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

[Yoozername]

It would seem the Germans assumed that T34s late in the war would have 60mm frontal sloped armor at 30 degrees. The Panther Bible calls this out. Obviously, the Soviets did not do this and the Panther gun and other weapons could take on the 45mm @30 deg of the T34s.

[Mobius]

It would seem the Germans assumed that T34s late in the war would have 60mm frontal sloped armor at 30 degrees. The Panther Bible calls this out. Obviously, the Soviets did not do this and the Panther gun and other weapons could take on the 45mm @30 deg of the T34s.

That would be the T-34 Model 1942e.
https://en.wikipedia.org/wiki/File:T34_2.jpg

[Yoozername]

I think the up-armored T34, and the KV-1, were mostly used earlier in the war. Basically discontinued since it hampered maneuverability. But it must have impressed the Germans and they were assuming it would continue. So, the troops are correct when stating the Panther gun was more effective than they were taught as far as this documentation is concerned. The Panther gun could probably take out a T34 frontally on the 45mm sloped armor much further than 800 meters. I would expect a Pak 40 to do that. The side angle of the shot (obliquity) is not the correct answer.

[Yoozername]

And it has the infamous 770 m/s. This may mess up Christian's Pak 40 ammo evolution timeline.

Hopefully, you figure out your own timeline...

[Mobius]

And it has the infamous 770 m/s. This may mess up Christian's Pak 40 ammo evolution timeline.

Hopefully, you figure out your own timeline...

Hopefully we will add adjusted Vo timeline in a certain game I work on in the next update.

[Yoozername]

Does that matter now? How many people are even playing it?

[Mobius]

Admittedly the work is glacial, but it still is going on. It's a matter of principle. Plus I get to make use of some of the info I find here and elsewhere.

[Fboldcrow]

Hope I'm not off topic but what is the difference between the SruK34 and SruK40 75mm guns? Can they both fire the same ammo or is it like the 88's?

[Miles Krogfus]

Schusstafel H.Dv. 119/324 was first issued in August 1942, a revised version appeared October 1943, and was reprinted October 1944. Supplements were also issued. Below are three excerpts from the Oct 43/44 edition. Note that after the L/43 gun was discontinued, the Pak 40 L/46 got the same barrel rifling as the L/48.
I already have posted above the change in the Pak 40 APBC propellant resulting in a change of the official muzzle velocities for all the 7.5 cm guns from the 1942 Pzgr 39 770 to the 1943/44 750 m/s. Remember that the L/48 APCBC propellant amount was raised.
As more secondary companies got involved in 7.5 cm Pzgr 39 production, reports show up to a 10% difference for some APCBC in nose hardness for the Pak 40 (and a 12% difference for the Panther's Pzgr 39/42) which affected their performance.

[Mobius]

Thanks Miles, that clears up some things.

The test temperature is 10°C. Is there documentation on what the elevation or mm of mercury this is for?

[Denniss]

"60m über dem Meere" = 60m above sea level

[Yoozername]

Thanks Miles, that clears up some things.

It does but also brings things to light. I do not agree with all the statements...

I already have posted above the change in the Pak 40 APBC propellant (the amount of propellant for the hard core round also was lowered) resulting in a change of the official muzzle velocities for all the 7.5 cm guns from the 1942 Pzgr 39 770 to the 1943/44 750 m/s and the PzGr 40 from 990 to 930 m/s. Remember that the L/48 APCBC propellant amount was raised.
As more secondary companies got involved in 7.5 cm Pzgr 39 production, reports show up to a 10% difference for some APCBC in nose hardness for the Pak 40 (and a 12% difference for the Panther's Pzgr 39/42) which affected their performance.

