RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities - 11/15/2012 4:55:47 PM

Yoozername

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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.

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RE: German 75mmL43, L48 and L46 velocities - 11/16/2012 1:26:13 AM

Yoozername

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Merkblatt f�r 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.

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RE: German 75mmL43, L48 and L46 velocities - 11/16/2012 1:52:52 AM

Mobius

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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.

Attachment (1)

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RE: German 75mmL43, L48 and L46 velocities - 11/16/2012 2:09:16 AM

Mobius

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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.

Attachment (1)

< Message edited by Mobius -- 11/16/2012 2:13:21 AM >

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RE: German 75mmL43, L48 and L46 velocities - 11/16/2012 2:12:37 AM

Yoozername

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It's covered fairly well at WK2AMMO website. Also in Merkblatt f�r 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.

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RE: German 75mmL43, L48 and L46 velocities - 11/16/2012 3:34:36 AM

Mobius

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

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RE: German 75mmL43, L48 and L46 velocities - 11/16/2012 4:58:17 PM

Yoozername

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

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RE: German 75mmL43, L48 and L46 velocities - 11/17/2012 6:23:37 PM

Yoozername

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http://www.scribd.com/doc/34767721/Ammunition-7-5cm-Pak-40-Anti-Tank-Gun-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.

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RE: German 75mmL43, L48 and L46 velocities - 11/20/2012 12:54:53 PM

Yoozername

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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.

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< Message edited by Yoozername -- 11/20/2012 1:01:03 PM >

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RE: German 75mmL43, L48 and L46 velocities - 11/20/2012 2:42:22 PM

Mobius

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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.

Attachment (1)

< Message edited by Mobius -- 11/20/2012 2:48:22 PM >

_____________________________

All your Tanks are Belong to us!
panzer

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RE: German 75mmL43, L48 and L46 velocities - 11/20/2012 3:22:21 PM

Yoozername

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The PAK40 rifling is progressive from 1/24 to 1/18. Have to research if that translates to the 6-9 degree values for the StuK/KWK 40 L43.

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 12:54:58 AM

Mobius

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So 1/32 has more twist than 1/40? In that case it is the spin that is allowing the better range.

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 1:47:01 AM

Yoozername

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That would be correct. It should be read "One revolution in 32 calibers". The projectile is only spun less than two times in the barrel yet it attains a signifcant RPM. On a HE shell like the 88mm weapon, which fires at 800m/sec or so, the actual centripital forces flinging out the fragmentation add a good amount of velocity to the fragments.

I would say that the added spin in the case of the US 76mm AP adds velocity by stopping velocity looss through AP rounds starting to wobble and nutation. The PAK40 AP would be spinning almost twice as fast than the US round.

Note that APCR rounds would likewise be spinning very fast. Rexford posted some accuracy data regarding these tunsten rounds and they showed better accuracy than what most people believed. I have seen some usage numbers of these AP40 rounds for 75mmL48 and they don't seem to have been hoarded. Considering the lack of heavy armor the Germans were facing (1943), They were probably being used because they were just so damn accurate and fast.

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 7:34:10 AM

Ratzki

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The faster the twist rate does not always equal a more accurate round. As rifling twist rates go up so does projectile rpm. In a rifle, bullets can reach 300,000 rpm and more. The centrifugal force caused by such high spin rates will exaggerate any defects/imperfections in the projectile that could have come from the manufacturing process or damage. These very small imperfections will make a bullet shot out of a high twist rate barrel very inaccurate and excessive bullet rpm's will cause even solid tungsten bullets to tear themselves apart in flight. You will also affect the impact angle with increased bullet rpm. If the bullet is too stable, then it is able to overcome it's shape which is designed to help the bullet impact it's target at the proper angle throughout it's arc of travel. Too stable a bullet will keep the bullet parallel to the ground when it should be tipping point down as it travels along it's arc and starts to fall like when you are targetting at long ranges and must aim above your target in order to hit it. There is a twist rate formula in my handloading books and I have found an online calculator that might be interesting

http://kwk.us/twist.html

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 2:53:41 PM

Mobius

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quote:

ORIGINAL: Yoozername
Note that APCR rounds would likewise be spinning very fast. Rexford posted some accuracy data regarding these tunsten rounds and they showed better accuracy than what most people believed. I have seen some usage numbers of these AP40 rounds for 75mmL48 and they don't seem to have been hoarded. Considering the lack of heavy armor the Germans were facing (1943), They were probably being used because they were just so damn accurate and fast.

I read somewhere that the German APCR design improved during the war. The first designs used the cores of the 28-20 squeeze bore. This was not that accurate. Primarily this was for the sizes up to 50mm. Later a better design was used. This primarily in the 75mm and better size.

