Alternative light and anti-tank guns, 1935-45

[bf109xxl]

Quirk with this system is that one still uses the off-the-shelf ammo.
RT-20 was supposedly doing 850 m/s, despite the short barrel and the divertion of small % of the gasses.

I understand why it was necessary to complicate the design in this particular case (for use of standard large caliber ammunition), but with AT guns, why? Artillerymen will have to either jump into a trench or run a decent distance away from the gun every time it is fired.
If the percentage of gases used is low, there will be no large effect of recoil reduction. Conservation of momentum law. The Soviets played around with recoilless guns before the war, realizing that they require a lot more powder. And I'm not sure these tricks are even possible with caliber above 30mm.

 

[marathag]

But the Germans used heterogeneous armor with a medium hardness backside, and the Soviets used medium hardness armor (42SM, 52S) after the war.

British weren't able to examine newer armor from the USSR before the choice was made to deply all the various *BAT HESH tossing recoilless guns.
And turned out to be effective all the same, until the new Composite Armor designs were introduced

2nd, HESH could be fired thru rifled tubes, without effecting the warheads effectiveness, unlike HEAT.

 

[ThomasP]

Also, HESH did double duty as a HE round and was used as such - eliminating the need to carry an additional type of ammunition.

The countries that adopted HEAT rounds either carried dedicated HE rounds in addition to the APDS and HEAT - or developed HEAT/MP rounds to be used as a bit sub-par HEAT and HE.

 

[yosimitesam]

I'm still studying armor penetration - trying to understand how much the caliber of the projectile mattered, and how much the design of the projectile mattered for different types of armor and different thickness. Soviets used homogeneous armor of high (or very) hardness, even late cast Soviet armor was high hardness, Germans used heterogeneous armor (with rare exceptions at the end of the war), Americans used medium to low hardness armor with a high proportion of cast parts, etc. In some cases APCR was optimal, somewhere only a high hardness cap was sufficient. In addition to armor properties, the ratio of core size and armor thickness mattered. All this is time-consuming, but I still want to get some kind of overview for myself.
Some of the things that came across during my research: scans of Soviet reports (terrible quality, unfortunately) on tests in early 1942 of 45mm APCR with different core materials and different projectile design, but the same geometry for each core material (tungsten carbide or high-hardness steel). It turned out that I was wrong: steel cores demonstrated much worse armor penetration and were never mass-produced - they were even banned from further testing.
A projectile with a more massive core had higher armor penetration but worse accuracy and was rejected.
When German shells were fired from a Soviet 37mm anti-tank gun in 1941, the armor penetration was superior not only to the original Soviet shells but also to that of Soviet 45mm shells.

Armor penetration is a subject so complex that even different modern computer models can't always agree on results. A projectile moving at 2500f/s and penetrating 4-in of armor all happens in 13 MICRO-seconds (.00013 sec, or thereabouts.) Macroscopic (Newtonian) things happening in this short amount of time can give results that are almost impossible to predict with certainty. There's shock waves bouncing around, melting of both the projectile and target due to kinetic energy transforming into to thermal engergy, unequal forces on the projectile and target, etc. There are numerous "formulas" for amor penetration that can be modeled (PRODAS, Thompson, Lambert-Zukas, etc.) and all their outputs will vary with different materials on both the target and projectile. The best you can do is predicting "roughly" what will happen, or should happen. Google a copy of AD1045347 (PDF, 2018) for information on the WWII 76mm Sherman tank gun vs Tiger/Panther using modern "computer models" to get an idea for how complex this subject is. Hat's off to you, though. Your studying this subject is highly admirable, and "you will never have to prove your courage to me in any other way." Post anything interesting you find (or calculate.)

 

[Shortround6]

The basic equations are just that, basic. They use a lot of assumptions and constants.
But trying to chase down the minor variations can drive you crazy.

For basic penetration you have to figure out where the material that was occupying the hole goes. Like expanding a cylindrical hole sideways using hydrostatic pressure vs the projectile pushing out a cylindrical plug in the presence of constant shear stress at the surface of the plug. Now just figuring that out at different velocities, different thicknesses, different armor compositions and different shapes and compositions of penetrator gets well above my paygrade, assuming you can even find a lot the information needed.
Hardness of armor and the penetrator are just minor details. Tensile strength and yield strength and shear strength and so on.
And what is are the measurements of the armor (or projectile) in it's final state. How much (or little) work hardening or heat treatment or annealing or other factors that change it from the base stock (raw material) specifications and what was the quality of the work done?

the vast majority of projectile vs armor match ups are going to fall into expected ranges. Not to say that some are not out of the expected ranges but those should be examined close as to why or if they are at the end of a range of expected results. Also actual impact velocities are rarely given which means people are often working with inaccurate data (guessing).

 

[Jabberwocky]

Also, HESH did double duty as a HE round and was used as such - eliminating the need to carry an additional type of ammunition.

The countries that adopted HEAT rounds either carried dedicated HE rounds in addition to the APDS and HEAT - or developed HEAT/MP rounds to be used as a bit sub-par HEAT and HE.

UK Challenger crews in Iraq and Canadian Leopard 1 tank crews in Afghanistan also speak appreciatively of HESH as a anti-structure and/or breaching round. Lots of rounds put into buildings and walls to support infantry breaching and/or suppress fire. Plus the bigger bang vs HEAT helped. A105mm HESH round has somewhere around 2.7 to 2.9kg of Comp B, vs about 0.9 to 1.1kg in a HEAT round.

Infantry was also appreciative. HESH rounds apparently don't send as many fragments backwards and out to the sides as HEAT rounds do, so they could be closer to a target structure or have less danger when a tank was firing close.

