German service acceptance conditions for AP ammunition in ww2

[critical mass]

It has often been articulated, partly because of british and US opinions expressed post VE day, that the germans stabilized their ideas about AP mass production already before outbreak of ww2 and changed little during the conflict. Access to primary sources indicates that contrary to this assumption, great effort was spent to improve the quality of mass produced armor piercing ammunition, partially due to differing manufacturing techniques, involving different steel mixes and the switch to heats created exclusively by the Siemens Martin Electro Duplex- or the Thomass Electro Duplex-process and partly due to more care taken in heat treatments. The following tabulations list together the official service acceptance requirements, which all mass produced AP ammunition had to pass in order to be declared servicable. A significant change in severity of acceptance conditions took place 1942, coinciding with the widespread advent of Pzgr 39 series AP ammunition. The increased severity is reflected by the generally higher impact velocities, which the AP projectile had to negotiate staying intact, rather than to break up in penetration. Thus, higher velocities are a more challanging test doe the quality of the projectile.

It doesn´t need to be explained that the tests were made to ensure a minimum penetration performance under service conditions not too far off the officially rated performance. The composite 75mm Pzgr39 was even tested exactly on the officially rated performance, which by the standarts of 1942, must have been considered an example of exceptionally tight quality controll, resulting in most of the 75mm Pzgr 39 projectiles encountered in mass production having a performance in excess of their officially rated paper performance.

Original german service acceptance requirements for mass produced, service AP ammunition (PzGr.).

Projectiles from EVERY heat were selected for ballistic and physical tests. WaPrüf would select randomly from a lot or based upon suspicious quality after examination of the presented lot at the manufacturer, they would select six projectiles for tests from each lot. One lot beeing typically one heat. If for some reason more than one heat was combined for a single projectile lot, then WaPrüf would select a proportionally larger number of test specimen to ensure quality.

disclaimer: german obliquity figures are defined with 90° = perpendicular. In order not to mix it up with other services, I have transformed all german original data into the more common standart 0° = perpendicular instead.
Source: BAMA RH 8-1319 (primary source)

up to 1942

5cm monobloc Pzgr Gg.
Plate thickness: 45mm RHA
tensile strength: 120kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 540m/s

2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)
Notice: Officially rated performance was 50mm RHA at 30° and 540m/s for the Pzgr Gg.

7,5cm composite Pzgr39
Plate thickness: 100mm RHA
tensile strength: 100kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 750m/s

2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 100mm RHA at 30° and 750m/s for the Pzgr39 (!).

7,62cm monobloc Pzgr39 rot
Plate thickness: 60mm RHA
tensile strength: 120kg/mm² +- 5kg/mm²
velocity: 620m/s

2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

8,8cm monobloc Pzgr Gg
Plate thickness: 55mm RHA
tensile strength: 110kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 600m/s

2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 72mm RHA at 30° and 600m/s for the Pzgr Gg. Attempts to raise the acceptance conditions to 75mm Pzgr39 levels failed because while the 100mm plate could be holed reliably at 750m/s by the 8.8cm Pzgr, the damage to the lower projectile body rendered the AP blind.


1942 to 1944


5cm composite Pzgr39
Plate thickness: 55mm RHA
tensile strength: 110kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 740m/s

demands on the projectile:
impact toughness at base: lengthwise: >8 mkg/mm² but no less than 6 mkg/mm², perpendicular: no less than 4mkg/mm²
Rc hardness: Rc60 at nose (outside and centre), less than Rc57 and the lot will not be passed to ballistic test and directly rejected.
2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 62mm RHA @ 30° and 740m/s for 5cm Pzgr 39.

7,5cm composite Pzgr39 and monobloc Pzgr 39/42
Plate thickness: 100mm RHA
tensile strength: 100kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 750m/s

demands on the projectile:
impact toughness at base: lengthwise: >8 mkg/mm² but no less than 6 mkg/mm², perpendicular: no less than 4mkg/mm²
Rc hardness: ideal: Rc61-62.5 at nose (outside) and Rc 60-61 (centre, no less than Rc59), less than RC 56 anywhere at nose and the lot will not be passed to ballistic test.
2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 100mm RHA at 30° and 750m/s for the Pzgr39 (!).

7,62cm monobloc Pzgr39 rot
Plate thickness: 80mm RHA (1944 amended to 100mm RHA)
tensile strength: 110kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 650m/s (1944 amended to 740m/s)

demands on the projectile:
impact toughness at base: lengthwise: >8 mkg/mm² but no less than 6 mkg/mm², perpendicular: no less than 4mkg/mm²
Rc hardness: ideal: Rc60-61.5 at nose (outside) and RC 60 (centre, no less than Rc59), less than RC56 anywhere at nose and lot will not be passed to ballistic test.
2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 85mm RHA at 30° and 650m/s for the Pzgr39 rot.