< Message edited by Mobius -- 11/21/2012 3:06:26 PM >

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 3:25:14 PM

Yoozername

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Ratzki, you seem to be cutting and pasting 'info' regarding small arms? 300,000 RPM? This may be almost an order of magnitude greater than a solid shot 75mm WWII AP projectile might have. Do you think a solid shot 75mm AP round is going to tear itself apart from the spin rate?

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 3:51:30 PM

Mobius

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As for the accuracy of APCR the only round like that was thought to be more accurate than the normal round was the US HVAP. That may just because of the flatter trajectory. My ballistic model has German 75mm APCR with 50% more dispersion than the APCBC.

German Accuracy Firing
Type-------------------500m---1000m---1500m
75mm/L70-APCBC---100%------97%------72%
75mm/L70-APCR-----100%------56%------32%

I believe the source was from Jentz, Tank Combat in North Africa

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 4:14:43 PM

Yoozername

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http://ww.battlefront.com/community/showthread.php?t=43692

God, time flies.

I am not sure if he ever discloses his sources since he probably always had an eye on publishing or perhaps game design. In any case, I largely look at data like this and look at some of his use of "double dispersion" with doubt:

50% ZONES FOR VERTICAL AND LATERAL SCATTER
VERTICAL/LATERAL ZONE LENGTH FOR CONSTANT AIM
SINGLE VALUES OF DISPERSION

50L60 TUNGSTEN CORE
100m....0.05m/0.05m
300m....0.17m/0.16m
500m....0.30m/0.28m
800m....0.51m/0.49m

50L60 APC
100m....0.03m/0.03m
300m....0.09m/0.09m
500m....0.15m/0.15m
800m....0.26m/0.24m
1000m..0.33m/0.30m
1300m..0.47m/0.41m
1500m..0.58m/0.50m

Note:
At 800m range, 50% of the rounds fired at a constant aim will be within a box that is 0.51m high and 0.49m wide, which corresponds to a vertical distance of 0.26m above or below the mean impact point and a lateral distance of 0.25m right or left.

75L48 TUNGSTEN CORE
100m....0.1m/0.0m
300m....0.2m/0.1m
500m....0.3m/0.3m
800m....0.5m/0.4m
1000m..0.7m/0.6m
1300m..1.0m/0.8m
1500m..1.2m/1.0m
2000m..1.8m/1.5m

Note:
When only one decimal point is provided the figure has been rounded up or down. The actual figure may be up to 0.049m above or below the listed number.

75L48 APCBC
100m....0.1m/0.0m
300m....0.2m/0.2m
500m....0.3m/0.2m
800m....0.4m/0.4m
1000m..0.6m/0.5m
1300m..0.8m/0.7m
1500m..1.0m/0.9m
2000m..1.6m/1.3m
2500m..2.4m/1.8m
3000m..3.3m/2.3m

< Message edited by Yoozername -- 11/21/2012 4:58:00 PM >

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 5:19:49 PM

Mobius

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With Lorrin's posts of data you always have to try to determine if it is from a source or a calculation he ran.
I also found this in another post.

50L60 APC: 0.81m vertical and 0.73m lateral
88L56 APCBC: 0.98m vert and 0.56m lat
17 pdr APCBC: 1.19m vert and 1.01m lat
75L48 APCBC: 1.37m vert and 1.27m lat
1000m: 0.4m vert and 0.3m lat
1500m: 0.8m vert and lat

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 7:54:28 PM

Yoozername

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That is true. I often just asked him for the raw data.

I think I finally nailed him down when it came to the actual German gunnery test requirements for recruits. If his maths were true, then most gunners would flunk out. He realized that his application of 'double-dispersion' was scrogged.

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 8:14:41 PM

Yoozername

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http://forum.axishistory.com/viewtopic.php?f=47&t=99591&sid=b289add4dbad503b35f0ffc38c65b060

Interesting info

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RE: German 75mmL43, L48 and L46 velocities - 11/21/2012 8:52:51 PM

Ratzki

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quote:

ORIGINAL: Yoozername

Ratzki, you seem to be cutting and pasting 'info' regarding small arms? 300,000 RPM? This may be almost an order of magnitude greater than a solid shot 75mm WWII AP projectile might have. Do you think a solid shot 75mm AP round is going to tear itself apart from the spin rate?

