German 7,5cm gun question

[Mattias]

What exactly are the differences between the German 75 mm guns in the L/46-L/48 range?

I can see that...

The PaK40 is the gun used as standard AT gun by the Germans, it was also mounted on many of the open topped Panzerjäger SPG's.

This gun used ammunition with a long slender cartridge case, the Pzgr.Patr.39 measuring 969 mm in total.

In CM this guns is rated at 792 m/s with a penetration of 108 and 100 mm @ 100 and 500 meters respectively (30 degrees).

In order to fit a weapon of similar capacity into the Pz IV tank turret the KwK40 was designed. It has a more compact breech, substantially shorter recoil and fires ammunition with a shorter and thicker cartridge case, the Pzgr.Patr.39 measuring 748 mm.

In CM this guns is rated at 750 m/s with a penetration of 101 and 93 mm @ 100 and 500 meters respectively (30 degrees).

So far so good, but what about..

The PaK39 mounter in the Hetzer and PzJg IV? CM portrays it has having identical performance to that of the PaK40, yet it fired the same ammunition as the above mentioned KwK40 and the, soon to follow below, StuK40 and had, as far as I have seen, the same basic dimensions. So, how come the difference in performance?

And the same goes for the StuK40 mounted in the StuG III and IV's. It too fired the stubby ammunition (no doubt a good thing in those notoriously cramped enclosed SPG's). On paper it looks like the same gun as the KwK but, as with the PaK39, with a different mounting.

CM rates this gun at 770 m/s with a penetration of 104 and 96 mm @ 100 and 500 meters respectively (30 degrees).

So, how do these 4 guns related to one another?

Is the PaK39 somehow more closely related to the PaK40 than the KwK and StuK?

What design details motivates the three different performance ratings of the PaK39, the KwK40 and the StuK40, that all fire the same ammunition (identical projectile and casing that is) and, to the untrained eye, looks like the same basic weapon.

I'm not trying to pin errors on CM it's just that I have not been able to find out what is what despite sitting ankle deep in books dealing in detail with the vehicles carrying these weapons.

M.

[MajorBooBoo]

Is the 7.5 cm L24 used in the panzer IV and stugIIIb (early one) the same performance? What about the Panther vs late JagdpanzerIV? I lost the PS in my main computer and only have the craptop right now (no CM available).

I read that the 75mm PAK L46 had ammo as long as the panther KWK (but it was just strait and didnt have the panther case bottle shape). The panther AP shells were also different from the other ammo in that it had two bands and a different shape. At first it was the same then it was improved. That came from an encylopedia of german tanks btw.

I always thought that all the L48 and L43 weapons were about the same performance. They used the same ammo in both types. Did Jagdpanzer get a greater share of tungsten ammo perhaps?

[Mattias]

Yes and yes on the first one..

And yes they look the same size. Chamberlain, unfortunately, does nothing to clarify for me though, as he pretty much lumps all the 75mm L/43-L/48 together. Sure they are similar, but what are the differences? And just to clarify, my question was not related to any other 7,5 cm gun than the L/46 and L/48.

The order of priority was most likely Panzer, Panzerjäger SP and Panzerjäger motZ.

Late in the conflict the types of ammunition available ranged from the Panzers seen a few "40" grenades now and then, to the motZ's who would have found themselves firing HL grenades instead of regular AP on may occasions. Incidentally two situations that are not covered in CM:BO.

M.

[ February 20, 2002, 02:57 PM: Message edited by: Mattias ]

[MajorBooBoo]

http://ourworld.compuserve.com/homepages/willphelps/Specs-03.htm

This page seems to claim that there is a slight difference between L43KWK and L48KWK. The AP39 MV being slightly less for the L43.

If the L46 had a higher MV and the same shell, it should have more penetration too. But I get your point, you are asking if there is soem error in hetzers, etc? They essentially have a panzer IV gun, correct?

[ February 20, 2002, 05:18 PM: Message edited by: MajorBooBoo ]

[MajorBooBoo]

This is from:

http://www.geocities.com/pzfahrer/autopsy.html

Autopsy of a Hetzer.

It shows the bottle neck type rounds used in the hetzer pak39.

[Mattias]

The German guns in the L/43, L/46 and L/48 "family" have slightly different capabilities for obvious, and slightly less so, reasons.

