German 75mmL43, L48 and L46 velocities

[Ratzki]

Just out of curiosity, what controls headspace in these large cal. guns? Poorly controlled ammunition headspace in a rifle affects accuracy, as well as chamber pressure so I am just wondering if this is an issue here as well.

[Mobius]

ORIGINAL: Ratzki
Just out of curiosity, what controls headspace in these large cal. guns? Poorly controlled ammunition headspace in a rifle affects accuracy, as well as chamber pressure so I am just wondering if this is an issue here as well.

I don't what headspace means. Is it anything like 'jump' or 'barrel whip'?

[Elron Hubbub]

They are rimmed cartridges. They use sliding block to close. The head space is then the thickness of the rim. Any adjustment would then be on the sliding block if any.

[Ratzki]

Would in the case that yoiu guys are discussing, could variations be the result of different manufacture of cases with slighth variations depending on where they were produced. I have to be very carefull with lot numbers in reloading rifle ammo.

[Ratzki]

Head space is controlled by some part of the case and is what keeps a constant distance between the case and the gun's chamber. In effect, all cases are fire formed to some degree as the case expands inside the chamber which is what seals the chamber so that no pressure is lost during projectile movement down the barrel. If the cases are not consistant then the pressures inside the case and down the barrel can vary which affects accuracy and velocity. Head space is also a projectile alignment tool to make sure that the projectile enters the barrel correctly. Some barrels like things one way yet another barrel of the same calibre can want things slightly different with reguards to headspacing.
There just seems to be alot of potential variations that are not known. Even positions of "gas checks" are not consistent between projectiles from the same company. Moving or adding/removing a gas check (I think they are called rotational bands in large calibres) is a huge game changer in velocity. I have had bullet manufacturors provide projectiles with very different gas checks with reguards to position and number. Some have crimping groves, some don't. These all came from the same company with the same style and weight bullets.
I think that unless you are using ammo from the same assembly line with all components provided from the same lots and being fired through the same barrel that you are going to have variations in performance.

[Elron Hubbub]

http://www.cruffler.com/trivia-October99.html

Hopefully, this can put us all on the same page.

The rimmed cartridge is dimensionally critical as far as the thickness and diameter of the rim. The rimless is critical in length diameter etc.

[Mobius]

Here's a link to a PDF of what I think is the source of those 1943 German graphs.
pretty big. 385M
https://www.dropbox.com/s/mzkvkd8wc64c3 ... 3.pdf?dl=0

Here is a sample of a German test.
(I converted 76 Kg./mm2 to BHN hardness.)

[Elron Hubbub]

That seems to be a collection of research papers dealing with other arms such as naval, aviation, etc. It's good stuff if you can decipher the German of those times.

The 3 shot group demonstrates the German method of testing. Shot 1 makes a dent and bounces off (NG), shot 2 is stuck in the plate (NG), and the final shot is a pass through and assumed to detonate inside. In reality, shot 2 would spray a good deal of fragmentation and could cause casualties and damage {edit: I looked at a larger blowup of the photos and it looks like the 2 shot may have actually broke off the welded penetrator piece and that may have entered also}. The Germans increased the velocity till they could get 5 repeatable results. They must have had a test fixture that allowed these high velocities (higher than a L70 weapon), and they used varying charges.

The German method seems to be the most stringent of all the combatants. Looking at the graphs, which shows 30 degree test results, one might wonder how a KWK40 or PAK 40 might have success against a T34 frontally. The answer to me is that the T34 has many weaknesses along with its highly sloped armor. Namely the hatch and MG and also shot trap. Combined with results like 2 in the test, the German 75mm weapons could not only penetrate the turret frontally, they could also do good damage to the hull. The Panther probably had it much easier as far as taking out T34.

[Mobius]

ORIGINAL: Elron Hubbub
The German method seems to be the most stringent of all the combatants.

Yes, it is more stringent. I produced a little program to calculate the US Naval Ballistic Limit (V50) and the German Penetration limit.
Halfway down the page link to .exe
http://www.panzer-war.com/page33.html
One additional difference is that the US number if normalized to 237 BHN armor while the German 200mm test armor is 217 BHN armor.

ORIGINAL: Elron Hubbub
Looking at the graphs, which shows 30 degree test results, one might wonder how a KWK40 or PAK 40 might have success against a T34 frontally. The answer to me is that the T34 has many weaknesses along with its highly sloped armor. Namely the hatch and MG and also shot trap. Combined with results like 2 in the test, the German 75mm weapons could not only penetrate the turret frontally, they could also do good damage to the hull. The Panther probably had it much easier as far as taking out T34.

The Russians tested it on the T-34 and it penetrated glacis up to 1000m.
http://tankarchives.blogspot.com/2014/0 ... links.html
The Yugoslavs tested it and it penetrated up to 1300m. Maybe different criteria. Maybe different muzzle velocity.

[Elron Hubbub]

The Germans did not use 30 degree in acceptance tests since they could not get the repeatable results that they were stuck on. That is, they 'needed' 5 consecutive shots to penetrate in a condition to detonate the HE filler. In reality, highly sloped armor introduced vaiables that were negligible in a 60 degree test. Not only ricochet but also damage to the base fused HE. Of course, they also consume more test plate since the angled shots need more distance between them. Also, the plate would tend to deform after successive shots.

