German 75mmL43, L48 and L46 velocities

[Yoozername]

I would need some documentation that shows the 75mmL46 PAK40 AP39 rounds actually showed a decreased powder-weight reported on the cartridge case. To me, that would be compelling evidence.

The Germans explored alternatives for the Pak40 ammunition, see my earlier posts, and they seemed to have dropped these . Everyone knows the tungsten rounds were pulled by 1944. They also seemed to have given up on HEAT rounds for the PAK40. The 'soft-core' W rounds were probably just used by Marder units for fast moving AFV like light tanks and armored cars etc.

So, by 1944, the PAK40 had to rely on AP39 and HE shells. It certainly simplified training. But, to downgrade performance for what ends? Save gunpowder? I don't think so.

The PAK40, from my understanding, used different rifling than the KWK 75mmL48. The PAK used progressive rifling and the KWK used uniform rifling. Interestingly enough, the early KWK 75mmL43 also used progressive rifling. Some say the PAK40 and KWK L43 actually shared the same barrel.

My thought is that the initial KWK 75mmL43 used a higher propellant charge with little to no issues. It basically was limited in recoil length given that the commander sat behind the gun itself. But once the uniform twist barrel of the L48 was substituted for the L43, the weapon had issues with extraction possibly due to the initial pressure buildup the quicker onset of rifling introduced. The KWK solution was to reduce the charge to a level that allowed the weapon to work and still give acceptable penetration. A bad solution in my opinion but the Germans evidently wanted to produce L48 barrels quicker. I suppose the barrels would also last longer. This is not much of a concern with PAK weapons which fire much less rounds over their 'life-time'.

But I see no evidence besides mis-types as far as PAK40 m/v being lower later in the war. Certainly, armor penetration would be lower also.

[Yoozername]

I ripped this off from wkammo website:

[Mobius]

I found this in the German Anti-Tank Troops book by Fleischer and Eiermann.
Line 'G' seems to be the weight in grams. Line 'K' is the date.

[Mobius]

Of all things. I was able to find a 75mm Datenblatt. This must be late war as the only HEAT round is the HL/C. One thing to say about WOT is they have players with access to archives.

[Yoozername]

I have seen that before at WK2ammo website. To be honest, it looks like someone's homework that was copied in a hasty manner.

Again, there is an issue here with the sight. If you notice the velocities for the HE and Tungsten rounds, they have not really changed. That is, 930 and 550 m/sec respectively. So , if the gun is actually zeroing with a 750 m/sec AP39 round, then the AP40 and HE are dependent on that AP39 round to set the sight. One does not fire a AP40 and certainly not a HE round when zeroing.

This again shows the need for a unique sight if the AP39 PAK40 round was degraded in performance.

Again, I would be more impressed if a Datenblatt for the round stated a velocity differential as well as stating a reduced charge.

[Mobius]

I'm going to have to concede that the ammo was weakened at sometime after plenty of the full strength rounds were in circulation.

Now, the question is: Should we try to model it? Or does it matter?

It also looks like the APCR was nerfed a bit too. Since that pretty much ceased production after Kursk it shouldn't affect any load outs.

[Yoozername]

What does "APCR" was nerfed a bit too" mean?

[Mobius]

ORIGINAL: Yoozername
I have seen that before at WK2ammo website. To be honest, it looks like someone's homework that was copied in a hasty manner.

Considering the typos and and over typing errors in typed or printed material during this period I've seen it probably is more accurate. During this time period most men did not know how to type.

[Mobius]

ORIGINAL: Yoozername
What does "APCR" was nerfed a bit too" mean?

From the Encyclopedia of German tanks the design muzzle velocity was 990m/s but it was measured later as 930 m/s.

[Ratzki]

Would not projectile length, weight and shape influence point of aim/point of impact? So between the different rounds there could be a wide gap in velocities, yet still reletively close targetting.

[Yoozername]

The AP39 projectile was the same for the the Pak40 and KWK L43 and L48 guns.

Translational velocities are in question. Rotational velocity might be different still.

[Yoozername]

Merkblatt für die Munition der
7,5 cm Sturmkanone 40 und
7,5 cm Kampfwagenkanone 40

The Merkblatt H. DV. 481/58, which is a late war document dated Oct. 16, 1944, covers the KWK and StuK 75mm ammunition. It gives a higher weight for propellant than I have seen in other sources. 2.5Kg for the Pzg39 round.

