Alternative light and anti-tank guns, 1935-45

[peceed]

Penetration goes up with the square of the speed. 10% more veleocity means 21% more penetration in theory.

According to the de Marre formula, it is more like V^1.4283, or Ek^0.714.

The HEAT round at 4.54kg was fired at 450m/s.
The Pak 40 fired a very similar projectile at 450m/s also.
The 8cm PAW fired a 2.70kg HEAT projectile at 520m/s.

The muzzle velocity of 450 m/s was a limitation caused by rotation.
The PAW600 was limited by the muzzle energy resulting from the gun's mass.

US had tested the T45, a HVAP for the M3 75mm gun.
8.4 lbs/3.8kg projectile at 2870fps/870m/s
116mm penetration at 500 yard with 30 degree plate

Interesting - 1.4MJ of muzzle energy. The cartridge probably had a very shallow bullet seating, therefore a larger amount of powder.

A few posts ago in this thread, I've suggested that the small gas divert tube is added to the small AT gun so the recoil is lowered, since part of the high-speed gasses is pushed backwards. That again means that the whole gun can be lighter due to the lower stress exerted on the weapon. Sorta 10% recoiless gun.

A very stupid idea - introducing the main utility disadvantage of a recoilless weapon (backblast) without tactical advantages (weapon with minimal mass). In addition, it causes a rather significant loss of muzzle energy.

RT-20 was supposedly doing 850 m/s, despite the short barrel and the divertion of small % of the gasses.

Do you believe in fairy tales?
Using the same cartridges as the M55, the rifle achieves the same muzzle velocity with a barrel that is half as long with a gas bleed?
2/3 of the length of the Polsten barrel...

 

[tomo pauk]

A very stupid idea

I wish you all the best.

 

[peceed]

I wish you all the best.

It's nothing personal. Stupid ideas deserve an honest assessment. The lack of feedback deprives you of information when you should have thought twice, making it impossible to improve.
Crazy ideas might work, stupid ones don't.

BTW, flooding the forum with ill-considered ideas is a form of trolling. If you like the game, fine, but expect direct criticism.

 

[peceed]

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

But this does not work with any form of composite or space armor. Actual penetration is no greater than ~1.25x caliber.

The higher values mentioned, such as 400mm for 125mm guns, are the equivalent for heavily sloped monolithic steel armor - slope has minimal effect on hesh penetration in absolute terms.

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

The best candidate is the 37mm SA 18 for obvious reasons, highly developed (by WWII standards) variants could achieve penetration of up to 50mm.
Earlier development of HEAT ammunition would be an excellent alternative to the SA 38, radically improving French AT capabilities.

The pre-war development of shaped charges fired from low-velocity guns would have hampered the development of tank armour, favouring more light and fast machines.

 

[Shortround6]

Are we looking at history sort of how it actually happened or are we getting into the "what if" if they knew in 1938 what they knew in 1943-44 or a 1938-1948 time shift?

Military shaped charges in several countries came about, at least according to most popular history's, when different military's were offered "NEW, Powerful Secret Explosives"
by inventor XX. There seem to have been at least 2 teams running around at about the same time offering pretty much the same spiel, including test demonstrations.
In the stories an astute observer (or more than one) recognized the effect they were witnessing as the old Munro effect from 1888, although the idea was used earlier but trying to use the idea with black powder meant it wasn't very effective.
At any rate the general narrative is that the astute observers either declined the offer or recommended their governments either decline the offered "secret explosive" or offer much less than the asking price. Armies started working on reproducing the observed effects from the demonstrations at their own testing facilities and thus the shaped charge entered service.
Sort of.
British No. 68 Rifle Grenade which entered service in Nov 1940 (?)

When the picture was taken (Home Guard in 1942) the British army was recommending best distance was 50-70 yds and best use was at the rear of a tank after it had passed by.
The 2.5 in diameter bomb was supposed to go through 2in of armor if it hit at a good angle.
There were several reasons for this

Like not enough stand off, a less than optimum cavity diameter to projectile diameter and a less than optimal distribution of the explosive.
The Explosive in the rear corner of the 'cup' doesn't do much for the shaped charge.

