7,5cm 40 caliber /43, /46 & /48 penetration power

[PreußensGlanz]

Hi
I was going thru different sources to compare the penetration power of the different caliber versions but I don't get a consistent result, for example some sources show more penetration power(using same ammo, range & angel of impact) for the /46 than for the /48 but some also less.

My basic question is if the caliber alone can determine the penetration power if same ammo, range, angel of impact, etc. is used or could there still be differences in the gun that have impact on the penetration power?

[peeved]

In the case of 7,5 cm Pak 40 vs KwK 40 (L/48) when comparing penetration figures from several sources a major difference may be due to variations in target steel quality, especially hardness. Another source of differences is typos in period etc. documents: E.g. my reprint of a 1944 Datenblätter für Heeres-Waffen, -Fahrzeuge, -Gerät has KwK 40 (L/43) v0 and penetration data repeated for (L/48) etc.

Markus

[EugE]

As I understand the /43 & /48 it's tank cannons, is the /46 - Pak-40 ?

[PreußensGlanz]

Yes 43 & 48 are for tanks & assault guns and 46 is the Pak version.

Target Steel Quality is a good point but I also see different muzzle velocities ranging from high 7xx(up to 790) down to mid 7xx(like 740) for the Pz.Gr.39.
Did the quality and with it also the performance change over the course of the war or what can be the explanation?

[peeved]

I've seen ca. 790 m/s v0 figures for Pak 40 from Western Ally sources. Since they to my knowledge first captured Pak 40s in the North African theatre of war it is possible that the high v0 and penetration figures are from tests made in Africa. High ambient temperatures can e.g. increase chamber pressure and elevate the pressure curve as a whole and thus have an effect on muzzle velocity; Tests made in Africa could quite reasonably show higher v0s than tests in Germany. A typo could also quite easily have produced some of the high end v0 figures.

English units are also a potential source of confusion since the penetration figures will usually not be from the same range as German tests but e.g. 0, 500, 1000, 1500 & 2000 yards. Simple misquotation would turn yards into metres and produce faulty data with exaggerated penetration.

Markus

[Christian Ankerstjerne]

I've tried gathering some information from three different sources, which originate from German war-time documents:

Code: Select all

                       MV         100 m   1000 m
7,5 cm Kw K 40 (L/43)
  Pzgr. 39
    Datenblätter       750 m/s     99 mm   82 mm
    Panzer Truppen 1   740 m/s     99 mm   81 mm
    Panzer Truppen 2   740 m/s     99 mm   81 mm
  Pzgr. 40
    Datenblätter       920 m/s    125 mm   88 mm
    Panzer Truppen 1   990 m/s    126 mm   87 mm
    Panzer Truppen 2   920 m/s    126 mm   87 mm
7,5 cm Pak 40 (L/46)
  Pzgr. 39
    Datenblätter       750 m/s     98 mm   82 mm
  Pzgr. 40
    Datenblätter       930 m/s    126 mm   67 mm
7,5 cm Kw K 40 (L/48)
  Pzgr. 39
    Datenblätter       750 m/s     99 mm   82 mm
    Panzer Truppen 2   740 m/s     99 mm   81 mm
    New Vanguard 39    750 m/s    103 mm   85 mm
  Pzgr. 40
    Datenblätter       920 m/s    125 mm   88 mm
    Panzer Truppen 2   920 m/s    126 mm   87 mm
    New Vanguard 39    930 m/s    143 mm   97 mm

Aside from the 67 mm penetration at 1000 m for the 7,5 cm Pak 40, as noted in Datenblätter, these numbers do seem to make sense. The 67 mm are most likely a clerical error. The Datenblätter are hand-written, and an unclear 8 could easily mis-interpreted as a 6.

The main source of confusion is most likely that the L/43 and L/48 guns are grouped Datenblätter and Panzer Truppen 2. New Vanguard explicitly names the L/48, and Panzer Truppen 1 only mentions L/43. Let us assume that the grouping was done by the Germans, not because of identical test results, but because they only tested one of the guns, and used the result on both. This could give us the following table:

Code: Select all

                       MV         100 m   1000 m
7,5 cm Kw K 40 (L/43)
  Pzgr. 39             740 m/s     99 mm   81 mm
  Pzgr. 40             920 m/s    125 mm   88 mm
7,5 cm Pak 40 (L/46)
  Pzgr. 39             750 m/s     98 mm   82 mm
  Pzgr. 40             930 m/s    126 mm   87 mm
7,5 cm Kw K 40 (L/48)
  Pzgr. 39             750 m/s    103 mm   85 mm
  Pzgr. 40             930 m/s    143 mm   97 mm

This would match the highest muzzle velocities (and, largely, the best penetration results) to the longest barrels. The only exception is the one mm discreprency of the Pzgr. 40 for the L/43 and L/46, which is a perfectly reasonable discreprency for real-life firing tests.

