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?

 

[tomo pauk]

The rocket-assisted HEAT shell, fired from the modest guns (like the kwk 37/ pak 50), might've improved the odds of hitting a more demanding and a distant target. In the ex-Yu, the recoiles gun was firing the 'normal' HEAT shell at about 380 m/s, and had the point blank range of 530 m for a 3m high target. The rocket-assisted shell improved that by a good margin, for it the point blank range for a 3m target was 930m; for a 2m high target, it was 775 m/s.
Rocket motor was ignited at about 4m past the muzzle.
The old cartridge and shell in the left, the new on the right (click on it for the higher resolution):



We can recall that the RPG-7 uses the similar principle of a 'kick-out' propellant + rocket motor, with the later taking over once away from the shooter's face.

Obviously, the initial propellant charge on a normal cannon will be far lighter/smaller than what the recoiles gun ammo used. Germans did toyed with the rocket-assisted ammo for the 15cm howitzer, so it is not a really ground-breaking concept for them.
Concept would've also worked in the breech-loaded mortars, that the paw 600 was a version of.

 

[Shortround6]

In practice it often did NOT work as well as advertised.

and the low recoil AFV version.

Ammo

Now this pair of devices uses a smooth bore tube. It also has several problems. Getting the rocket motor to kick in in a uniform manner 10-20 meters from the muzzle was problem and this was in the 1960s and early 70s. This is a problem with ALL rocket assisted shells. How big is the problem depends on the degree of rocket boost, when the rocket boost occurs, the method of stabilization and the quality of manufacture. I may have ignored something.
This weapon uses flip out fin stabilization, which does work better (most of the time) than trying to use long skinny fins that do not exceed the gun tube diameter, and better than short stumpy fins that do not exceed the gun tube diameter.
However it also means that in the first few meters (depending on how fast the fins flip out) stabilization is a little lacking and the round may not be pointing exactly where you want it when the rocket motor kicks in. At which point it takes off in the new direction. Hopefully it is still on a tank size target at the desired range.
This is in calm weather or facing into the wind or with a direct tail wind. Cross winds can introduce another problem with accuracy. This thing stabilizes like the arrow from a bow. Except with a rocket motor in the tail, the rocket can weather cock into the wind and with the thrust of the rocket motor the round will actually miss toward the direction the wind is coming from, not away from it.
Granted a WW II version may use a bit more gun and bit less rocket which might reduce this tendency a bit.
It is possible to use a rifled tube and fins and this, while more expensive, may keep the round steadier in the first few dozen meters while speed builds up. May also mean you can use shorter fins?
A lot depends on just how tricky you want to be.
The Belgians used a 90mm rifled low pressure gun (the Mecar) in the early 50s and sold some of them to Switzerland.

Which is kinda/sorta a modernized PAW 600.

 

[tomo pauk]

Granted a WW II version may use a bit more gun and bit less rocket which might reduce this tendency a bit.
It is possible to use a rifled tube and fins and this, while more expensive, may keep the round steadier in the first few dozen meters while speed builds up. May also mean you can use shorter fins?
A lot depends on just how tricky you want to be.

I'd suggest not being too tricky
Something like the Japanese 70mm gun or the plethora of the other light/infantry guns used rifled barrels, where the disadvantage of the lower MV was probably an advantage wrt. the armor penetration since the rotation was also slower. Shell can indeed be more of a cannon shell, rather than a rocket - something like this to illustrate the point (but with the HEAT payload, not HE as depicted):



Historically, this was the ammo for the ww1-era German 7.58cm mortar, where the propellant was located within the shell. Here, the bottom part of the HEAT shell should contain the rocket motor (doh) with a delayed ignition.
Same/similar principle was used on the Japanese 40mm airborne cannon and the Soviet 40mm UGL.
The ex-Yu RCL gained perhaps another 300-350 m/s to the MV of 380 m/s (judging by the incraese of the point blank range) by using a substantial rocket motor. A less powerful motor should be tailored for adding about 200+ m/s to the muzzle velocity?

 

[Shortround6]

Some information on the Mecar 90/28 light gun.

Difference in rate of fire between the towed gun and the ADV gun may be the difference between 3-4 men operating in the open and 2 men inside a somewhat cramped turret.