My question is:

Why are there three different interpretations in CM, PaK39, KwK40 and StuK40 of what appears to be the same weapon, the 7,5 cm L/48?

Different armour penetration that is...

There are differences in their designs but from what I have seen none of these seem to be of the kind that affects the capability of the projectile fired to defeat armour.

M.

[MajorBooBoo]

7,5cm KwK37 L/24

7,5cm Stuk37 L/24

7,5cm K.37

7,5cm K.51 L/24

7,5cm StuK L/33

7,5cm K. L/40,8

7,5cm KwK40 L/43

7,5cm Stuk40 L/43

7,5cm KwK40 L/48

7,5cm Stuk40 L/48

7,5cm Pak40 L/46

7,5cm Pak39 L/48

7,5cm KwK42 L/70

7,5cm Pak42 L/70

7,5cm Stuk42 L/70

7,5cm KwK44 L/36,5

Heres a list of tank/panzerjager weapons for main guns that I stole. The germans did have a slew of 75mm weapons

[ February 20, 2002, 11:48 PM: Message edited by: MajorBooBoo ]

[Brian]

Originally posted by Mattias:

The German guns in the L/43, L/46 and L/48 "family" have slightly different capabilities for obvious, and slightly less so, reasons.

My question is:

Why are there three different interpretations in CM, PaK39, KwK40 and StuK40 of what appears to be the same weapon, the 7,5 cm L/48?

Different armour penetration that is...

There are differences in their designs but from what I have seen none of these seem to be of the kind that affects the capability of the projectile fired to defeat armour.

M.

As MBB aludes to, the three different guns had, despite the same length barrels, different shaped chambers and hence cartridge cases. The shape and size of a chamber determines, along with barrel length the rate at which the powder burns, so hence the velocity of the round.

They may all fire the same projectile but they fire it at different velocities and accelerations.

This is why for the British, the 17lb and the 77mm may be of the same calibre (both are 76.2mm) and they may fire the same projectiles but their rounds are very different. The 17lb being an artillery weapon, its case tends to be long and thin, which is close to the optimal for the burning of powder to provide a constant acceleration throughout the length of the barrel. The 77mm, being a tank gun and designed to overcome the associated problems with trying to cram the 17lb into a tank turret, has a shorter, more stubby case. That makes it easier to handle in the cramped confines of a tank turret but because it also has a slightly short barrel, in order to achieve the same velocities it must burn its powder faster. A short stubby case provides more surface area for the powder to burn and so a faster acceleration.

Whereas in a tank, the mass of the vehicle can absorb the sharper recoil, on an artillery piece, such a sharp recoil requires a heavier mounting, and so decreases the utility of the weapon.

So, basically there has to be a tradeoff. In the case of the German 75mm, they essentially designed different weapons, all utilising the same projectiles, rather than utilising the same weapon, for all roles, in all mountings.

Now, here's a comparable question. What is the difference between a Pak40 and a late war Pak36®, apart from the obvious one of calibre?

[ February 20, 2002, 09:40 PM: Message edited by: Brian ]

[Brian]

Originally posted by MajorBooBoo:

7,5cm KwK37 L/24

7,5cm Stuk37 L/24

7,5cm K.37

7,5cm K.51 L/24

7,5cm StuK L/33

7,5cm K. L/40,8

7,5cm KwK40 L/43

7,5cm Stuk40 L/43

7,5cm KwK40 L/48

7,5cm Stuk40 L/48

7,5cm Pak40 L/46

7,5cm Pak39 L/48

7,5cm KwK42 L/70

7,5cm Pak42 L/70

7,5cm Stuk42 L/70

7,5cm KwK44 L/36,5

Heres a list I stole. The germans did have a slew of 75mm weapons

You appear to have missed a few:

7.5cm Pak41

7.5cm Pak97/38

7.5cm Pak50

7.5cm Geb K15

7.5cm Geb G36

7.5cm FK 16 nA

7.5cm le FK18

7.5cm FK38

7.5cm FK 7M85 (Wansee)

7.5cm FK 7M59

Then there were a whole slew of various captured 7.5cm weapons the Germans utilised.

[Mattias]

Originally posted by Brian:

[QB]

Absolutely Brian. I think I covered this aspect in my first post though, referring again and again to the cartridge case size.

