German 75mmL43, L48 and L46 velocities

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Yoozername
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RE: German 75mmL43, L48 and L46 velocities

Post by Yoozername »

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

Post by Mobius »

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

Post by Yoozername »

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

Post by Ratzki »

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

Post by Mobius »

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.
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RE: German 75mmL43, L48 and L46 velocities

Post by 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?

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RE: German 75mmL43, L48 and L46 velocities

Post by Mobius »

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

Post by Yoozername »

http://ww.battlefront.com/community/sho ... hp?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
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RE: German 75mmL43, L48 and L46 velocities

Post by Mobius »

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

Post by Yoozername »

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

Post by Ratzki »

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

Post by Mobius »

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

Post by Yoozername »

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

Post by Mobius »

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.


Image
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RE: German 75mmL43, L48 and L46 velocities

Post by Ratzki »

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

Post by Yoozername »

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/tme9369a ... 8mmgun.pdf

@Rat
Can you order solid steel shot with a FES driving band?
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RE: German 75mmL43, L48 and L46 velocities

Post by Mobius »

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.[:D]
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RE: German 75mmL43, L48 and L46 velocities

Post by Yoozername »

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

Post by Yoozername »

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?





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 )
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