The Germans are reported to have used shaped charges by the assault engineers attacking the Belgian fortress but these were large demolition charges and while effective, they may have been skipped over by the anti-tank crowd. Germans later (?) used large shaped charges held by magnets to attack tanks.

This came in different sizes but the 3kg version is considered to have been good for penetrating 140mm of armor (?).
Not a good result for the size of the cone and explosive weight to be copied by a gun designer.
Some the other early German tries did not give great results. First German 75mm shaped charge projectile was good for around 40mm of penetration ?
More in next post.

 

[Shortround6]

German 10.5cm shaped charge shells.

The later, longer shells were credited with penetrating about 100mm of armor.
First version was good for ???
Short stand off and nose fuse arrange (even push rod?) disrupts the formation of piercing jet.

British screwed their anti-tank guns with cheap ammo but the APCBC shot dates back to WW I, over 20 years, although that was for the large guns and not small guns but it is pretty much a question of scale and not coming up with new designs, like the Germans were trying to do with the 10.5cm howitzer shells.
Looking at the illustration, which version do the Germans (or anybody else) use in 1940-41?
And these a long way from what armies did in the late 40s and 1950s in terms of design so trying to apply post WW II penetration values to pre or early war shells needs time travel.

 

[tomo pauk]

Are we looking at history sort of how it actually happened or are we getting into the "what if" if they knew in 1938 what they knew in 1943-44 or a 1938-1948 time shift?

As with all what-if topics, we look at the historical stuff to arrive at the ballpark of what might've been done. A part of this what-if are also the infantry guns. They can get a new lease of life once the HEAT ammo is introduced.

Some of the short 75-76mm guns were doing pretty well wrt. armor penetration with APHE shells, like the French or the German 75mm guns in the late-1939 tanks. These guns would've be doing well as the base for the towed AT guns, while also very useful to deal with infantry and the light field fortifications.
Advantage of the sizable APHE shell will be that the enemy tank will be a mess even with one hit, something that was not true for the 25-40mm ammo doing the same.

 

[Shortround6]

As with all what-if topics, we look at the historical stuff to arrive at the ballpark of what might've been done. A part of this what-if are also the infantry guns. They can get a new lease of life once the HEAT ammo is introduced.

Some of the short 75-76mm guns were doing pretty well wrt. armor penetration with APHE shells, like the French or the German 75mm guns in the late-1939 tanks. These guns would've be doing well as the base for the towed AT guns, while also very useful to deal with infantry and the light field fortifications.
Advantage of the sizable APHE shell will be that the enemy tank will be a mess even with one hit, something that was not true for the 25-40mm ammo doing the same.

In 1939, except for the British, the Armies had AT guns that went from 310-450 kg in weight and 37mm to 47mm bore size except for the Czech 4.7cm AT gun at 570kg.
The British were really the odd man out with 40mm 2pdr at 814kg but almost 1/2 (?) of that is that Rolls-Royce carriage. The gun tube and breech block was only 131kg.
Simple split trail with 60 degree traverse would have put the 2pdr down in the 450-500kg weight range.

In just 5-6 years countries were looking at 114-128mm AT guns that even towed, out weighed some early war tanks.

The Germans were large fans of infantry guns. So were the soviets

But the thing weighed about 760-780kg and you are going to need some well fed troops to move it very far without horses.
Using early shaped charges in early "infantry" guns of smaller size wasn't going to get you much.
The French infantry gun were left over 37mm.
The Italians were already using the 47mm DP AT/Infantry gun
The Japanese were using two different 37mm guns, the 70mm and were giving old 75mm mountain guns to regiments more as regimental artillery than front line guns but the Japanese were clever and also short of equipment. But if you need AT ammo for this thing

You have made a huge error in getting your troops in area where your troops are facing tanks of any sort.
The US got into and out of infantry guns twice?
For the most part the US kept artillery to the rear and relied on radios for HE support.
The closest the US got to infantry guns in most units were the 37mm AT guns.
The British stayed out of the infantry gun business except for a few 3.7in Howitzers and the 95mm fiasco. Guns designed and built and when presented to the infantry were basically told "You silly buggers, why did you do that, we didn't ask for them, we don't want them and we won't use them".
So basically you have the Germans with the the 7.5cm IG 18 and what ever the Germans scrounged up to make up for shortages after the war started and the Soviets.