The point I wa smaking is that there are several factors involved in gun accuracy. I would guess that the physics that applies to small arms might just have to apply in the big guns as well. Now that you have made a statement reguarding the spin rate of these 75mm rounds being of a lesser magnitude, what is the spin rate of one of the 75mm rounds? I don't know what it would be, but I was supprised to learn that it was this fast with a small calibre rifle. Accuracy goes up with faster twist rates at longer distances, there is also an increase in velocity as well. Longer barrels are less accurate then are shorter ones as a general rule because longer barrels vibrate more over their length and shorter barrels tend to be much stiffer. Not that said, firing over open sights is more accurate with a longer barrel, but with some form of optics, the reverse is true. As for velocity, once you have found the sweet spot for your calibre and bullet weight, often increasing velocity has a detrimental effect on accuracy. No here has even addressed head spacing, seating depth, compressed loads, types of propellant, ect.
In the end, I think that there are way to many unknowns to try to figure out what might have improved the accuracy of some types of rounds.
Oh, and as for the 75mm not being able to tear itself apart, I'll give in that a solid tungston round would be hard pressed to do this, as would the same be true of a small calibre bullet. But after lookin at all the pictures that you guys posted, it would appear that there are several 75mm projectiles that are no more solid then a small calibre bullet. Could these come apart?... What would stop them?

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RE: German 75mmL43, L48 and L46 velocities - 11/22/2012 9:09:47 PM

Mobius

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quote:

ORIGINAL: Yoozername
% ZONES FOR VERTICAL AND LATERAL SCATTER
VERTICAL/LATERAL ZONE LENGTH FOR CONSTANT AIM
SINGLE VALUES OF DISPERSION

50L60 TUNGSTEN CORE
100m....0.05m/0.05m
300m....0.17m/0.16m
500m....0.30m/0.28m
800m....0.51m/0.49m

50L60 APC
100m....0.03m/0.03m
300m....0.09m/0.09m
500m....0.15m/0.15m
800m....0.26m/0.24m
1000m..0.33m/0.30m
1300m..0.47m/0.41m
1500m..0.58m/0.50m

This data seems to be from German Firing Tables as I use it in my balltistics program. The range, velocity and dispersion in that post are real data AFAIK. Lorrin also includes his 25% ranging error calculations for accuracy in the post. I use some of his formula as well.

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 3:38:18 AM

Yoozername

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There is no way that data has been distilled out. I would really like to see the original document.

@Rat
I don't take the 'small arms leap to real heavy weapons' leap that easily.

Steel shot is steel shot. Not lumps of lead nor jacketed lumps of lead.

Small arms are designed around a single velocity. ATG, like the PAK40, have to fire HE at a lower velocity, Solid shot at another, and Tungsten and W rounds at an even higher velocity. Artillery, with its bagged propellant,has to fire a range of projectiles at a range of velocities. The larger the projectile, the less spin is needed. But there has to be enough spin so that even with minimal charge, accuracy is maintained. Something like a modern 155mm weapon class fires a 650m/s projectile at 10,000 rpms. WWII ATG might triple that.

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 5:22:44 AM

Mobius

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quote:

ORIGINAL: Yoozername
There is no way that data has been distilled out. I would really like to see the original document.

No, it really is from German documents or US documents of captured documents. I recognize the format. I only have one and it is for the flak 88mm. Here is a snippet of the AP firing table.

Attachment (1)

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 5:05:53 PM

Ratzki

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quote:

ORIGINAL: Yoozername

@Rat
I don't take the 'small arms leap to real heavy weapons' leap that easily.

Steel shot is steel shot. Not lumps of lead nor jacketed lumps of lead.

Small arms are designed around a single velocity. ATG, like the PAK40, have to fire HE at a lower velocity, Solid shot at another, and Tungsten and W rounds at an even higher velocity. Artillery, with its bagged propellant,has to fire a range of projectiles at a range of velocities. The larger the projectile, the less spin is needed. But there has to be enough spin so that even with minimal charge, accuracy is maintained. Something like a modern 155mm weapon class fires a 650m/s projectile at 10,000 rpms. WWII ATG might triple that.

Not even close to true. Just a quick look through my reloading books for my 45-70 Gov't. gives me ten different weights of bullets from 300grains up to 510grains. Some of these weights have 3+ types of bullet construction from cast lead through partitioned and FMJ, solid copper alloy, and even solid tungsten bullets are listed. There are numerous shape types with variations of same shape types by bullet company. Cases by winchester, remington, ect., each with differing volumes to consider. I can load down to 1400fps and approach 2200fps. And all these will fire out my one lone gun, and I should be able to hit a 6" diametre Target at 200m consistantly in order to have any business out there hunting deer.
I am aware of all the differing possibilities there could be from an ATG with reguards to projectile variation. I think that the same laws of physics apply to all calibres equally. To reduce accuracy discussions down to a couple factors would make no sense. I can get variations in accuracy by using a Remington case vs a Winchester case where nothing else changes, on top of that cases from the same lot are not created equal and must be resized, deburred, ect. just to have a hope at consistant accuracy. As for a rifle just having to pick one of these and go, again there are lots of hunters out there who carry a moddified case to fire buckshot in case the see a grouse, then have their hunting round, and also carry a full charge round in case they see something that wants to eat them. All will be fired from the same gun. So back to your post on the 1st page where you protested some data that Mobiius posted because there would be no way that multiple velocities would be used due to training/sighting/performance issues. I do not find that this would hold true, if us silly hunters can do it with buckhorn sights while standing, I am sure that a AT gunner could figure it out without too much trouble.