8,8cm monobloc Pzgr 39-I
Plate thickness: 140mm RHA
tensile strength: 90kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 830m/s

demands on the projectile:
impact toughness at base: lengthwise: >8 mkg/mm² but no less than 6 mkg/mm², perpendicular: no less than 4mkg/mm²
Rc hardness: ideal Rc59 at nose (outside and Rc56 in centre), less than RC55 encountered anywhere at nose and lot will not be passed to ballistic test.
2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 140mm RHA at 30° and 825m/s for the Pzgr39 & Pzgr 39/43.

8,8cm monobloc Pzgr 39/43
Plate thickness: 160mm RHA (1944 amended to 180mm RHA)
tensile strength: 90kg/mm² +- 5kg/mm² (1944 amended to 80-90kg/mm²)
obliquity: 30°
velocity: 900m/s (1944 amended to 950m/s)

demands on the projectile:
impact toughness at base: lengthwise: >8 mkg/mm² but no less than 6 mkg/mm², perpendicular: no less than 4mkg/mm²
Rc hardness: ideal Rc59 at nose (outside and Rc56 in centre), less than RC55 encountered anywhere at nose and lot will not be passed to ballistic test.
2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 165mm RHA at 30° and 900m/s and 180mm RHA at 940m/s for the Pzgr 39/43.

10cm monobloc Pzgr rot
Plate thickness: 100mm RHA
tensile strength: 100kg/mm² +- 5kg/mm²
obliquity: 30°
velocity: 650m/s

demands on the projectile:
impact toughness at base: lengthwise: >8 mkg/mm² but no less than 6 mkg/mm², perpendicular: no less than 4mkg/mm²
Rc hardness: Rc59 at nose (outside and Rc55 in centre), less than Rc54 encountered anywhere at nose and the lot will not be passed to ballistic test.
2 shots. If both penetrate intact, lot passes(A). If one fails, another projectile from the lot is retested and lot only passed if that projectile penetrates intact(b). Else, lot is rejected.
= (A) 2 out of 2 or (B) 2 out of 3 successes in intact bursting condition (projectile damage does not reach cavity or fuze adaptor)

Notice: Officially rated performance was 115mm RHA at 30° and 650m/s for the Pzgr rot. Attempts to raise the acceptance conditions to 160mm @ 800m/s failed because the projectile was not always remaining intact.

[Yoozername]

How big was a lot typically? Were the shoots done at the actual manufacturing facility?

[critical mass]

The size of the lot varies from manufacturer to manufacturer because it depends on (A) the main ingot size from the heat and (B) the size of the projectiles to be manufactured from this heat. Remember, in order to guarantee homogenity, specimen of every heat had to be tested before passing to service. However, the furnaces differed between the manufacturers, and sometimes even within the company if more than one specific furnace design was used. Different furnaces had different ingot sizes and not everything could be used from each heat.
For 7.5cm Pzgr39 and the Bochumer Verein, f.e. the usual lot size ranged between 800 and 1000 AP projectiles per lot during 1943, lots for 7.62cm Pzgr39 rot were only slightly smaller. While the lot size of the largest projectiles manufactured by Bochumer Verein, the 1t heavy 40.6cm L/4.4 naval APCBC was considerably smaller. The ingot size of ~40t provided only for 21 to 23 raw projectiles from each heat going into a lot.
Out of those, two were used up to determine the best heat treatment for hardening, two were used for physical testing and determination of correct hardness and toughness and 2-3 were used up for the ballistic tests.

The projectiles were not selected by the company but by WaPrüf ordnance inspectors. They customarely selected the most dubious ones for testing after visual examination of the presented lot. Ballistic tests were conducted at the Army prooving grounds (Hillersleben) for tank/ anti tank ammunition.

[Yoozername]

This is great info for English speakers. It is an insight into data and concepts (specifications/QC) that really bring light to previous discussions and assumptions. There are things that make me want to discuss further, but I just want to thank you for these posts first. I enjoy your efforts heer.

[critical mass]

Glad to be of help.

Attached are the projectile drawings and hardness contour data for the AP projectile referred to in my previous memo.
These represent the standart service projectiles issued to tank and anti tank units from 1942 to ca. 1944 (not experimental).
The change of acceptance specification issued 1942 was directed primarely towards the obliquity of proof, which was changed from 30° to 45° with an associated drop in thickness of plate to be penetrated intact.