Trying to combine the two categories of guns is attractive but may lead to compromises to either role. If you have superior forces you can use HE ammo from your AT guns to supplement other weapons. But at times you want your AT guns in forward positions to stay hidden waiting for the enemy tanks. Which means you need additional guns for HE/smoke support. If you need light weapons due to lack of mechanized transport (or lack of horses) do you want to speed weight on angle mounts for AT guns?

 

[tomo pauk]

The Germans were large fans of infantry guns. So were the soviets
But the thing weighed about 760-780kg and you are going to need some well fed troops to move it very far without horses.

The US got into and out of infantry guns twice?
For the most part the US kept artillery to the rear and relied on radios for HE support.

Some of these pieces seem to be over-weight for what they were offering. Like the Soviet M1927, at about 750 kg in it's lightest iteration while offering the same MV of the US pack howitzer that went as low as 570 kg.
German mountain gun M36 was at 750 kg indeed, but it offered another 100 m/s over these two guns as well as the split carriage. The muzzle brake was certainly a factor wrt. the weight savings, so there is no reson why the other guns of that category cannot have the muzzle brake, too, in odred to save some weight. The M36 was also offering 90 m/s over the pak 50 for the full-weight shells, that, at 1100 kg, was 450 kg heavier.

Trying to combine the two categories of guns is attractive but may lead to compromises to either role. If you have superior forces you can use HE ammo from your AT guns to supplement other weapons. But at times you want your AT guns in forward positions to stay hidden waiting for the enemy tanks. Which means you need additional guns for HE/smoke support. If you need light weapons due to lack of mechanized transport (or lack of horses) do you want to speed weight on angle mounts for AT guns?

If the army of the day forgoes the light AT gun and makes additional infantry guns (say, 2 per each 3 AT guns that are not made), while introducing AP ammo for them, they might end up with a formidable AT defense.
British and French might even get 1:1, infantry gun vs. their heavy AT gun - the 47mm APX was above 1000 kg

In 1939, except for the British, the Armies had AT guns that went from 310-450 kg in weight and 37mm to 47mm bore size except for the Czech 4.7cm AT gun at 570kg.
The British were really the odd man out with 40mm 2pdr at 814kg but almost 1/2 (?) of that is that Rolls-Royce carriage. The gun tube and breech block was only 131kg.
Simple split trail with 60 degree traverse would have put the 2pdr down in the 450-500kg weight range.

British buying the licence for the 47mm Bohler would've been even better.

 

[Shortround6]

German mountain gun M36 was at 750 kg indeed, but it offered another 100 m/s over these two guns as well as the split carriage. The muzzle brake was certainly a factor wrt. the weight savings, so there is no reson why the other guns of that category cannot have the muzzle brake, too, in odred to save some weight.

German M36 was a little too light. Ok in the howitzer role not so good in direct fire. Granted the lighter shaped charge projectile was fired with charge 4 but using charge 5 with the standard HE shell meant you could not fire at less than 15 degrees elevation as the gun bounced around too much. The gun pivoted around trail spaded and picked the wheels up of the ground. We are also getting to travel problems. Like designing for horse traction or for 30kph travel or for 50-60kph travel.

British buying the licence for the 47mm Bohler would've been even better.