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 6:31:03 PM

Yoozername

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Here is the 'reloading book' the German 88mm gunners get to choose from. Pretty sure that this discussion is in regards to military weapons and standard ammunition. Again, small arms need greater rifling rates.

http://www.lexpev.nl/downloads/tme9369agerman88mmgun.pdf

@Rat
Can you order solid steel shot with a FES driving band?

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 7:59:42 PM

Mobius

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I think we kind of concluded the 75mm/L46 early vs. late controversy. Unlike at some other sites that get into it no one lost an eye or a limb.

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 8:13:54 PM

Yoozername

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Well, I concluded that there is no indication of the powder weight ever changing on the PAK40 weapon (sources state 2.7-2.75Kg). If anything, there seems to be evidence that the L43/L48 ammunition did reduce the charge weight. I also think that it was again increased once the issues were worked out.

The 88mmL56 and PAK40 both had similar weight powder. I believe the 88mm was 2.7 KG.

There is some interesting information in regards to the L43 and L46 barrels. There is evidence they may actually have been the same.

So, maybe Mobius has his conclusions but I have mine.

I believe the L43 KWK weapon (and StuK) both had no isssues firing with the progressive twist barrels. Supposedly, the initial L48 barrels also had progressive twist and they also may have had no issues. The introduction of the L48 with the uniform twist is probably the start of the initial issues leading to the reduced charge. Whether this was from the brass plated steel cartridge cases sticking in the from too quick an onset of pressure or some other reason for sticking is speculation, but the reduction of charge, possibly from 2.5Kg to 2.41`Kg, evidently 'solved' the immediate sticking issue. I have read that L43 weapons were withdrawn and placed in secondary fronts or rear reserve. Obviously, if they used reduced charge ammunition, they would be less effective.

Is there any data or evidence regarding the Germans reducing the charge on the Pak40? Looking at confusing anectdotal penetration and velocity testing of used weapons seems to be what this thread, and other threads, are based on.

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RE: German 75mmL43, L48 and L46 velocities - 11/23/2012 8:32:04 PM

Yoozername

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This is data from the 88mm Flak gun. It is interesting to note that the 'L56' length that is well known, is actually describing the length from the inside of the breech (rear of a loaded cartridge) to the end of the barrel. It is more than likely the same for other German guns. So the 'L46' and 'L43' weapons COULD have the same barrel. The difference in 'L' being explained by the longer cartridge case of the PAK weapon.

Note the progressive twist also used in the 88. Not as aggressive as the PAK 40 but these Flak weapons probably fired many more rounds than a PAK normally would. The use of multi tube barrels probably was for changing out worn sections. These FlaK weapons were produced in great numbers. I don't know why the KWKL48 really needed uniform twist but who knows?

quote:

88mm L56
INTRODUCTION
Outer tube 785 lb
Inner tube 805.5 lb
Liner (muzzle section) 600 lb
Liner (center section) 199 l b
Liner (breech section) 58 lb
Retaining rings 34 lb
Over-all length of tube 185 in. (470 cm )
Over-all length of gun and tube 194.1 in. (493.8 cm )
Length in calibers 5 6
Distance from center line of trunnions to breech face_ 6.5 in.
Travel of projectile in bore 157 .4 in. (400 cm )
Volume of chamber 226 cu in.
Rated maximur'n powder pressure 33,000 lb per sq in. (approx. )
Muzzle velocity 2,690 ft per se c
Maximum range :
Horizontal 16,200 yd
Vertical 39,000 ft
Maximum effective ceiling 25,000 ft (at 70-deg elevation )
Rifling :
Length 157.4 in. (400 cm )
Direction Right-hand
Twist Increasing 1 turn in 45 calibers to 1 turn in 30 caliber s
Number of grooves 32
Depth of grooves 0.0394 in. (1 mm )
Width of grooves 0.1969 in. (5 mm )
Width of lands 0 .1181 in . (3 mm )
Type of breech mechanism Semiautomatic horizon -
tal sliding block
Rate of fire 15 rounds per min (practical rat e
at a mechanized target )
20 rounds per min (practical rate at an aerial target )