To clarify again: These three guns (PaK39, KwK40 L/48 and StuK40 L/48) that appear to be the same weapon, as far as performance goes, have all been given different stats in CM. Why is that?

I can't say but I'd love to hear from somebody that knows.

M.

[ February 21, 2002, 04:58 AM: Message edited by: Mattias ]

[MajorBooBoo]

I would also like to know why the L48s are rated differently.

The L48s all share the same ammo and the same length. The chambers then would all be the same. The only real difference is the muzzle brake which doesnt play into the performance. I didnt 'alude' that the L48s have different ammo or shells or barrel length (in fact I posted a pic that shows the hetzer PAK39 L48 USES bottle shaped ammo). The L46 PAK40 has different ammo but the L43 and L48 share ammo. Theres a difference in MV between L43 and L48 thats slight.

Perhaps its a typo because of the PAK name.

Did the german 37mm PAK and KWK share ammo (performance)? Did the german 50mmPAK and KWK share ammo(performance)? The 75mm PAK40 was different thats for sure.

[ February 21, 2002, 10:01 AM: Message edited by: MajorBooBoo ]

[K_Tiger]

Brian:

® means allways captured russian eqipment/guns...

[JasonC]

First there is what CM does and why it is incorrect. Then there is what was really happening. Here is the story as near as I can figure it. I am perfectly willing to be corrected if any of it is inaccurate.

The following German 75mm vehicles in CM are given a muzzle velocity of 792 m/s, which is correct for the PAK 40 75L48 - towed 75mm, Hetzer, Jagdpanzer, Marders. The following German 75mm Vehicles in CM are given a muzzle velocity of 750 m/s, which is (approximately) correct for the 75L43 - Pz IV G, H, and J. The following German 75mm vehicles in CM are given a muzzle velocity of 770 m/s - all StuG - which does not correspond to any of them directly, but is a compromise figure half way between the 75L48 and the 75L43.

All the rest of the penetration numbers accurately reflect the muzzle velcotity difference. The 4-8% difference in performance between CM Marders and CM Pz IVs tracks the difference you would expect between 75L48 and 75L43.

Here is my theory of the error. The PAK 40 numbers are looked up, and the figures are for the 75L48 just as it should be. The design info for the Hetzers, Jagds, and Marders in each case correctly notes the mounted weapon as a PAK 40 variety (although, truth be told, the PAK 39 was used for the Jagds, its performance is similar).

Then for the Pz IVs, they found the gun correctly listed as the KwK 40. Then the question arose, is the KwK 40 the same thing as the PAK 40? And the answer is no, especially in the *first* model Panzer IVs to mount it - the F2 and early G models. Those had the KwK 40 75L43. My guess is that BTS assumed that the KwK 40 differed from the PAK 40 and that was the difference between them.

Then there is the StuK 40 used in the StuG. Was it like the KwK, or like the PAK? Not clear, so they compromise and give StuGs the intermediary numbers. This confusion might be furthered by some sources calling later 75mm AT guns L46, suggesting that an intermediary length gun existed.

In fact, the L46 designation refers to the same gun as the L48. The difference is national variations in how the total barrel length is measured (including what part of the chamber, etc). Thus, for example, the Actung Panzer site lists the guns in Marders as PAK 40 75L46. The real difference, as opposed to the nomenclature difference, is between the early L43s and the later L48s. The early L43 length was used for both KwK 40 and StuK 40.

But that is the real source of the confusion. Unlike other nations, the model number of a German gun does not refer to one type only, but to a whole series made by the same companies and for the same purpose. The KwK 40 is a model number, and includes *both* L43 early versions and L48 later ones. The later ones are still referred to as KwK 40, there is no shift in the model designation. Or rather, the full model designation of one is the KwK 40 75L43, and of the other is the KwK 40 75L48. Note that there never was a PAK 75L43, only KwK and StuK 75L43.

The actual production history of the use of L43 guns was as follows. The first 200 long 75 Pz IVs, F2 series, used the 75L43. These were produced in March and April of 1942. So did 1275 of the next "G" series Pz IVs, produced from May 1942 through February 1943. The last "G" series Pv IVs, in March and part of April 1943, switched to the longer L48 gun. Then all Hs and Js had the L48 gun.

