Allied tank armor, quality control

[Peasant]

Wtf, my post got posted twice? Mods , pls.

I've checked this two different ways and I get 100m=757.2 m/s. Have you checked your algorithm against other Russian tables?

You are correct. I've made an error in my formula: I switched around the exponents 0,75 and 0,7 which lead to wrong values.
The correct velocities, calculated assuming K=2400, are these:

• V(m/s) Range(m)
• 757 100
• 716 300
• 684 500
• 601 1000
• 531 1500

Corrected plot:



Still, no matter what K we use, those two never align. It's probably worth to check if the terminal velocities of other german guns are (in)correct as well.

[Mobius]

It looks like the table doesn't show that the penetration of the 75mm KwK 40 of the Russian table is reduced because of the shell quality but because of incorrect formula and ballistics.

[Yoozername]

One report from summer of 1942....

Report of Panzer Regiment 33, dated 31 July 1942:

‘Penetration ability of the long 75mm gun KWK 40 /L43 panzergranate 39 against the T-34: The T-34 is cleanly penetrated at every angle that it is hit at ranges up to 1.200 meters’
‘T34: The T34 that was far superior to the German Panzers up to the beginning of the Spring of 1942 is now inferior to the German long 5 cm Kw.K. L/60 and 7.5 cm Kw.K.40 L/43 tank guns. After the Russians attacked the German Panzer forces in several battles with the T34 and received heavy losses, they didn't send the T34 tank against the German Panzers so long as they had a chance to with-draw’

This report, from Panzerwar website, shows L43 penetrating out to 800 meters with Pzgr 39.



I have taken the graph and made the red line correspond to a 750M/s muzzle velocity curve. At 800 meters distance, it corresponds to ~650 M/s velocity.

75p39800.jpg

The 'rot' has clearly differentiated itself from Pzgr 39 at this velocity. It has 'kneed-over' on its graph and approaches an asymptote. It would not penetrate at 800 meters if fired at a muzzle velocity of 750 M/s (assuming it has similar flight characteristics). That is, further velocity does not improve its penetration, and more than likely increases shatter. In other words, the 'rot' "never gets there".

[Mobius]

That is interesting but does the testing start out at longer ranges then shortens the distance? So it may not get to a point where the shells shatter.
Plus doesn't the range that penetration occurs go by the ballistic model that is being used? So what the testers think is 800m is occurring at 635 m/s.
For the Russian data of the 75mm KwK /L43 we don't know what the Russians think the MV was.

Here they are assuming the PaK 40 has a MV of 770 m/s. Maybe they assume all model 40 guns have the same MV.
https://tankarchives.blogspot.com/2014/ ... links.html

[Yoozername]

Well, mobius and I have been back and fourth on this KWK/StuK/Pak '40s' issue through the years.

A synopsis, basically, in 1942, the KWK and StuK 40 weapons were equipped with the L43 barrels initially. The Pak 40 was also equipped with the same barrel. It is called 'L46' due to the German designation of 'lange' being the distance between the inside of the breech to the end of the barrell. The extra 3 langes come from the cartridge case.

The KWK/StuK 40s shared the same ammunition. They powderweight of propellant is either 2.41 Kg or 2.43 Kg, depending on sources, initially. The Pak 40 initially had 2.75 Kg propellant.

Physically, if the propellant is the same type (I can double check this), they fire the same projectile, and have the same length of rifling (also the same progressive twist), then the Pak 40 HAS to have a higher velocity. Often quoted in the 790 M/s range for the Pak 40. For the KWK/StuK 40 it is often quoted as initially 740 M/s.

Late information shows an increase in KWK/StuK 40 to 2.51 Kg and Pak 40 lowered to 2.69 Kg. I have some evidence online if anyone cares.

So, any mention of 770 M/s could be a later version of the ammunition, and the L48 barrel. It could also be the Pak 40 with the later ammunition. Note that the L48 increase the length of KWK/StuK 40s over L46 rifled length 5 lange. So, it increases the 'pressure vessel', but they alos changed the rifling twist rate to a constant, not progressive twist.

there is the possible issue of Fur Tropen ammunition erroneously tested in non-desert conditions. Possibly why the British numbers being low.

[Yoozername]

That is interesting but does the testing start out at longer ranges then shortens the distance? So it may not get to a point where the shells shatter.
Plus doesn't the range that penetration occurs go by the ballistic model that is being used? So what the testers think is 800m is occurring at 635 m/s.
For the Russian data of the 75mm KwK /L43 we don't know what the Russians think the MV was.