The gun works by using a very light projectile in 90mm bore which gives fair velocity over short range.
It offers low recoil, low blast/signature (compared to normal 75-90mm guns) and no back blast like a recoilless gun.
The tube is rifled which adds to expense.
Now things get real confusing as Mecar offered a longer, heavier, higher velocity 90mm gun and ammo. The Cockrill company offered both short and long 90mm guns and a French company also offered a short/light 90mm gun for armored cars which used similar but not interchangeable ammo. The French gun is a smooth bore.
I was in error, the Swiss guns do not use the Mecar ammo but may use a similar design concept.

In the Soviet bloc, the Soviets and many of the old east bloc states used the 73mm guns/ammo discribed earlier.
There were also several 82mm weapons. Yugoslavia had one recoilless rifle, the Soviets had another and the Czechs had two. One much smaller/lighter than the others, the Tarasnice 21 of the early 50s. But I believe these are all recoilless guns but some (or all?) did wind up with rocket boosted shells.

 

[Shortround6]

I would note that the effective range listed in the above posts may be from company advertising/testing and not customer testing
Also to be noted is that shaped charge design made huge stride post WW II and in the Early 1950s. Expecting anywhere near that level of penetration with similar size (diameter) projectiles in WW II is unrealistic.

I would also note that the use of surplus 6pdr carriages for the towed gun may have been expedient/cheap but the carriage was probably overkill for the gun.

 

[tomo pauk]

Now things get real confusing as Mecar offered a longer, heavier, higher velocity 90mm gun and ammo. The Cockrill company offered both short and long 90mm guns and a French company also offered a short/light 90mm gun for armored cars which used similar but not interchangeable ammo. The French gun is a smooth bore.

Thank you for this - I was aware of the 'Cockelrill' gun and Mecar rifle grenades, but this is new to me

From what I've gathered so far, the list can be made like this:
- Mecar 90: heaviest and most expensive gun, most accurate one, too; cheap ammo is a plus, too
- paw 600: lighter and less expensive gun, not as accurate, also used cheap ammo
- Soviet 73mm: still less expensive and lighter (at least the ordnance part of it), probably not too accurate due to the working principle of the RAP shell; most expensive ammo if one wants high MV and long reach
- Japanese 70mm: a true bargain, used cheap ammo, small effective range

This is without the RCLs taken into the account.

How low might one go and still have a satisfying light AT gun that uses HEAT? Even the rifle grenades of under 65mm were still good for penetration of 3in/76mm of armor (60mm Bazooka that used the warhead of the M10 rifle grenade did this; German 61mm r-g was supposed to do 130mm - caution advised for this value?). So basically a 60mm breech-loading mortar can still hurt a ww2 tank badly, it is bound to be much more accurate and of a longer range than the hand-held weapons, and will weight under 200 kg.
On the opposite end, a RAP version of the 80-90mm HEAT shell fired from something like the Mecar 90 would've probably be doing about 800 m/s (so hitting a tank reliably over 1 km), while penetrating well over 200mm of armor (the 89mm super Bazooka was suppsoed to do 280mm).

 

[marathag]

How low might one go and still have a satisfying light AT gun that uses HEAT?

Or the early HESH the Italians used, EP 'Effetto Pronto'

A HEAT round that frequently acted like a squash head detonation against the plate from the base fuze being slow

A factoid I had from -somewhere- over at AH?

In March 1942, in the Saunnu (Cyrenaica) area, the 12th Autoraggruppamento (the Italian "experimental" unit in North Africa)
put the EP rounds for the WWI vintage 75/27 field gun and 100/17 howitzer to the test. Two 75mm and two 100mm EP rounds
were shot at a captured Crusader MkVI tank at a distance of 550 yards. The 75mm rounds easily smashed and penetrated the side and frontal armor plates, with plate shrivelling (presumably due to the "boiling jet"effect). The 100mm rounds disintegrated the frontal armor and popped
the turret out of the tank.

A 75mm shell hitting the 2 joint of two plates 30mm and 20mm thick respectively on the front of the hull opened the metal and curled back the metal tearing the upper inclined plate making a hole 30 x 50cm.
A 100mm shell hitting the front of the turret made from 2 x 20mm plates (40mm total) tore the face off the turret
A second shot at the turret tore it off leaving it on the ground