As can be seen, the size of the filler was significantly altered from pre1942 to post 1942, particularely in 7.62cm and 8.8cm projectiles. The same happened slightly earlier for the 7.5cm projectiles.
The reduction in size of the cavity was deemed necessary in order to provide for the requirement to stay intact post penetration. Only such a requirement could allow for an delayed burst (that is bursting after penetrating), or fragmentation ("Zerlegung") as intended -also against thick armor plate- in order to get most effect out of the lethality of the projectiles.

Notice that only if the cavity stays intact during penetration that the HE filler will have a high order effect. If the cavity is cracked open, the HE filler does merely burn or blow out/ conflagrate with typically only 1/3 as violent explosions. For the small cavity Pzgr39 series APCBC-HE, if the cavity cracked open, then the filler will not be powerful enough to completely fragmentate the body due to the small size. Unfortunately, the ideal steel for protection of the cavity is tough/ductile and not hard/brittle and thus stands in conflict with the requirementfor hard steel in the projectile nose for ideal penetration.
Homogene steel bodies also don´t like dissimilarities in hardness because they form triaxial stress zones in impact which may create conditions for breakage or deformation. The decremental hardening was thus not linearely dropping but plateauing off in the nose for maximum robustness and then slowly starting to drop in a ski slope shape and plateauing off again at the base. This hardening treatment gave the best compromise between the conflicting demands on the projectile.

Particularely for some late ww2, large calibre APCBC-HE projectiles of the 10.5cm and 12.8cm Pzgr43 series (not shown here), it was considered possible to keep a large cavity when the hardness contour was changed towards a more sophisticated sheath hardening (hard outer surface down to below the forward bourrolet and softer core around the driving bands and the cavity, even in the nose), as was practices in naval AP ammunition since some time. For smaller projectiles, experiments with sheath hardening were not successful.

[critical mass]

Attached is a graph showing the chart of chemical reference composition for SGW, a manufacturer for 7.5cm, 7.62cm and 8.8cm Pzgr projectiles.

As can be deduced from the graph, there are three general periods. All development was intended to improve performance and reduce the amount of critical alloys necessary to make a high performance AP.

initial period.
The period until 1940 saw the utilization of relatively alloy rich shell steel. A further development of Krupp Ni-Cr steel (typically Nickel and Chromium in the relationship two to one), in which Molybdenium was added in small amounts for better controll of the tempeing temperature ranges (to avoid temper britellness). Nickel beeing the principal toughnening and Chromium the principal hardening agent. The amount of Carbon was moderate.

Until 1941/2.
This period saw a rapid decline of some important and expansive alloys in the shell steel. The amount of Nickel present in the shell steel was first reduced and then omitted entirely. The even harder to obtain Molybdenium beeing gradually replaced by Vanadium, which was easily accessible. The amount of Chromium was increased in order to obtain greater through hardness. AP of these series with Chromium-Molybdenium - or Chromium-Vanadium alloys were of relatively lean alloy composition compared to older shell steel and in monobloc types had troubles to stay intact in mass production due to a lack of toughness owing to the omission of Nickel. A welded on tip with richer alloy composition was used to correct the troubles by allowing the shaft to be heat treated soft and ductile with only the nose hardened through. The amount of Carbon was keptmoderate due to the need to weld the tip on the shell body.

From 1942 to wars end.
This period is characterized by a gradual adoption of new shell steel. The amount of Chromium present in the shell steel was reduced from 2.0% down to 0.4% while at the same time both, Manganese and Silicium were increased substantially and became the principal toughening agents working together with residual Chromium and the Carbon to obtain toughness and through-hardness. Vanadium acting as anti-embrittlement agent to controll heat treatment rates. This Silicon-Manganese, low Chromium shell steel had a high carbon content, which was made possible by re-adoption of monobloc shells and thus, by dropping the requirement of welding. Tempering temperatures and careful controll of the entire heat treatment were critical in obtaining high quality projectiles despite the very lean alloy composition.