Note that this is all speculation, but the numbers do make sense to me.

[peeved]

Aside from the 67 mm penetration at 1000 m for the 7,5 cm Pak 40, as noted in Datenblätter, these numbers do seem to make sense. The 67 mm are most likely a clerical error. The Datenblätter are hand-written, and an unclear 8 could easily mis-interpreted as a 6.

That does seem to be the cause for the 67 mm figure. E.g. according to Waffen und Geheimwaffen des Deutsche Heeres 1933-1945 by Fritz Hahn Pak 40's Pzgr. 40 penetration at 1000 m was 87 mm (plate at 60 deg from horizontal as usual in German stats).

Markus

[peeved]

Comparing Hahn and Datenblätter numbers appears to confirm another clerical error in Datenblätter: Repetition of L/43 data for L/48.

Included Allied Pak 40 data from German Tank and Antitank by Hoffschmidt and Tantum at different angles of attack (converted to European convention and units). Since the elevated Pzgr. 39 v0 figure is reflected in good penetration figures the Pzgr. 39 test appears to have involved an unusually hot batch of ammo. Note erroneous Pzgr. 40 weight in the Allied data.

Markus

[Christian Ankerstjerne]

It's difficult to compare different countries' test results, as different countries had different standards for penetration.

Another point, which is quite significant, is that the charge of the Pak 40 ammunition was significantly larger than that of the Kw K 40: 2750 g vs 2430 g for the Pzgr. Patr. 39, and 2700 g cs 2180 g for the Pzgr. Patr. 40.

[peeved]

It's difficult to compare different countries' test results, as different countries had different standards for penetration.

That certainly is true. However it is interesting to note that for the Pak 40's Pzgr. 40 penetration, where the v0 was more or less constant in both German and Western Allied tests, the charts give rather consistent results.

Another point, which is quite significant, is that the charge of the Pak 40 ammunition was significantly larger than that of the Kw K 40: 2750 g vs 2430 g for the Pzgr. Patr. 39, and 2700 g cs 2180 g for the Pzgr. Patr. 40.

On the other end of the scale the rifling length of Pak 40 was slightly less than the KwK 40 L/43 and considerably less than L/48 which together with the fact that short but fat bottleneck cartridges tend to be more effective ballistically than long and slender ones might suggest that the KwKs were getting more bang for the buck.

Markus

[Yoozername]

The KWK 40 L43 and Pak 40 had the same length of rifling.

From Miles OP thread...

viewtopic.php?f=47&t=221644&start=60



As I say in that thread, there can be no way that the L43 and the Pak 40 had the same velocity. If they have the same barrel rifled length (2470.5 mm), and the Pak 40 had more powder (it did), then the velocities would not be the same. Every bit of evidence is that the Pak 40 had 2.69-2.75 Kg of propellant powder. The only known lower charge was a Fur Tropen round.

The KWK 40 weapon probably got the larger powder charge of 2.5 Kg (up from 2.43 Kg) around the time of Kursk when Panzer IVs with the L48 became more common. The Panzer IV actually had L43 for a longer production time than the StuGs. Clearly, the StuK mountings allowed more recoil distance. Also, the muzzle brakes went through some iterations which may have delayed L48 panzer IV weapons.

In any case, there would be more penetration with higher velocity. The KWK 40s would have a higher velocity with the later 2.5 Kg ammunition.

The Pak 40 was initially 2.75 Kg and this is said to be reduced to 2.69 Kg and there is a document that states 2.71 Kg and also a powder silk bag that shows 2.73 Kg (see thread link). In any case, there was no reduction of the Pak 40 to 750 M/s, if it was, then it would have a 2.5 Kg charge which it never did...even in a Fur Tropen round! It would be in the 770 M/s t 792 M/s range.

[critical mass]

Attached the penetration (G_D) of the 75mm with Pzgr39 at various obliquities for different muzzle velocities. Tests performed 1943 using ammunition "in production". Penetration definition is 5 out of five successes in a row (no failure tolerated), the plate strength is shown, too.
From the Lilienthalreport 166 (originally classified SECRET), 1943.

