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

[Yoozername]

These cutaways are from actual rounds.

[critical mass]

Yes, that´s how the cap should look like. The british report has the naval type cap instead (also fitted on 88mm Pzgr39). However, the 75mm Pzgr39, 50mm Pzgr 39, 105mm Pzgr 43 and 128mm Pzgr43 specified the thicker, Army type percing cap.

[seppw]

Yes, that´s how the cap should look like. The british report has the naval type cap instead (also fitted on 88mm Pzgr39). However, the 75mm Pzgr39, 50mm Pzgr 39, 105mm Pzgr 43 and 128mm Pzgr43 specified the thicker, Army type percing cap.

Was the naval type cap more effective against real cementated armor than the army type which looks like it's much easier to manufacture?
If not, what was the idea behind the naval design?

[critical mass]

The shape of the cap itselfe is only of limited importance to penetration. However, the weight, the hardness and the depth in front of the projectile nose created by the cap and even it´s attachment to the projectile nose are significant factors.
What a cap intends to do is to keep the projectile nose intact and thus, to allow deeper penetration because the projectile is concentrated and does not undergo a change of shape (=broken up). This, of course requires a strong projectile nose design to be present, too.
A deeper cap would smash a cap with pit somehow deeper into a face hardened or homogenious plate and materially reduce the stress on the projectile nose from the plate's no-longer-solid face layer during the later stages of the penetration process of KC armor. Against homogenious armor the pure impact effects are less significant as long as RHA acts in ductile failure mode (some plastic displacement of armor).
Other than that the cap is gone after impact and the projectile itselfe has to do perform the penetration.
The latter point is important because it means that the thicker the cap, the more deadweight has to be carried by the projectile into the target. Thus, the smallest cap, which manages to prevent any projectile nose breakage or projectile shatter will be the best.

At high obliquity, the cap aids a bit in righting up the projectile towards the perpendicular but for this the cap is eroded away, it needs a very strong, high temperature solder or otherwise solid attachment to the projectile nose and it needs a deeper thickness to work.

At extreme obliquity and against thin, ductile plating, You want to have a blunt projectile tip and the cap can offer sharp edges and blunt tips by covering the pointy projectile nose. This will help reducing projectile ricochet effects.

The Navy type, sombrero shaped AP-cap with a central bulge allows both, sufficient depth in front of the nose and sharp edges along it´s circumference. The concave conture lines reduce the amount of weight "wasted" in the cap. The design is therefore geometrically more "efficient"* than the heavier, Army type "deep" cap.

However, it is also less "effective"* than the Army type cap because projectile break up can occur at somehow lower velocities. That may have been a probelm for the 88mm Pzgr39/43, which had the Navy type cap but which would frequently suffer break up against plates thicker than 180-200mm (which the projectile could defeat at low range and low obliquity). For the ultra high velocity 12.8cm/8.8cm Pzgr39TS the 88mm core was to be fitted with the Army type cap in order to negotiate higher impact velocities.

The loss of penetration caused by a cap is proportional to the weight used up in the cap. That´s why some ww1 Navy APC projectiles had very light caps attached. However, as You may have noticed, the requirements for an efficient penetrator and an intact penetrator are in conflict with each other and the harder the armor attack (e.g. higher obliquity attack, harder tensile strength, higher cal/plate ratio), the higher the projectile stresses. Projectile break up caused by these higher stress exposures may disproportionally reduce penetration, depending on the grade of break up and that´s why there was a tendency to employ deeper, heavier and harder caps.

I suppose the 88mm Pzgr39 and 105mm Pzgr 39 rot kept the Navy type cap because there was no threat in form of a very thickly armored AFV target which needed to be engaged at high enough velocity to cross the velocity/stress treshold for projectile break up (IS-3 and TORTOISE qualify here but arrived only post ww2). Because these targets were lacking, a thinner Navy type cap was the more efficient choice for t-h-e-s-e projectiles at all other conditions, including at long range vs moderately thick, sloped armor.

*) I suppose the difference between efficiency and effectivity is commonly known

[EPOCH3]

Hi - just wanted to say that I have read this thread from afar from time to time and while it's above my pay grade, its a very interesting discussion and I have learned a lot from you all sharing your knowledge on the topic. Please find attached a few pieces of art. These are photos of large learning posters that were hung on the walls of one of the APG buildings during the war and came from a small archives of material that had once belonged to Charles Yust.
Kind Regards

[critical mass]

Interesting.
The table show the training projectile and a Pzgr40W projectile.
This was the only APBC projectile employed by the german Army. It did not had an explosive filler but could be fitted with tracer.
The body was of short length and soft iron (hence W-weich), covered by a thin, ballistic windscreen. It was flat nosed.