IF we take the 30 degree data above in post 207, AND we assume that the Germans could indeed meet the 5 shot criteria, THEN I would probably be assured that they had a 'slow-crossover' and that there is a range where 2 and 3 and 4 out of 5 are achievable. It is not as well defined a velocity range like the 60 degree test. The Germans are being anal retentive it seems.

I also believe that the Soviet hard armor would produce casualty agents even when struck by a projectile that might penetrate but ricochets.

[Mobius]

This chart doesn't seem to be used to show what is reported in the datenblatt either. I've been trying to match the actual velocity at a range to the penetration reported and they aren't the same.
So the daten has the 75/L70 penetration as 138mm at 100m. The velocity of a V0=925m/s shell will be about 912m/s at 100m. That is 141mm from the chart.
The daten has the 75/L48 penetration is 82mm at 1000m. Also, German documents say the the impact velocity is 637m/s at 1000m for this shell. Which is 79mm from the chart.
I don't know what is going on with the differences. Maybe the Germans are normalizing the data for a constant armor quality like the US did.

[Mobius]

Here's a great find. Looks like a US chart that combines the ballistics of several 75mm German guns.
In fact it matches the Aberdeen data tables in the Hoffschmidt book. (I think, I only checked a few data points.)

[Elron Hubbub]

I suspect they used the wrong KWK 40 velocity. Instead of 2300 Fps, it might be 2500 Fps.

It is interesting that they are using all 3 weapons based on the 7,5 cm PzGr 39. The only real difference is velocity and two driving bands on the Panther projectile.

The German graph is using 2 variables, that is velocity and hardness. The test plates were different hardness depending on thickness. This accounts for the non-linear nature of the curves.

[Mobius]

Here's a better one:
The first one I posted (1944) was throwing all my ballistics off. It was correct down to around 2600 f/s then started to lose penetration and velocity too fast. It didn't match my Aberdeen data for the Pak 40 very well.

I found these on either a War Thunder or World of Tanks forum. There's another one from 1943 and has single gun of MV of 2400f/s so isn't much use.

This second one was produced in 1945.
Still they got the MV of the 75mm/L70 wrong as well as a the StuG 40.
I hope there is a chart from 1946 out there that corrects this.

Elron, your first post you asked if there are any orginal sources to the data. The answer is that there are a number. Not that many are very good.

[Elron Hubbub]

I asked what the "Ample Evidence" was. I have not seen much. And, if we look at these last couple of graphs, I really doubt many non-German information at this point.

[Mobius]

The last graph may be the source of the PaK 40 2600 f/s Aberdeen table. It matches pretty close, as far as I can read a line width and +/- 1mm. The line at the bottom with the tics at different ranges is pretty close, but not an exact match, to the German ballistics for 790m/s gun.

[Edit] It occured to me why the ballastics are not an exact match. The German velocity data is in m/s and the US is in ft/s. The German data could round off as much a 2 ft/s in either direction.

[Elron Hubbub]

Do you know what document they are from?

Aberdeen tested the Panther tank in 1946. They tested accuracy and I would assume penetration according to US standards. The Soviets 'tested' the initial Panthers captured at Kursk. This includes shooting one with a 8,8 cm L71 weapon and shooting a Elephant with the Panther gun (including using the rare AP 40 round). The Panther AP40 was not the same as a KWK 40 or Pak 40 BTW, it used the larger Pak 41 bolt inside.

I don't think I have seen much in the way of British testing. They must have tested especially after capturing weapons after Normandy. They certainly did reports on Africa battle weapons.

I think you are assuming data and should identify the source beyond "World of Tanks" posts.

[Elron Hubbub]

Here is a T34 that has been subjected to test shots from a Tiger 8,8 cm KWK 36. The range is stated as 1500 meters. There seems to be clear penetrations on the lower hull and joint between the lower and upper hull, but the one 'perforation' next to the removed driver's hatch, I have my doubts. This is possibly a ricochet that had enough energy to crack the impacted area and drive armor inward.

[Elron Hubbub]

Here is a Panther that has been hit by an 'Elephant' gun. I am not sure of the range. It is stated as being a ricochet. The effects inside are devastating. A cone shaped area of armor is missing through the plate. This is an early (Kursk) Panther D and may have face hardened armor.

[Elron Hubbub]

So, my thought is that the Germans are just too rigid in understanding armor defeating weapons. Reports claim the T34 are "hard to burn" from the front aspect. Basically, it is hard to get the Pz Gr to get inside and explode. But, many weapons that have a T/D advantage could make soft kills by killing/maiming the driver, etc. So, a better way of expressing penetration on highly sloped armor is really just a percentage. Having a specification like 50% chance of penetration, and 50% perforation (any) is more realistic of expected effects. Again, it is too expensive to test this with real sloped armor, one must just do an initial investigation on what velocity that is and verify using 60 degree armor.

If a KWK 36 could make that damage at 1500 meters, I would be assured that a Pak 40 could also do that damage in the 1000 type range. I believe the 'Yugo' tests had just a "perforation" type 'spec'.

The Soviet hard armor may have actually made the T34 more vulnerable. Hardness is good to a point, then it leads adiabatic shear problems and failure at higher levels.