German 75mmL43, L48 and L46 velocities

[Mobius]

ORIGINAL: Elron Hubbub
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'.

They are no different than the US with a 50% penetration level.

[Mobius]

I've been trying to find another German source for 75mm/L70 velocity data. I have two sources both are in Spielberger's Panther book. But they don't agree with each other. One is a graph. I overlayed it on what the US ballistic formula outputs.

Also, is an output of the 75mm/L48 using the same US ballistics formula. It matches within +/- 2m/s out to 2500m of the German tabular data of the 75mm/L48. So the US formula works for the KwK40. Just not sure why it isn't matching the 75mm/L70 data that I have.

[Elron Hubbub]

The large white circle on the T34 hull is from a 8,8 cm HE round. Supposedly tearing off the driver's hatch. The 8,8 cm HE was actually very high velocity and was used as a antitank weapon under certain conditions. Notably attacking side armor.

[Elron Hubbub]

ORIGINAL: Mobius

I've been trying to find another German source for 75mm/L70 velocity data. I have two sources both are in Spielberger's Panther book. But they don't agree with each other. One is a graph. I overlayed it on what the US ballistic formula outputs.

Also, is an output of the 75mm/L48 using the same US ballistics formula. It matches within +/- 2m/s out to 2500m of the German tabular data of the 75mm/L48. So the US formula works for the KwK40. Just not sure why it isn't matching the 75mm/L70 data that I have.

Yes, something is obviously wrong. Or, both curves can't be correct. Since the projectiles are virtually the same, the flight characteristics should closely match. One should be able to just 'slide' the characteristic curve for the L48 over to the 'Panther' curve at 750 M/s and they should be very similar.

The Germans would say so also. They tested by varying velocity.

This brings up the point of how they did test and record velocity. I imagine the method used magnetized projectiles that are shot through coils at a very precise distance from each other. The coils are monitored through a oscilloscope that can capture each voltage produced as the projectile passes through. It can then deduce the time and therefore the velocity. I am not sure how they actually did it in WWII but that is a common scheme. Did anyone do it for multiple points along the firing arc? That would be the only way to really determine a characteristic curve like you are showing.

[Mobius]

That's right. They test the guns by firing at a set range of 50 or 100 meters or yards but vary the charges to simulate different ranges. But if they don't have the ballistics of the shells right then they aren't really testing the penetrations at those ranges. Chronographs seem to have been developed during the war so the accuracy should have improved toward the end. Because of dispersion they couldn't place them very far away from the gun.

Shells of a particular type should have about the same ballistics fired from different guns. One thing to note is that when the US 76mm went to a higher twist the ballistics improved a bit. If the shell spun at a higher rate it didn't lose velocity quite as fast.
http://www.panzer-war.com/Images/M9190776.jpg

My ballistics formula is a short version of the US formula but is not as involved as the highly detailed 6 degrees of freedom used by the military.

[Elron Hubbub]

So, the Americans tested the velocity of the 76mm weapons out to 7000 yeards?

[Mobius]

Or, they worked out the ballistics to that range.

[Elron Hubbub]

So they measured to 5000 yards? They list a penetration value for that range?

[Mobius]

It's all there.
The way those graphs work is you draw a line up from your range value (along the bottom) until it intersects the velocity curve. Then draw line right angle from that point until it intersects the armor angle curve of your choice. Then draw line straight down from that point until it intersects bottom values and read inches of penetration.

[Mobius]

This is a clue on how the US came up with their ballistic tables. They fired at 1500yds and measured the time it took to hit it. Then worked out what kind drag number the shell must have to achieve that.

[Elron Hubbub]

ORIGINAL: Mobius

It's all there.

The dashed lines meaning some form of interpretation?

[Mobius]

ORIGINAL: Elron Hubbub
The dashed lines meaning some form of interpretation?

Just happen to run across this.

It will be noted that certain portions of the penetration curve are shown as broken lines. This represents an estimated performance for which actual firing data have not been obtained. The penetration curves are compiled for intact or shattered projectile, with the greater portion of the fragments, completely penetrating the plate.

[Elron Hubbub]

Been awhile.... In any case, I have a document that uses actual type-set print for April 1944...

Lots of good info in it. The numbers above the Pak 40 info are for the 7,5 cm L24 weapons from the previous page. The Pak 40 shows just the PzGr 39 as 2.73Kg of propellant. The KWK 40 shows 2.54 Kg of propellant. Many ammo types like HE and HEAT and Nb (smoke) show alternative propellant types to get the same velocity. This does not show for the German armor piercing ammo PzGr 39 or PzGr 40 for these 7,5 cm weapons. The document is concerned with explosives and propellants used in April 1944 in weapons that the German military is still fielding in some form.

