intact 7.5cm pzgr.39 fired from Pak 40 at 100m a thickness of up to 100mm/46° is required.

This table here reports the Navy limits for US 90mm T50 post war APCBC projectiles(among others). Using the BL of 2216fps against 3"/45° as a reference, I estimate the 50% limit for Sherman UFP vs 7.5cm PzGr.39 as 652m/s(approximately). Depending on the muzzle velocity it was fired at(750..790m/s) the equivalent distance would be between 900-1200m.

[Peasant]

This document here, suggests a model for estimating the performance at obliquity of AP shells of German design under conditions that they remain intact.

Using the 30° values for intact shell as the reference, I estimate the following critical velocities for 7.5cm PzGr.39 against late Sherman hull: G(s) = 615m/s, G(d) = 670m/s. The relative distances for v0=790m/s are 1550m and 1050m. These results fit very well with Yugo tests placing the 50% limit at 1200m.

[Thoddy]

A high quality Pzgr.39 was capable to perforate roughly cal/RHA plate at 45 to 50 degrees intactly ft to burst. However, a poor quality shell would break up at 40° or even less. There is a scatter in projectile quality caused by tolerances in heat treatment of the individual sub contractors. The new proof specifications could only be obtained by applying much tighter heat treatment tolerances, of the AP-cap, the shell body and the fuse threads. The alloy composition of the shell steel just provided potential hardenability, it was the subsequent heat treatment, which transformed the potential into discrete physical properties.

Its somehwat the progress of metallurgical skill allowing improvements. The first Pzgr.39 were high quality if made by special labs in low quantities, for research purposes. It required the welded on nose tip to make mass production of the product feasable. By late 1942, Döbener Gusstahlwerke finnished its work on heat treatment and research of monobloc Pzgr. 39 shells with the same or higher quality than the welded on tipped versions. This was applied throughout 1943 in mass production over a wide scale.

with regard to this study, its remarkable that the performance of the projectiles was increased despite not changing projectile geometry. Only optimisation of alloy composition / optimisation of heat treatment/hardening/ hardness distribution. They checked composite projectiles(two pieces welded togehter) as well as homogenous ( one piece) projectiles. in the end No difference in Performance between composite and homogenous projectiles.

The earlier 7,5 cm Pzgr 39 were typically hardened at the tip and upper ogive to about 59 Rc gradually decreased to About 55 RC over the ogive/ and Rc 52 in the core, whilst for the later projectiles a hardness of up to Rc 63 at the tip and upper ogive was found to be optimal for overall performance.(Core hardness Rc 59. same hardness distribution for cap). as the caliber increases somwhat lower hardnesses wer optimal

To hard projectiles tend to cause earlier shatter on impact due to excessive brittleness.
lower hardness projectile tend to shatter by deformation->cracks->shatter during the penetration process.

Abvout 700 test shots were carried out.

As far as i can see 63 Rc is also considered as optimal also fo modern non deforming projectiles

After complete heat treatment new hardness distribution as following

comparision of projectile performance of different heat treatments (old / new)

Results for to hard

[Contender]

Old news but, I think still worth posting here:
Ammunition types for 8,8 cm KwK 36:

[Peasant]

Wow, what's this: 780m/s velocity for the AP shell? Interesting. Then perhaps the much quoted figure of 773m/s is the velocity at 100m after all.

[Mobius]

Wow, what's this: 780m/s velocity for the AP shell? Interesting. Then perhaps the much quoted figure of 773m/s is the velocity at 100m after all.

The FES weight was 10.0 kg. The 773 m/s AP was 10.2 kg. Though I haven't found the firing table for it.

[Contender]

Stupid question: is Pzgr 40(w) iron-core?