The 1942 Merkblatt for the Pak40 ammunition gives the weight of propellant weight of 2.75Kg. I am not aware if there is a later version of this document.

[Mobius]

This is a wierd duck the Pzgr. 40(w). Soft metal body. It gives the propellant charge as 2.25 kg. I don't know if the Pzgr 40 with the tungsten core would be the same.

I wouldn't classify this as APCR in PCO. It seems blunt nosed so the closest thing I can come up with is something like APBC.

[Mobius]

From my double secret Yugoslav 1950s tests pdf.
The target is a Sherman.
Unfortunately there are no velocities on any of these guns.

I don't know what use is that 40W round. It takes up a slot that could be used for something effective.

[Yoozername]

It's covered fairly well at WK2AMMO website. Also in Merkblatt für die Munition der
7,5 cm Sturmkanone 40 und
7,5 cm Kampfwagenkanone 40

Basically, it has the same ballistics as Tungsten round. It could be used on light/fast afv also. I suspect it stuck around after the tungsten ran out.

[Mobius]

I attached a zip of the gun mod for the 75mm Pak 40 and loadouts in the Mods secttion.

[Yoozername]

I have triple-secret Vietnamese uber-data...

[Yoozername]

http://www.scribd.com/doc/34767721/Ammu ... -in-German

The Pak40 ammo.

The Ub rounds are apparently training rounds. Weight-wise, matched to their respective combat rounds. I suppose they could be used for zeroing but no real proof of that.

The 'W' round is the soft-iron round that was weight-wise and somewhat 'ballistically' matched to the Tungsten (Hardcore) round. One could use these to take some first shots at a AFV and hopefully range in and immobilize it. The AP40 tungsten round could then be used to kill the AFV. The 'W' round had enough kinetic energy to knock-out most light armored vehicles and even penetrate some tanks. It was my impression that the actual number of rounds manufactured for both the Tungsten and 'W' rounds was quite small and made in 1943.

I have seen no real proof that Pak40 Ap39 rounds ever reduced their propellant charge. If anything, I am suspecting that the AP39 rounds for the KWK 7,5 cm L48 guns were actually increased at some point.

[Yoozername]

This is some interesting bunch of information.

If I read this correctly, it is stating that as far as the StuK. 7,5cm development, the original Sturmgeshuetz used the 7,5 cm L43 barrel as is commonly known by most armor buffs.

It also gives rifling twist information for the weapons. The StuK L43 barrel, as well as the PAK 7,5cm L46 antitank gun barrel, had a progressive or 'gain' twist. This is when the rifling starts out at a slower rate and gets tighter as the projectile moves down the barrel. Quite a few German weapons had this. The 88mm Flak and 105mm howitzer come to mind.

But what is interesting is that the document states that the initial StuK. L48 barrels ALSO had this progressive twist. It was later changed to the constant twist rifling in later L48 barrels.

Another interesting piece of information is that the progressive twist and constant twist do not end up at the same twist rate! The L43 starts out at 6 degrees and ends up at 9 degrees while the later L48 ends up at 7 degrees. IF the muzzle velocities of these two weapons were equal, or nearly equal in the 740 m/sec and 750 m/s muzzle velocities often quoted for the L43 and L48 weapons, THEN the L43 would almost certainly have a higher spin rate once the projectile came out!

Twist rate is almost never discussed by wargamers. I recently read through the Rexford book and it is not mentioned once. As an engineer, my understanding is that energy can only be put into a projectile through translational and rotational energies. That is why I have mentioned gunpowder weights as being a critical clue in this mystery. Looking at various penetration studies and results, without all the parameters involved, leads to conjecture at best.

Quite a few people state that the PAK40 (L46) and StuK/KWK 40 (L43) both had progressive twist rifling and some state they shared the same barrel. That is something to look into. I have the Chobham report on the G model Panzer IV with the L43 weapon. The barrel length does indeed work out to L43. The rifling length is not along the whole barrel by the way.

In any case, IF the KWK/StuK 40 used the same cartridge for the L43 and L48 (same projectile AND powder), AND the L43 had greater rate of twist, THEN it is HIGHLY unlikely that the velocities would be so close. The reason being that not only is the L48 a longer barrel but ALSO the L43 is putting more energy into its rotational spin.

[Mobius]

Funny that you should bring up twist in German guns. I noticed this when looking at the ballistics of the US 76mm.

Note - The text block is from the Handbook of Ballistic and Engineering Data for Ammuntion and the chart is from TM 9 1907.