It would seem that Hl/C (Heat) was common for most weapons at this time and they are listed separate from hl/B rounds.

I challenge anyone to produce any German document that shows that the Germans reduced the Pak 40 propellant as it must be in the case of a reduced velocity. In fact, if they did, then almost every type of ammunition would be using a cartridge that is too long. That is, there is no point to having a breech and cartridge that does not fulfill its potential in some ammunition used in it.

[Mobius]

This is worth posting.
Though the 1500m value of the Pak 40 pzgr39 is probably an error.

[Elron Hubbub]

I believe its been posted in this thread before? Maybe a review would be worth it since its been awhile.

It looks to be from December 1942? It is very interesting for a number of things. The last column, if I read it correctly, says that Hl/B was the most used ammo in Dez. 42?????? WAY TO GO Hl/B!!!!!

I have been thinking lately about just what exactly is meant by the German use of the specification "lange" (ex: L46). I think they mean the barrel length from the muzzle (discount the muzzle brake) to the actual point in the tube that the rifling begins. Some claim that there are different methods, i.e. that you measure from the muzzle to the very rear of the breech. This would make the Pak 40 a very 'short' gun because it had such a long case. Something to research.

As a quick example, in the case of the Pak 40, in the second column above, there is a length stated as 3700mm. If we divide 3700 mm by 75mm we get 49.33 as a number. So, if we subtract 49.33-46=3.33*75mm=250mm. This is about the length that a projectile protrudes into the barrel and the driving band is. In other words, L46 means 75mm*46=3450 and that is the travel or distance that the projectile is under pressure. If you look at the note for '+' it mentions Bodenstuck. I take that to mean that the rifling and driving band meet.

i am not sure all nationalities did it like this.

[Elron Hubbub]

tatsachliche lang +mm must mean what I describe...indeed length +mm

[Mobius]

ORIGINAL: Elron Hubbub
It looks to be from December 1942? It is very interesting for a number of things. The last column, if I read it correctly, says that Hl/B was the most used ammo in Dez. 42?????? WAY TO GO Hl/B!!!!!

I don't know all the load outs for PaK and KwK 75mm guns so some may not have HEAT for certain time periods. Right now there can only be one type of HEAT shell from each gun. So early war guns have the penetration of the HL/B and later models that of the improved HL/C.

[Elron Hubbub]

Hl/C is listed for most all weapons in April 1944. I would suppose that it was actually available a little earlier than that. It was supposedly liked by the Germans mostly because it could hole a T34 head on. But it still had the range/accuracy issues that most heat rounds had at that time.

In that chart from December 1942, it shows that Pzgr 40 for the Pak 40 are basically gone at that point. 'Bestand' means available currently or Stock. They shot off 5K in December though, so it was really a minority type compared to HE or AP or Heat. The Pak 40 'fleet' is also small at this time.

It is interesting that the Pak 41 'squeezebore' weapon is actually stocked with (W) rounds and using them. I always theorized that they would use these first as ranging rounds that could do some damage and stop a tank. The Tungsten carbide rounds are then used to finish that tank off.

[Mobius]

ORIGINAL: Elron Hubbub
It is interesting that the Pak 41 'squeezebore' weapon is actually stocked with (W) rounds and using them. I always theorized that they would use these first as ranging rounds that could do some damage and stop a tank. The Tungsten carbide rounds are then used to finish that tank off.

Maybe to scare the crew? In Middle East wars some Syrians bailed out of their perfectly good tanks when they were being pinged by Israeli Centurion ranging machine-guns knowing that a 105mm round was soon to follow.

I was hoping if we ever have a new PCO update or expansion HEAT shell evolution could be included. But, we haven't come up with a clean way to format this, which does not involve updating every single gun xml.

[Elron Hubbub]

There is a pic that shows a 7,5 cm KWK 40 HL/C that appears to be from january 1944. The powder date code is from the middle of 1943.





The Soviets were big users of light tanks. I suppose post-Kursk they cut back on them and used lend-lease tanks like the British Cromwell (57mm) in that role. So, HEAT and W (iron) rounds could take out light tanks easily and also other light vehicles like armored cars without using the expensive AP39 or AP40 rounds. A HEAT round on a SU76 would have been quite a sight.