"The 105 mm HESH round is the bread-and-butter munition for the tank squadron in theatre: each round knocks five-by-five meter holes into grape-drying huts and we have found it highly effective against dismounts at ranges of 150 to 3800 meters."

Source: Major Trevor Cadieu, 'Canadian Armour in Afghanistan' Canadian Army Journal Vol. 10.4 (Winter 2008), 5-25

https://www.canada.ca/content/dam/dnd-mdn/army/lineofsight/articleimages/2021/10/D12-11-10-4E-p5-25.pdf

 

[yulzari]

There were many reasons the British loved HESH which extend beyond its spalling effect upon frontal armour. It simplified the suite of ammunition on board ie if you don't need APDS then HESH will for the bill. A HESH round carried in the gun can do a lot of damage whilst the APDS round is reloaded thereafter and HESH at extreme ranges drops in from on high and meets less armour when it meets the roof or engine deck. When hit by 120mm HESH round (I am personally more familiar with Wombat use than tank) most of the things needed for the enemy to fight their tank fall off or break even if it has not done assorted unpleasantries to the squishy things inside the armoured box.

 

[Shortround6]

A lot of people failed to take into account that knocking out tanks was a two step process.

Step 1. Penetrate the armor.
Step 2. Damage something behind the armor (crew, ammo, drive train, fuel, etc)

Really small anti-tank rounds often needed multiple hits even if they "pierced" the armor.
HEAT (shaped charge) projectiles need a certain amount of over penetration to have good chance of killing/injuring the crew or damaging internals.
Thick armor actually helps damage things inside the tank once penetration ahs been achieved.

A 7.9mm Anti-tank rifle penetrating 10mm armor means a small projectile (or pieces of) and a small amount of displaced armor flying around the inside of the tank.
A 75mm projectile penetrating a Sherman tank front slope means a lot of metal flying around inside the tank. The Original projectile and/or pieces plus all the material that came out of the hole.

HESH bypasses the 1st step and goes to the 2nd step, several pounds of metal flying around inside the tank.

 

[tomo pauk]

In the hope that loads of the captured French 25mm ATGs will be of any use in future, Germans were developing the APCR shot for it. At 220g, it was a lot lighter and, as expected, much faster than the 'normal' AP shots for that gun, expected penetration at 60 deg (30 deg per NATO speke) was supposed to be 50mm at 100m (German data for that guns shows 35mm penetration under the same conditions).

Click for hi-res.

 

[tomo pauk]

Among the smaller HEAT shells fired from the 'normal' guns, seems like that Japanese were among the best when it was about squeezing the most from a very light gun (~200 kg):

Type 92, 70mm Battalion Gun -80mn (3.15 in) armor at angle of 60 degrees, and 100mm (3.93 in) armor at 90 degrees. (from here)

Perhaps the penetration was helped by the small rotation of the shell due to the low MV?
The ~4.5kg HE shell was fired at some 200 m/s, while the HEAT shell weighted 2.8 kg - making perhaps 250+ ms from the muzzle? A more ambitious gun, with a longer barrel, would've halved the difference vs. the 520 m/s MV of the PAW 600, while still being light enough - talk 300 kg ballpark?

 

[Shortround6]

It could be error.
Getting 100mm of penetration out of a 70mm diameter war head/shell is defiantly in the upper reaches of shaped charge penetration in WW II.
And 70mm is being generous.

This a pretty good shape for a shaped charge as many others were too short, not giving the charge enough time (distance) to form up properly.
Now if you add 50% to the muzzle velocity you also increase the spin rate by 50%.
US 75mm pack howitzer fired a HEAT shell at 305m/s. instead of the 381m/s it could fire the standard HE shell, perhaps due to spin and perhaps the slower speed allowed more time for the fuse to function and the jet to form as the nose crumpled.
US shell was good for 3 1/2 (89mm) of penetration.
Same shell may have been used in the 75mm recoilless gun (different driving band?)

The PAW 600 is generally rated as having a 750m effective range, which is still a sort of arched trajectory.
A gun that split the difference in velocities might have an effective range of 600 meters or a bit less.

A

 

[tomo pauk]

It could be error.
Getting 100mm of penetration out of a 70mm diameter war head/shell is defiantly in the upper reaches of shaped charge penetration in WW II.
And 70mm is being generous.

It might indeed be an error.
What was probably more important that the 'book values' was how it dealt with real tanks. Seems like that Sherman was within the abilities, per Wikipedia:
U.S. tests in the Philippines with captured 70 mm HEAT rounds proved capable of puncturing the turret of a M4A3 Sherman tank and was rated at an excess of 70 mm of armor penetration. [8]​

Drawing shows a void between the shell and the propellant - sorta very low-tech high/low pressure system? I'f I'm reading that right, the weight of the propellant was 1.6 oz, or about 45 g; the max propellant weight went to 138 g for the 70mm gun. So despite the lower weight of the HEAT shell, it will be launched at pretty low MVs.

The PAW 600 is generally rated as having a 750m effective range, which is still a sort of arched trajectory.
A gun that split the difference in velocities might have an effective range of 600 meters or a bit less.

Looking at the kwk 37, that fired the HEAT shell at even lower MVs, that one was good for 66% chance to hit (a tank-sized target?) at 1000m, and 99% at 500m. FWIW

 

[bf109xxl]

A gun that split the difference in velocities might have an effective range of 600 meters or a bit less.

I'm just wondering how this howitzer with weak ballistics (almost mortar-like) could hit a moving tank at a distance of more than 50m?