Here they are assuming the PaK 40 has a MV of 770 m/s. Maybe they assume all model 40 guns have the same MV.
https://tankarchives.blogspot.com/2014/ ... links.html

It may certainly not shatter at longer ranges (lower velocities). See penetration numbers for the 7-5-cm-pak-97-38-l-36. But it would not penetrate the T34 either. Pak 97/38 even have field reports saying frontal attack against T34 were fruitless. The German comparison of the two rounds show it reaches a point of diminishing returns.

Round Shot type Weight (shot) Muzzle velocity Range
100 m 1000 m 1500 m
7,5 cm K Gr Pz (p) ABCPC-HE 6.80 kg 570 m/s 61 mm 58 mm

https://panzerworld.com/7-5-cm-pak-97-38-l-36

If you look at the graph I modified, bring the orange line to the right and intersect the Pak 40 line/range. The range at which it is effective jives pretty much with th yugo or soviet tests.

I have no idea if the Rot and 39 fly the same and scrub velocity. They are the same weight and would have the same MV.

[Peasant]

I take from this that the German 7.5cm K.Gr. rot Pz. is able to consistently penetrate in condition fit to burst 76mm/20° of RHA, at least a relatively soft plate.

[Yoozername]

I take from this that the German 7.5cm K.Gr. rot Pz. is able to consistently penetrate in condition fit to burst 76mm/20° of RHA, at least a relatively soft plate.

Yes, that is the Aberdeen tests I referred to. I believe the maximum velocity is only ~600 M/s. It says it is inferior to the US M61 against harder armor. Unfortunately, that is from a listing of tests but I have never seen the actual test data itself.

[critical mass]

Harder armor will induce more damage to the projectile, and the K.Gr. rot Pz. wasn´t very tolerant to projectile damage to start with. It´s quiete surprising that it was, after all, comparing relatively well with the 75mm M61 APCBC.

Velocity drop off should not be identic between Pzgr.39 (secant ogive optimized for supersonic and transsonic) and K.Gr. rot Pz (tangent ogive, optimal for subsonic)

[Peasant]

Harder armor will induce more damage to the projectile, and the K.Gr. rot Pz. wasn´t very tolerant to projectile damage to start with. It´s quiete surprising that it was, after all, comparing relatively well with the 75mm M61 APCBC.

Velocity drop off should not be identic between Pzgr.39 (secant ogive optimized for supersonic and transsonic) and K.Gr. rot Pz (tangent ogive, optimal for subsonic)

Very interesting info. I've decided to check and it seems like only the exposed cap part is ogival is shape, while the windshield itself is just straight truncated cone(well, close anyway) , rounded on top. And yes both drawing are scaled for the same DPI values, I've checked.
Just thought I'd share this, might come in handy for other people researching this.

[Peasant]

Source: "The Science of Armour Materials, Ian G. Crouch"

[Peasant]

Something interesting came up, seems relevant to this thread: https://apps.dtic.mil/dtic/tr/fulltext/u2/a954836.pdf
I'll just leave it here.

[Avalancheon]

Something interesting came up, seems relevant to this thread: https://apps.dtic.mil/dtic/tr/fulltext/u2/a954836.pdf
I'll just leave it here.

Peasant, do you know of any WAL reports that were written about the Sherman? I was curious about the armor quality on the early variants. I recall hearing there were lots of manufacturing defects during 1942-1943.

[Peasant]

Peasant, do you know of any WAL reports that were written about the Sherman? I was curious about the armor quality on the early variants. I recall hearing there were lots of manufacturing defects during 1942-1943.

This would be an interesting read: https://apps.dtic.mil/dtic/tr/fulltext/u2/a954805.pdf

Here are some I have found by a quick Googling session:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a954476.pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/a954932.pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/a954836.pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/a954260.pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/a954171.pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/a954814.pdf

If you need more you can probably find them yourself, its not like I have access to any documents anybody with the Internet access doesnt.

[Peasant]

Using this data as reference, I've made some estimates on the effectiveness of US cast armour, specifically M4A1 Sherman tanks, against soviet blunt headed AP shells:

45mm BR-240:

38,1mm/60° PTP: 720m/s( 700m.); PSP: 763m/s( 500m.)
50,8mm/55° PTP: 852m/s( 100m.)

76mm BR-350A:

50,8mm/55° PTP: 551m/s( 1100m.); PSP: 599m/s( 600m.)
50,8mm/(55+30)° PTP: 609m/s( 500m.); PSP: 656m/s( 50m.)
38,1mm/60° PTP: 465m/s( 2100m.); PSP: 513m/s( 1600m.)

The 57mm, 85mm and more powerful guns have the PSP limit, even with additional 30° azimuth angle, equivalent to ranges over 1000m for the strongest part of the tank(UFP).