Not really, just stop being idiots and load 40mm Bofors shells into the 2pdr cases, issue 2pdr HE ammo from the start.
Not great but 2.3 times the amount of TNT in an American 37mm AT gun shell and nobody was leaving them back at base.
Decide what you want the gun to do, then do it and issue at least at least useful ammo accordingly.
British 2pdr with the first AP shot (not shell) will penetrate at about 500 yds the same armor at 30 degrees as the Italian gun does at 0 degrees.
With either the HV shot (extra powder) or the ABCBC shot it will go through about the same armor at 1000 yds as the Italian gun will do at 550yds.
In fact the Italian gun was rated at 43mm at 0 degrees at 550yds while the 2pdr APCBC was rated at 35mm at 30 degrees at 2000yds. This unfortunately assume the British give it a sight that allows for hitting at 2000yds even allowing for 3rd or 4th round hit.

There was nothing wrong with the 2pdr gun itself. Keep the gun, get a simpler/lighter carriage. Load up some HE shells and newer than 1904 AP projectiles and kick the Italians out of NA.
Fooling around with HEAT rounds for 3.7in howitzers or for tank 3in howitzers on ground carriages or other fancy things (and requiring more man power, British infantry battalion was lucky they had enough manpower for pair of 3in mortars, Where was the man power and transport for the infantry guns supposed to come from?)

 

[tomo pauk]

Not really, just stop being idiots and load 40mm Bofors shells into the 2pdr cases, issue 2pdr HE ammo from the start.
Not great but 2.3 times the amount of TNT in an American 37mm AT gun shell and nobody was leaving them back at base.
Decide what you want the gun to do, then do it and issue at least at least useful ammo accordingly.

Heavy weight of the gun was a problem. This is why I've suggested that a more sensible weapon is made. Heavy weight meant that the gun was transfered to the artillery units, and away from the infantry units(1), the intended costumer.
Also a lot cheaper and faster to make(2).
1 + 2 meant that British were lacking the modern AT guns in 1940, and that they were using a lot of the borrowed 25mm guns.

British 2pdr with the first AP shot (not shell) will penetrate at about 500 yds the same armor at 30 degrees as the Italian gun does at 0 degrees.
With either the HV shot (extra powder) or the ABCBC shot it will go through about the same armor at 1000 yds as the Italian gun will do at 550yds.
In fact the Italian gun was rated at 43mm at 0 degrees at 550yds while the 2pdr APCBC was rated at 35mm at 30 degrees at 2000yds. This unfortunately assume the British give it a sight that allows for hitting at 2000yds even allowing for 3rd or 4th round hit.

Whatever the tank was that the 2pdr was piercing in 1939-41, the Bohler was too. And whatever the better ammo the 2pdr can get, so can the Bohler. British can even arrange the deal so it to fires their 3pdr Hotchkiss ammo.
Money & time saved for not going with the unicorn undercarriage and a newly-designed gun can be used on making the naval 6pdr guns also for the Army needs.

British wasted too much time, resources and money to reinvent the wheel when it is about the AT/tank guns.

 

[tomo pauk]

Not really, just stop being idiots and load 40mm Bofors shells into the 2pdr cases, issue 2pdr HE ammo from the start.
Not great but 2.3 times the amount of TNT in an American 37mm AT gun shell and nobody was leaving them back at base.

To return to this.
The 47mm Bohler fired, at least in Italian service, a 2.37kg heavy HE shell. No 40mm shells will ever come in close.

 

[Shortround6]

Heavy weight of the gun was a problem. This is why I've suggested that a more sensible weapon is made. Heavy weight meant that the gun was transfered to the artillery units, and away from the infantry units(1), the intended costumer.
Also a lot cheaper and faster to make(2).
1 + 2 meant that British were lacking the modern AT guns in 1940, and that they were using a lot of the borrowed 25mm guns.