...But, it does confirm some things. I had once said that I read that the rifling on the Pak 40 was changed. It was in another document. This data seems to show this was the case after the L43 weapons were discontinued. To review, the initial L48 were also rifled with the progressive twist, this was for the initial l48 StuGs, but it was quickly discontinued after a short run (400 pcs.?). The StuG III did get the L48 before the Panzer IV. In fact, the Panzer IV was produced with the L43 till early 1943. Some people claim that the Pak 40 and KWK 40 L43 used the same barrel itself as in a part number. IT just might be so. Clearly, given the use of L43 till the Panzer IV changeover in 1943, the Pak 40 must have changed also to constant rifling around this time at the soonest. It would make sense and Speer would agree.

An interesting thing in the document is that it shows that the 'Lange' number is actually a distance from the end of the barrel to the back of the breech. This is confirmed in the document. The document also shows that the 'travel' or actual distance the projectile moves after seating in the rifling, is another story. That is, the L43 and L46 travel are identical. The 3 'Lange' difference is actually another way of showing patronhulse or case length difference. And, comparing the L46 with the L48 shows a 5 'lange' difference, not 2. Which is the same as the L43 KWK 40 compared to the L48 KWK 40 (if you follow).

The recoil throws are interesting. In the case of the KWK 40 weapons, the KWK have a smaller recoil distance, than the StuK. This is, of course, with the same ammunition. I agree with the KWK 40 ammunition actually increasing in powder weight from it's initial form. i will get the documents but basically it went from 2.43 Kg to 2.51 Kg. One must be careful with these weights since it should reflect the total propellant. It is about a 3.3% increase. Most documents show this as using the whole volume of the cartridge. In April 1944, 2.51 Kg is again mentioned in a document which I will post. I rally doubt that they would decrease the KWK 40/StuK 40/Pak 39 ammunition's propellant after April 1944. And it would not be possible to increase unless changing the propellant itself.

Before discussing the Pak 40, I think we need to discuss the KWK 40 velocities themselves. Most documents claim a difference in the KWK 40 velocities as far as the L43 and L48 having different lengths (and rifling perhaps). For the initial 2.43 Kg KWK 40 ammunition, it is often claimed to be 740 M/s for the L43 and 750 M/sec for the L48. 770 M/s was not the initial velocity. If there is a document that says so, please share that. Having a 3.3% increase in propellant, and using a linear assumption, would push the L48 up to a ~775M/sec velocity. It is of note that the Germans did not distinguish between KWK 40s. That is, they were both 'KWK 40'. The Germans went through a few iterations of muzzle brakes for the KWK 40, BTW, and recoil is certainly an issue as far as getting the Panzer IV and StuG AFV to use these weapons. So, the question is...why the lack of difference in recoil throw? If anything, all things being equal, a L48 weapon has more mass (longer barrel), so why would it have the same throw as a L43? It's a legitimate question. The L48 would have the later and better muzzle brake also.

edited thanks to Dennis...

I will get data and post it before moving on to the Pak 40.

[Denniss]

document shows the Pak and L/48 weapons already with constant rifling, the L/43s with progressive rifling.
Recoil lenth is the same for KwK of both barrel types and the same for the StuK version of both barrel types, I assume this is due to different recoil mechanism owing to limited space in Pz IV turret

[Yoozername]

document shows the Pak and L/48 weapons already with constant rifling, the L/43s with progressive rifling.
Recoil lenth is the same for KwK of both barrel types and the same for the StuK version of both barrel types, I assume this is due to different recoil mechanism owing to limited space in Pz IV turret

Pak 40 had progressive rifling in 1942. So, it seems they changed that to a constant rifling.

The Panzer IV kept the L43, with its progressive rifling, till March of 1943 while the stuG III changed from L43 to L48 in Fall of 1942.

Yes, the Panzer IV did have shorter recoil, or the KWK 40 weapons had more limited recoil than the StuK 40. So, that is interesting in that recoil is the same for the difference in barrel. And using the two different Pzgr 39 ammunition.

[Yoozername]

Here is a document from April 1944 concerned with propellant weights. Note that it breaks out the propellant and booster weight. for the Pak 40, it is 2.73 Kg total, 2.71 Kg plus 0.020 Kg. KWK 40/StuK 40 are 2.51 Kg total. This is the latest war document concerning this issue that I have found.