Meanwhile for StuG, the "F" series of 330 vehicles from March to September 1942, used the L43 gun (E and earlier had short 75L24), except for the last 30 vehicles, which used the L48. Then the model designation was changed to F-8, and 334 additional L48 StuGs were produced, through December 1942. Production then switched to the "G" model, all of which were made with 75L48 - as were later StuG IVs (from December 1943 onward).

Thus, by March of 1943, fielding of L43 guns had ceased. The KwK and StuK were from then on no different from the PAK 40 versions used towed and in the Marders and Hetzers. Of the vehicles depicted in CMBO, the only ones that might still have 75L43 guns would be "G" series Panzer IVs, originally produced between May 1942 and February 1943. Few can have still been in service in the west. At least 3/4 of the Pz IV longs produce to the time of the CMBO campaign had L48 guns, and the ones with L43 were far older, and thus had far longer to be KOed in combat.

So, what we should really see in CMBO numbers is all of them using the penetration table you see for the Marders, Hetzers, Jagds, and towed PAK. At most, the "G" model Pz IVs might use the table you see for the StuGs or the Pz IVs, to reflect either a portion of them, or all of them, having the L43 gun.

In CMBB, we should see the numbers you now see for Pz IVs, for the 1942 model long 75 AFVs, except for the Marders. Or, in other words, the CMBO numbers are correct for the time of *introduction* of the long 75s, but low for the Pz IVs and StuGs actually in service by the time of CMBO.

Now, as to the real variations in German 75mm gun types, there is also more to be said, though not on the subject of 75L48 vs. 75L43 confusions. Most of the varied types of 75s listed by others refer to infantry guns, howitzers, mountain guns, etc - all remote from the main subject here. There were however variations in German PAK models, used as dedicated PAK.

In 1942 and early 1943, the Germans fielded a number of weapons they designated the PAK 97/38. These were captured French 75s, originally designed way back in 1897 (hence the 97), mounted on gun carriages of German 50mm PAK 38s (hence the 38), modified of course to accept them. The Germans then added muzzle brakes, and reinforcing bands around the chamber, to enable larger charges to be fired.

The resulting gun was a 75L36, medium velocity field gun, with about the same capabilities of the Russian 76mm tank gun, or the US short 75. Several thousand were made, and in 1942 they were about as numerous as the purpose built and higher velocity German 75L48 PAK 40. Ammo production for them was also extensive. They were undoubtedly used as field guns (the original purpose of the French 75, of course), after the 1942 AT crisis had passed.

The Germans also made use of captured Russian divisional guns, 76L51 caliber. Note, this is a significantly larger and higher velocity gun than the shorter Russian 76mm tank gun, which was only medium velocity. They used these in two ways, not one.

Unmodified and firing captured Russian ammunition, they were designated the 7.62cm FK 296(t) - a field artillery piece designation. A limited number were rechambered to accept German PAK 40 ammunition, for use as dedicated PAK. These were called the PAK 36®. About 560 were made for towed PAK use, and another 600 were mounted on Marders. Note that both are small numbers compared to the overall number captured. The Marder version was nevertheless significant in 1942, because it was one of the earliest AFVs with good AT capability.

In 1944 the Germans fielded a number of 75mm AT guns designated the PAK 39. These were about as numerous as the PAK 97/38 had been, but coming out later in the war were dwarfed by the much larger numbers of PAK 40 models fielded by then. This gun was also used in the Jagdpanzer IVs (not the Jagd-70s, however). Its performance seems to have been similar to the PAK 40 - it was another 75L48 size weapon - but it is a potential source of confusion and I have found relatively little info on it. Everyone seems to treat it as equivalent to the PAK 40 L48.

The PAK 41 was the largest attempt to field "squeeze bore" cannon to achieve higher muzzle velocities. It was not a success, due to scarcity of ammo and the excessive barrel wear the technique caused. Only tiny numbers were therefore built.

Another rare type was fielded in 1944 and into 1945, the PAK 42. This was a towed version of the L70 gun in the Panther and Jagdpanzer-70. Around 1500 were fielded, late, or about 5% of the 75mm PAK in the second half of the war.

I hope this clarifies things. I agree that the CMBO numbers are not justified. They should all be more like the towed 75 and Marder numbers. The lower ones you see reflect the performance characteristics of the 75L43, for the Pz IV figures, and a compromise between the two for the StuG figures.

Apparently not everything was known when they were set. I trust it will be corrected for CMBB, when these differences mattered rather more (75L43 and 75L48 having different ranges at which they penetrate T-34s, e.g.).