Not sure that the British infantry was ever the customer.
A lot depends on the armies doctrine. Towed AT guns were never platoon or company weapons.
The British in 1938-1940 had lightly equipped battalions.
the Battalion had two 3in mortars total as I have said.
There were no Vickers guns, at all.
They had 50 Bren guns, 22 .55 AT rifles (if they were up to strength) and 12 2in mortars. Everything else was rifles and pistols.
Transport was 35 bicycles, 14 motorcycles, one 4 passenger car, nine 8cwt trucks, 32-33 15cwt trucks and 12-13 30cwt trucks and 10 Bren carriers.
They had gained men and rifles from 1938 to April of 1940 but little else.
British use of 25mm guns in 1940 was also a part nod to interchangeability with the French, not sure the British got a good bargain. The flimsy French gun carriages broke when towing forcing the adoption of carrying portee. Not a good solution when you are short of trucks to begin with. Not sure what the French got in exchange?
It was after France when the AA platoon was up graded to twin Bren guns in each truck and they up graded the mortar platoon to 6 mortars and 7 Bren carriers (now mortar carriers) instead of trucks.

It is not until late 1941 or early 42 that the 2pdrs arrive in the infantry battalion. But total manpower falls by 6 men. You have to redo British army doctrine, tactics, units assignements and so on to get AT guns into the Battalion's hands in 1939-40.

Whatever the tank was that the 2pdr was piercing in 1939-41, the Bohler was too. And whatever the better ammo the 2pdr can get, so can the Bohler. British can even arrange the deal so it to fires their 3pdr Hotchkiss ammo.
Money & time saved for not going with the unicorn undercarriage and a newly-designed gun can be used on making the naval 6pdr guns also for the Army needs.

British wasted too much time, resources and money to reinvent the wheel when it is about the AT/tank guns.

Not sure where this is coming from. The Bohler is light gun and there is no magic, the gun in action was 277kg which is much lighter than the German 37mm AT gun? The HE round was fired at 250m/s.
Types of AP round are related to impact velocity, You could make a 47mm APCBC round for the Bohler but since the Bohler isn't going to hit the target at a velocity that is going to break up the uncapped shot it is just an unneeded expense/complication. British 25pdr fired a 20lb AP shot and using either APC or APCPC wasn't going to chance the performance much. US 75mm tank ammo was about the same velocity and had both uncapped and APCBC shells (In the US APCBC is called APC, they never made a capped projectile without the ballistic cap. The British made all three types). In the Sherman 75s you can see a difference and it shows best against the the two types of armor. The high velocity 2pder needed capped shot to perform well.
Saving money for the army to build coastal defense weapons is not a good trade.

To return to this.
The 47mm Bohler fired, at least in Italian service, a 2.37kg heavy HE shell. No 40mm shells will ever come in close.

The Bohler fired a much smaller cartridge case the old British 3pdr ammo and there were several different types of 3pdr ammo, a lot of it dates from the 1880s.
Information on the 1920s-early 30s 3pdr guns using some British tanks is hard to get. The Vickers are considerably more powerful than the old Hotchkiss guns but both are very overweight and neither has a recoil system as built. The British medium tanks of the 1920/30s seem to have used a new barrel and recoil system but chambered (?) for the old Hotchkiss ammo and the old ballistics. Which is why the British replaced them with the 2pd. A 3lb shot at 563m/s was not going to do the job. The 3pdr in the Medium MK II was rated at about 27-28mm at 30 degrees at 500yds. Again, these are NOT old naval guns.


The 40mm HE shell will not come close to the Italian 47mm but as I noted, it is way better than the American 37mm and it is way better than the German 37mm that was used as a support weapon in quite a number of German 1/2 tracks. Also the 37mm guns used in French tanks and the 37mm guns used in Japanese light tanks.

The British were making 2pdr pom-pom shells and were gearing up to make 40mm Bofors shells, waiting until late 1942 to put an HE shell into a 2pdr case is one of the great British mysteries.

 

[tomo pauk]

Not sure where this is coming from.

What is a problem wrt. what I've wrote about the Bohler?

Saving money for the army to build coastal defense weapons is not a good trade.

How much of imagination is required to imagine the RN's 6pdr on a split carriage, or as a tank gun?

 

[Shortround6]

How much of imagination is required to imagine the RN's 6pdr on a split carriage, or as a tank gun?

If the goal is to reduce the capabilities of the British army then we don't need much imagination.
I am sorry Tomo but this idea of using 10-40 year old barrels is not a good one, either in emergencies or as patterns for new manufacture.