Soviet late and post ww2 shell steels used for 76mm and 85mm were not too dissimilar -chemically- to mid war (ca. 1942-1944) german shell steel. However, there are significant differences, too. Apart from the preference of more homogenious, cleaner electrosteel and Duplex process for the shell steel heats in Germany, the quality controll ceiling for embrittling Sulphur and Phosphorous inclusions was higher in soviet shell steel and unlike the german heats, they had very much less carbon (and consequently, a lower through-hardenability) and used more residues of Nickel and Molybdenium. Compared to later, chromium-poor ww2 Pzgr39, soviet shell steel generally were of richer alloy compositions, and often included Nickel, Chromium or Molybdenium in ample amounts, particularely in 122mm calibre which relied on the original Krupp steel mix instead of the Silico-manganse sorts:

76mm BR-350B: C:0.34%, Mn: 0.84%, Si:1.54%, Ni: 0.25%, Cr: 1.30%, Mo:0.06% [3.99% alloy + C]
85mm BR-365B: C:0.32%, Mn: 0.92%, Si:1.41%, Ni: 0.22%, Cr: 1.17%, Mo:0.03% [3.75% alloy + C]
122mm BR-471: C:0.35%, Mn: 0.36%, Si:0.29%, Ni: 1.19%, Cr: 2.35%, Mo:0.22% [4.41% alloy + C]

Despite beeing of a notoriously lean alloy composition [=2.2% alloy+C to 2.5% alloy + C], and free of critical Nickel or Molybdenium, the more careful heat treatment of the later, chromium-poor shell steels guaranteed the Pzgr 39 series a performance significantly superior to shell steels encountered in other countries, or even the older, more alloy rich, german shell steels used pre war or up to 1942 domestically. The difference is economically important when ressource limitations are imposed upon. A remarkable metallurgic achievement.
For 1000 Pzgr39 mod. 1944 shells, the only critical ressource needed are about 50kg of Chromium (Vanadium could be readily extracted from Bessemer slag, while carbon, Manganese and Silicium are not short in supply).
Similarely, for 1000 Br-471 shells, You would need about 600kg of chromium, in addition to 300kg of nickel and 55kg of Molybdenium. The amount of Chromium required here alone would be sufficient for production of approx. 12,000 Pzgr39 mod. 1944 shells instead.

[Yoozername]

Excellent, it is like you are a metallurgical detective. Did the Germans deliberately use 'good scrap' so as to recover some alloys for AP rounds?

[critical mass]

Yes they did on a regular base to obtain shell steel. They would add 17t of alloyed scrap metal to a typically sized heat + 0.3t fresh iron ore + 0.2t chalk. They would generally add desoxydation and dehydration agents to the heat, but recover all critical alloys from the alloy present in the scrap.

Critical to the success was the careful controll of carbon and manganese content of the heat. Manganese should not be allowed to raise >0.8% because a relatively high carbon (0.5%-0.59%) was required (only for large projectiles, and only when the chromium and silicium content was lowered, too, could a higher manganese ~1% be tolerated). A high managense correlated with reduced impact toughness and the latter correlated with a higher %age of base breakage when attacking obliquily (=projectile breaks up at lower stress levels).

[Peasant]

I've noticed that the germans seems to go about the development of their tank/AT guns the following way:

1. They determine the thickness of armour required to offer complete protection from the current mass produced system for a vertical plate at 100m.
2. They then compile specifications for it's successor that will have to be able to defeat this thickness of armour at 30° angle at far out as possible.

For the 3.7cm PzGr. the thickness required to offer complete protection is 50mm, the acceptance tests for the 5cm PzGr.39 is the same thickness at 30° and it can perforate it at up to 900-1000m. 160mm of vertical armour is required to offer complete protection from 7.5cm Pak 40 fired at 790m/s, the same thickness required for the 8.8cm shell from the Kwk 43 to defeat at 1000m.

[Timber]

Hello Critcal Mass,

You've mentioned that the acceptance standards changes some time in mid 1944, to occur at 60 instead of 30 deg. Are there sources on this?

[ThatZenoGuy]

Hello Critcal Mass,

You've mentioned that the acceptance standards changes some time in mid 1944, to occur at 60 instead of 30 deg. Are there sources on this?

I've heard the standards were changed from 30 to 45, not 60. ;V

[Thoddy]

According E. WAGENKNECHT Chief quality management the 8,8 cm Psgr from Bochumer Verein reached in 1944 a maximum performance of this projectile against 305 mm homogenous armour plate at 1280 m/s at 30 degrees obliquity(60 degrees Auftreffwinkel). Projectiles were randomly choosen from ongoing production.

as a result the condition for acceptance shelling was increased to 180 mm at 45 degrees from 140 mm.

They used 150 mm guns with a 88 mm sabot.

[Denniss]

60 degress from horizontal or vertical ? Always a source of confusion

[ThatZenoGuy]

60 degress from horizontal or vertical ? Always a source of confusion

I think 60 from horizontal like most German tests?

[Thoddy]

Perpendicular to plate
Auftreffwinkel 90°= obliquity 0°