In CBMO, the main difference that results from the slight undermodeling of the Pz IV gun comes when they face W model uparmored Shermans at medium range. The W model front armor defeats the L43 modeled Pz IV gun more readily than it should, with full L48 modeling. The result is a "sweet spot" for the Pz IV at 1100-1250 meters, where both need turret hits, while the Sherman W outperforms at 750-1000 meters.

For what it is worth...

[MajorBooBoo]

http://homepage.tinet.ie/~nightingale/indepth_75mmat.htm

Heres a PAK40 antitank gun website page. I am not sure if I follow everything so just want to lay out what I think I know..

stug III, stug IV, Panzer IV, JagdPanzer IV (early) and Hetzer are the same weapon:

They use a L48 weapon with a MV of 750 M/s. Doesnt matter if its called PAK or KWK or STUK, same weapon and same performance.

SOME stugIII and Pz IV used L43 but its nearly the same weapon (actually shoots the same ammo) and has a MV thats slightly less a 740 M/s

The actual PAK40 ATG (in the webpage) is a different beast. It has a MV of 792 M/s and fires its own unique ammo (but perhaps the projectiles were common?). It is only used in Marder type vehicles, RSO type mounts and rare things like the 234/series armored car. It isnt used in Stug or hetzer or tanks. Its more powerful and was alot more common than most think. 1,000 a month being made at some times.

The germans really should have made common ammo for the vehicles and the ATG. It would have made these discussions easier at least.

I think BTS can comment and perhaps set the record strait?

[Mattias]

It’s worth a lot Jason! I’ll be back tomorrow with a few comments.

M

[Claus B]

A bit of 7,5cm gun history that might clear up a few things.

First of all, the Germans measured the length of the gun from the rear face of the breech to the end of the barrel, not counting the muzzle brake.

The 7,5cm PaK 40, the towed anti-tank gun had a calibers length of L/46. The rifled part of the barrel was 2470.5mm long, the chamber 729,5mm. That plus the rear of the gun from chamber to end of breech amounted to a total length of 3450mm = 75mm x 46.

It used a 716mm long and slender cartridge case.

This gun was also used in some of the Marder self-propelled anti-tank guns.

Then came the 7,5cm KwK 40, the gun used in the Panzer IV. It was based on the PaK 40 and initially used the same barrel, i.e. the rifled part. The reason was probably to simplify logistics. The breech end of the gun was different though, using a shorter, fatter cartridge case 495,1mm long.

So, this leaves us with the rifled part of the barrel being 2470,5mm, a chamber that is 507,5mm + the rest of the breech end for a total length of 3233mm = 75mm x 43 (well, actually x 43.106 but you can't used that in a designation )

Early in 1942 tests were carried out with a KwK 40 with a longer barrel allowing a simpler rifling. It was intruduced from about August 1942 as the 7,5cm KwK 40 L/48. The numbers were: rifled part of the barrel 2852,5, chamber 507,5 + rest of gun for a total length of 3615 = 75mm x 48 (really 48,2 but again..... )

The KwK 40 was used in the Panzer IV, in modified form as the StuK 40 in the StuG III and IV (same length and ammo).

The PaK 39 was another development, but used the same dimensions as the KwK 40 L/48, the same ammunition and was used in the Hetzer and Jagdpanzer IV.

As for muzzle velocities, there is a lot of conflicting data floating around, but the March 1942 tests of the KwK 40 L/43 and L/48 might give a clue to the difference. Given the same propelling charge and firing the same shell (PzGr), the L/43 reached 790 m/s while the L/48 reached 820 m/s. The charges used may not have been the same as used in the production ammo though?

The data I've seen ranges from 740-750 for the KwK 40 L/43, 740-790 for the KwK 40 L/48 and 750-790 for the PaK 40 L/46.

Would be interesting to know the propelling charge and type for the KwK 40 PzGr 39 ammo, PaK 40 PzGr 39 was 2,75kg Diglykolpulver, Rohrpulver.

Claus B

[JasonC]

Very useful Claus B. But I think the main issue is the MV achieved by the KwK 40, and my personal guess is that the confusion over the numbers various people cite is based on lack of awareness of the L43, L48 distinction, *among* KwKs. Not necessarily by BTS, mind, but by the people publishing tables and the like.