[Yoozername]

The Germans were a bit off when it came to attacking highly sloped armor. Armor at 30 degrees, like the T34 front hull, would be very difficult to get '5 out of 5'. In reality, a specification like 4 out of 5 would have been more realistic. I believe they tested extensively with 60 deg primarily and only later in the war at 45 degree. Given the threat from t34, even that was not realistic.

If we look at that chart, the 30 degree line might be extended back linearly and 750 M/s is the velocity for penetrating the 110-125 Kg/mm armor of 45mm. But weapons like the Pak 40 and KWK 40 could penetrate or get lethal results on the T34 front at greater ranges than nearly point blank.

The 60 degree line shows a non-linear response as it is tested over decreasingly hard armor. It is showing a phenomenal performance considering the velocities.

[critical mass]

True, 5/5 is quite difficult to obtain consistently, particularely under the more variable conditions of projectile break up. However, note that the G(D) curves for 45° and 30° in the graph above are worst case (i.e. projectile break up). Thee projectiles were much better if they stayed intact.

For whats worth, Prooving ground Report #35472, deals with the firings at Aberdeen on 6th of february and 7th of february using 75mm Pzrg39 fired by KwK42 tank gun.

Target plate was 5" nominally thick (127mm, actually between 130.2 and 131.8mm thick when meaured) at BHN 217-230 levels made by Carnegie-Illinois (plate ID TT-281 1/4). Tests were conducted at 30° (60° in german definition) and 45° impact.

Note that the G(D) curves for this projectile provide the following penetrations by german standarts:

835m/s: 120mm RHA @60°
950m/s: 94mm RHA @45°

Against the actually 5 3/16" US RHA plate (131.8mm), which greatly overmatched the attacking projectile (ca. 1.75 plate/cal ratio) the following limits were obtained at the prooving ground:

at 44°30´: Army & Navy BL 3127fps (953m/s)
at 29°30´: Army BL: 2543fps (775m/s) and Navy BL: 2733fps (833m/s)

The excellent performance against US RHA at 45° was, of course, possible because the 75mm Pzgr39 stayed intact, whether or not it rebound or penetrated. The US armor behaved ductile, as could be expected from such soft material. The good obliquity performance was probably also effected by some measure of normalization, aided by the blunt nose shape and relatively thick AP-cap, the exit hole in the plate was clean and circular 3" x 3".
German prooving ground data actually emphasizes that for highly oblique impact, the AP-cap needs to be thicker, or problems with penetration performance will occurr. Krupp even tested specimen where the cap was sheathed once around the projectile covering even the base -with excellent results at extremely oblique 30° and 15°).

There occurs quite often the misconception that an APBC is better for highly oblique impact than an APC or APCBC projectile. These ideas are valid only in a very narrow frame of conditions, and frequently, these conditions are misunderstood.
Because the cap is carried by the projectile as deadweight, not adding to the penetration process a lot per se (except for the initial contact, or against very thin plating, which doesn´t strip off, deform, or knock off the cap), plain solid AP will be better than APC under conditions where both projectiles stay intact, which requires fairly low impact velocities (speak: long range) or exceptionally soft target materials.
Generally, the cap allows an APC to negotiate much higher impact velocities and much harder target materials intactly than an AP could ever hope to (the reason why the Navies were the first to adopt capped AP in order to find something against their projectile shatter problems caused by the then newly introduced KC face hardened armors).
F.e. the uncapped 5cm Pzgr Gg starts to experience break up at 60°(germ. def.) at 560m/s while the capped 5cm Pzgr39 will stay intact at over 900m/s. Therefore, the uncapped 5cm Pzgr Gg has the advantage below ca. 600m/s and the capped Pzgr 39 above ca. 600m/s. Because the germans preferred high velocity tank guns, there was no way around the capped AP.

Softer projectiles, such as soviet AP and APBC will likely experience these issues at even further reduced velocities with the added negative side effect of exhibiting more projectile deformation, such as bending (offset and compression) failures. Break up can- at times- help in oblique penetration but bending never helps.With break up, different penetration mechanics replace those for ductile hole formation.

The addition of a ballistic cap is always detremental to oblique impact performance, particularely, when no flat maplet is added. In Navy APCBC, they tried to negate the effect by using a thin, siluminium, break away type of ballistic cap. After all, the effect is very small, but not negliable, particularely when steel windscreens are used.