This projectile was introduced in repsonse to soviet thin, highly sloped and high hardness armor on the easstern front. The projectile deforms on impact, much like soviet blunt nosed APBC projectiles do, and works by pure shear effects driving out a plug of armor perpendicular to the plate negating any slope. This is important, the slope has little effect on these projectiles, quite unlike the rigid, Pzgr40(hk) penetrating projectiles. The Pzgr40(w) was kind of a poor men´s AP variant of what later became the HESH principle but relying on kinetic rather than chemical energy. Due to the projectile deformation, it has more impact area than a normal projectile would, thus, be not suited to perforate thicker plates than other, rigid penetrators. For it´s target effect it has to rely on the armor plate itselfe. However, while it doesn´t carry any explosive charge (hence the Pzgr40 designation), it can induce the plate to shatter or to plug. Like in a billiard effect, where the white ball hits another ball and is stopped cold, while the other ball takes the energy of the former. For this effect to be present, the projectile needs to remain in one piece to transfer much of it´s kinetic energy into the plate. Thus, deformation was allowed but not breakage and this demanded a very ductile, soft material. However, deformation also rendered any explosive cavity useless. As with all shear phenomena (f.e. face hardned armor plugging failure), velocity has a considerably higher power than weight. Thus a lower weight is acceptable if the velocity is larger, which is exactly what we see in the Pzgr40W. High hardness armor has good resistence to tensile forces but inferior shear strength. Due to the lower shear strength of high hardness materials, this projectile is also more capable against HHA than other, ductile forms of softer RHA. Typically, such projectiles were considered not very effective against much more than 2/3 cal (german) RHA plate. The higher the hardness of the target plate the thicker the effective cal/ plate ratio.
Consequently, the Pzrg40W would be effective against highly sloped, thin HHA target plates, such as 45mm T34 glacis plate or thin, sloped AFV armor (T60/70/80) but it will be very ineffective vs. for example, ductile, soft Sherman front armor.
Unlike later HESH, which was effective to 1.20 cal/ratio at high obliquities, the Pzgr40W APBC(APSH) is only effective at 2/3 to 3/4 cal/plate ratio´s, depending on target hardness.

[Yoozername]

These rounds were used in the 'Yugo Tests'. See Pak 40 page...

http://www.panzer-war.com/

Apparently not penetrating the T34/85 glacis, but perhaps there were after armor effects. Interesting that they did penetrate the Sherman.

[Mobius]

Per the Yugo tests to say that the Pzgr. 40w was effective against any armor is optimistic.

[critical mass]

Outright penetration wouldnt be expected from-40W.
There might even be no holing event. Inside armour scabbing is its task, and I am sceptical that this effect was properly factored in by the Yugo tests.
Note that the penetration against the soft but very thick (90+mm) Sherman turret armor is a good indicator for the presence of temper brittleness in this rather soft Casting. The 50mm M39 failed to penetrate but the 75mm 40W, which induces more shear stress than the M39, managed to penetrate.

[Yoozername]

deleted....wrong thread

[Sheldrake]

Does anyone have the firing table data for this equipment firing HE in the terms that I understand as a field gunner. i.e.

a Range at a given elevation?
b. Probable error of range at a given range?
c. Variation of range with variations in MV?

[Michael Kenny]

I don't quite agree with the conclusion....................................

It is a translation of a German Document dated August 1st 1944.

The link connection to where the quote came from seems to be missing a lot in this thread (the small arrow pointing 'up' right after the name of who you quoted that links you direct to the post)) and I can not find the original poster..

[Yoozername]

I don't quite agree with the conclusion....................................

It is a translation of a German Document dated August 1st 1944.

The link connection to where the quote came from seems to be missing a lot in this thread (the small arrow pointing 'up' right after the name of who you quoted that links you direct to the post)) and I can not find the original poster..

It was actually meant for another thread. So I deleted it. Not sure what you are saying otherwise. Please, no need to expound on it. I am sure that not just I was warned about 'dullery'....?

[Michael Kenny]

It was actually meant for another thread. So I deleted it. Not sure what you are saying otherwise.

It was a pretty stilted translation. The version on page 205-206 of Muller & Zimmermann's Sturmgeschutz III V.1 flows much better and, if I knew the context of the original poster's reply, I could see if this made any difference to how it comes across.
Was it from a Norbert Szamveber book?

[Mobius]

Outright penetration wouldnt be expected from-40W.
There might even be no holing event. Inside armour scabbing is its task, and I am sceptical that this effect was properly factored in by the Yugo tests.

The Yugo penetration criteria was the same as the US criteria at the time. 50+% of the mass passing through the armor 50% of the time. How the Germans measured the armor penetration of the projectile given their criteria methodology would be interesting.