The most common figure I have seen for the L43 is 740 m/s. Everybody and his brother gives 790 m/s (or 792, which I suspect is a feet-to-meters rounding difference only) for the L48 in PAK form. When some cite 750 m/s for a KwK 40, I believe the number is for an L43. It fits (very close anyway), and there isn't a PAK 40 L43, so it is easy to take an L43 vs. L48 distinction for a KwK 40 vs. PAK 40 distinction. Indeed, that is simply correct - if the KwK in question is a KwK L43. But not, I think, if it is a KwK L48.

It is certainly possible that the KwK L48 only achieved ~750 m/s muzzle velocity, even with the same gun dimensions as the PAK 40, which achieved ~790 m/s. Perhaps smaller charges had to be used to deal with recoil, for example. That may be what BTS assumed was the case, and it would explain the numbers they give to Pz IVs that they ought to know sported 75L48 guns.

If that were the case, however, then the motive for mounting the L48 essentially disappears. It would only give 750 m/s vs. 740 m/s for the L43, not enough of a difference to care, let alone to switch over the two largest AFV production lines (StuG III and Pz IV chassis) in the middle of the biggest production push in history.

Whereas, the switch from L43 to L48 would be motivated enough to actually bother, if the result was a MV of 790 vs. one of 740 or 750. It is the difference between penetrating T-34s out to 1-1.5 km and longer, and only 750-1000m (the uncertainty being due to T-34 armor quality questions). It is a ~15% difference in muzzle energy, not a trivial one.

One theory requires that the Germans switched two high intensity production lines from one gun type to another, redesigning their two most common AFVs to accomodate the new gun type, to achieve an increase in muzzle energy of less than 3%. The other theory only requires that someone along the chain of testing and reporting used the KwK 40 vs. PAK 40 distinction to mean the L43 vs. L48 distinction, knowing there was no PAK 40 L43, and therefore (wrongly) assuming, that no confusion could result from doing so. It is clear to me which is the more likely explanation.

But if someone can produce definite evidence that a KwK 40 *L48*, explicitly identified as such and distinguished from a KwK 40 L43 in the same document or study, only achieved 750 m/s muzzle velocity, not 790 m/s (with standard PzGr 39 ammo, of course), then there will remain a puzzle and a quandry, despite my estimates of prior likelihood. Anyone aware of such a report should produce it.

[Mattias]

It looks now as though bringing the L/43 gun into discussion was necessary from the outset, to tie up the start in a manner of speaking. Originally I never even thought of mentioning it though as it is not included in CM:BO.

I think BTS just tripped slightly over all the numbers and weapons involved and came out with a slight, and easily corrected, limp.

After all, if the RL numbers can be pinned it is only a very minor thing to change in CM.

Now, Claus has taken up most of the finer point in the development of the guns in question, perhaps looking in the same well done book as I, Spielbergers "Begleitwagen Panzerkampfwagen IV". I'll just add a few points from that source.

The length of the barrels on the L/43 and PaK40 are identical but pretty much every other number is different. For example, the movement of the PaK40 in action is almost twice that of the KwK, 900mm compared to 485mm. Add to that the shorter loading chamber, 507mm compared to the 729mm of the PaK40 and you have a much more compact weapon.

The volume of the loading chamber is 3,5 liters in the PaK40 and 3,17 liters in the KwK, indicating a larger charge in the PaK40 ammunition adding to the perhaps more optimal combustion in the elongated cartridge case. Both of which would explain the higher capacity of the PaK40.

The reason for shifting to the L/48 barrel was, as Claus has pointed out, partly simplify production of the barrel itself (less complicated rifling) and partly to gain the higher effect that could be achieved with the same powder charge as in the L/43 gun. The logistical strain of this change would appear to be minimal compared to the gains. Every extra millimeter gained could be the one that breaks the camels back.

That test Vo of 820 m/s for the 75 mm L/48 is certainly higher than average but on the other hand the Vo of 750 m/s sounds too low.

Looking through John Salts big penetration chart compilation I see the PaK40, the 75mm L/48 and the 75 mm L/43 being compared separately in most cases. The former two having almost identical numbers while the latter, L/43 gun, trails by up to around 4-10 millimeters depending on range.

Again the KwK40, the StuK40 and the PaK39 are all considered identical. Which I still think they were from a performance standpoint

Anyway, another interesting titbit from Spielberger concerns the design of the muzzle break to be used on the new KwK40 design. A representative from Krupp reported that the "ball" shaped muzzle break would be mounted initially for, apparently, no other reason than professional strife and competition among those responsible, as it was well know that the two chamber muzzle break was more efficient.

I for one think the shift to L/48 barrels had minimal impact on the line production of armoured vehicles whereas it simplified the production of the barrel and further optimised the performance of what turned out to be one of the best AFV guns of the war.

M.

[Mattias]

DP

[ May 05, 2002, 03:55 PM: Message edited by: Mattias ]

[Claus B]

Originally posted by JasonC:

The most common figure I have seen for the L43 is 740 m/s. Everybody and his brother gives 790 m/s (or 792, which I suspect is a feet-to-meters rounding difference only) for the L48 in PAK form. When some cite 750 m/s for a KwK 40, I believe the number is for an L43. It fits (very close anyway), and there isn't a PAK 40 L43, so it is easy to take an L43 vs. L48 distinction for a KwK 40 vs. PAK 40 distinction. Indeed, that is simply correct - if the KwK in question is a KwK L43. But not, I think, if it is a KwK L48.

I think you miss my point here. There is no "L48 in PaK form". The PaK 40 is an L/46 and uses the same barrel as the KwK L/43, the difference in calibers length comming only from the difference in chamber length.

Regarding the muzzle velocities, see below.

Originally posted by JasonC:

If that were the case, however, then the motive for mounting the L48 essentially disappears. It would only give 750 m/s vs. 740 m/s for the L43, not enough of a difference to care, let alone to switch over the two largest AFV production lines (StuG III and Pz IV chassis) in the middle of the biggest production push in history. Whereas, the switch from L43 to L48 would be motivated enough to actually bother, if the result was a MV of 790 vs. one of 740 or 750. It is the difference between penetrating T-34s out to 1-1.5 km and longer, and only 750-1000m (the uncertainty being due to T-34 armor quality questions). It is a ~15% difference in muzzle energy, not a trivial one..

The only thing that was changed between the KwK 40 L/43 and KwK L/48 was the barrel. The motivation for doing so was not to increase muzzle velocity, but to simplify production. The L/43 barrel used a more complicated increasing twist rifling while the L/48 had the same twist to the rifling from chamber to muzzle. The small increase in muzzle velocity was simply and added bonus.

Originally posted by JasonC:

One theory requires that the Germans switched two high intensity production lines from one gun type to another, redesigning their two most common AFVs to accomodate the new gun type, to achieve an increase in muzzle energy of less than 3%.

You are seeing problems where there are none. All that would be required was for the gun manufacturer to start using L/48 barrels once his stock of L/43 barrels ran out. It would have absolutely no implications for the StuG/Panzer IV production lines.

Originally posted by JasonC:

But if someone can produce definite evidence that a KwK 40 *L48*, explicitly identified as such and distinguished from a KwK 40 L43 in the same document or study, only achieved 750 m/s muzzle velocity, not 790 m/s (with standard PzGr 39 ammo, of course), then there will remain a puzzle and a quandry, despite my estimates of prior likelihood. Anyone aware of such a report should produce it.

Piece of cake Jason

Datenblätter für Heeres-Waffen, Fahrzeuge ung Gerät 1944 (ed. Pawlas):

7,5cm KwK 40 L/43 = 750 m/s

7,5cm KwK 40 L/48 = 750 m/s

7,5cm PaK 40 L/46 = 750 m/s

However, the data you can find is conflicting and harmonizing it would be to ignore that it probably come from a number of different sources, German, British and American and possibly from a number of different studies.

Here are a few more...

Bird & Livingston: "Armour and Gunnery":

75mm L/46 (PaK 40 L/46) = 792 m/s (2600 fps)

75mm L/43 (KwK 40 L/43) = 740 m/s (2427 fps)

75mm L/48 (KwK 40 L/48) = 750 m/s (24060 fps)

Senger und Ettelin: "Die Deutschen Panzer":

7,5cm KwK 40 L/43 = 740 m/s

7,5cm KwK 40 L/48 = 750 m/s

7,5cm PaK 40 L/46 = 792 m/s

Hogg: "German Artillery..":

7,5cm PaK 40 (PaK 40 L/46) = 792 m/s (2600 fps)

Jentz: "Panzertruppen.." vol II:

7,5cm KwK 40 L/43 and L/48 = 740 m/s

Chamberlain & Ellis: "Encyclopedia of German tanks..":

7,5cm KwK 40 L/43 = 740 m/s

7,5cm KwK 40 L/48 = 790 m/s

7,5cm PaK 40 L/46 = 790 m/s

The latter is the only one I could find, that bundles the PaK 40 L/46 and the KwK 40 L/48 and uses the 790 m/s figure for both.

A case could be made, I think, that the PaK 40 L/46 actually had a higher muzzle velocity than the KwK 40 L/43 and L/48 because the chamber volume was somewhat larger at 3.5 liters while the two tank guns only had a volume of 3.17 liters. There was room for more propellant, but whether it was used can only be decided if someone knows the amount and type of propellant used in the KwK 40.

A reduced amount of propellant would be consistent with the need for a shorter recoil in the KwK 40.

Claus B

Claus B

[MajorBooBoo]

http://ourworld.compuserve.com/homepages/willphelps/Specs-03.htm

This page also gives comparisons of the AP40 velocity and HE velocities for the L43 and L48 used in the Panzer IV. They are equal.

The AP39 velocity is 740 m/s and 750 m/s for the L43 and L48 respectively. Most sources I have seen put the L48's (stug, etc) at 750 m/s.

[Mattias]

5 minutes between us Claus

Do you have Speilbergers book? If not, where do you get your information on the development history?

M.

[MajorBooBoo]

Originally posted by Claus B:

The only thing that was changed between the KwK 40 L/43 and KwK L/48 was the barrel. The motivation for doing so was not to increase muzzle velocity, but to simplify production. The L/43 barrel used a more complicated increasing twist rifling while the L/48 had the same twist to the rifling from chamber to muzzle. The small increase in muzzle velocity was simply and added bonus.

There is also a maintenance issue. These progressive twist barrels wear out sooner. This would put an increased strain on the overloaded workshops in the field. The progressive twist actually is a sort of 'squeeze bore' technology that the germans went for in 88s and other high performance weapons. The 88 barrel was designed to be swapped out easily when worn out by changing the outer length that had the most severe increased twist.

It really would have been too much to service all the L48 weapons fielded.

[Claus B]

Originally posted by Mattias:

5 minutes between us Claus

Do you have Speilbergers book? If not, where do you get your information on the development history?

M.

You spotted the source with great skill and accuracy

I found some data on the amount of propellant used in the PaK 40 and KwK 40

7,5cm PaK 40 (Hogg):

Propellant for the PzGr 39 = 2.75kg

7,5cm KwK 40 (Spielberger):

Propellant for the PzGr 39 = 2.43kg

The propellant is of the same type in both rounds (Diglykolpulver, Rohrpulver)

It seems likely that there should be a difference in muzzle velocity given the 13% extra propellant used in the PaK 40 while any difference in muzzle velocity between the KwK 40 L/43 and L/48 can only come from the longer barrel - perhaps the origin of the 740 m/s vs 750 m/s?

A bit of speculation:

Regarding the Meppen firing tests in March 1942 where the KwK 40 L/43 reaches a muzzle velocity of 790 m/s and the KwK 40 L/48 a whooping 820 m/s, it could suggest that the guns were fired with using an amount of propellant similar to that of the PaK 40. As the barrel length of the KwK 40 L/43 and the PaK 40 L/46 was the same, the result would likely have been the same as well.

Under that assumption, the 820 m/s from the KwK 40 L/48 comes from the fact that the extra propellant made it possible to take advantage of the additional barrel length while the smaller amount of propellant used in the standard KwK 40 cartridge did not have any substantial effect on the muzzle velocity even when using the longer barrel.

Claus B

[MajorBooBoo]

Aren't sights designed depending on weapons characteristics? If there were that great a velocity increase, it would throw off the sights.

I have read of super-charging (extra propellent to)ammunition of weapons when they are outclassed. I believe the germans did it in the desert. The super ammo is held in reserve and only used as a last resort. I would suggest that extensive training with the ammo is out because of increased wear and operator damger/weapon damage.

Unless someone can produce information such as rifling differences (of PAK39 lets say) or something else, it would appear that ALL L48s had similar penetration performance. The L43 had nearly the same and the PAK40 ATG was superior.