The 6pdr 7cwt gun was very good gun and it weighed, as indicated around 727lbs to 783lbs depending on exact barrel model/mark, length of barrel and counter weight or muzzle brake.

The Breechloading navy guns start with the 1883 6pdr Hotchkiss 8 cwt. Which weighed about 849lbs for a slightly shorter tube. It also had a velocity of 1765fpm/538ms and since the gun had been designed for black powder and even newer ones built in the 1890s were built to use about the same ammo using hotter ammo was risky. The old full length 6pdr was good for about 397,000 joules of energy and the cut down guns used in the WW I tanks were good for 230,000 Joules. There is at least one picture of an old WW I tank gun on a towed, wheeled mounting (Home Guard?) but that does not mean it was a good idea for a service weapon.
Now when they cut the barrels off in WW I they became the 6pdr Hotchkiss 6 cwt


The coast defense 6pdr 10cwt that you linked to is just that, a 1060lb barrel and breech or an extra 300lbs for the crew to move around if we try to use it as an ersatz AT gun. It also, as originally loaded fired a 2.83kg HE shell at 718ms for 731,000 Joules of energy. The cartridge case was bit longer but a bit skinner than the 6pdr 7cwt gun. The AT gun could fire an over 3kg projectile at 790ms even in the short barreled guns. With different weight shot and different velocities things mixed up the the AT gun was operating in an area of around 950,000 to 1 million Joules of energy with the corresponding armor penetration.

And there were not that many of the 6pdr 10cwt guns to swipe.

There was a 6pdr 6 cwt but that is the experimental high velocity AT gun that was not adopted. Also used it's own cartridge case.

Trying to use unorthodox ammo (HEAT or SABOT) rounds to try to resurrect these old guns may be a bigger engineering feat than simply designing a gun and ammo to do what you want.
The British did use some of the old guns as anti-invasion armament around the time of Dunkirk and after.

 

[tomo pauk]

If the goal is to reduce the capabilities of the British army then we don't need much imagination.
I am sorry Tomo but this idea of using 10-40 year old barrels is not a good one, either in emergencies or as patterns for new manufacture.

Despite me linking to a specific 6pdr, you pull out of a hat the other guns that nobody suggested.
Man.

The coast defense 6pdr 10cwt that you linked to is just that, a 1060lb barrel and breech or an extra 300lbs for the crew to move around if we try to use it as an ersatz AT gun. It also, as originally loaded fired a 2.83kg HE shell at 718ms for 731,000 Joules of energy. The cartridge case was bit longer but a bit skinner than the 6pdr 7cwt gun. The AT gun could fire an over 3kg projectile at 790ms even in the short barreled guns. With different weight shot and different velocities things mixed up the the AT gun was operating in an area of around 950,000 to 1 million Joules of energy with the corresponding armor penetration.

Timing beats the capability. Same when we talk how the P-39, that is available now, is beating the turboed P-39 that might be available two years in the future. Or that a Spitfire available now beats the Whirlwind or the Typhoon. Or a P-40 available now that beats the P-47. Or a P-51 that beast the all-new P-51H.
This is not to say that better stuff has no place in the planing and realization.

The 6pdr 10cwt gun as an AT gun and as a tank gun can offer the AP performance better than the best light At guns of the day, like eg. the Czech and French 47mm guns, as well as the future short 5cm, and can be had months before 1939, and can offer a lot between 1939 and 1942 (even later with the more modern ammo).
Start designing the 75mm HV by 1940. Both as a tank gun and as an anti-tank gun, and flood the battlefield with these by winter of 1942/43.

And there were not that many of the 6pdr 10cwt guns to swipe.

Hence my prior suggestion to avoid the 2pdr, make a simpler and cheaper light AT gun instead, and use the time and resources saved to increase the production of the 10cwt.

Trying to use unorthodox ammo (HEAT or SABOT) rounds to try to resurrect these old guns may be a bigger engineering feat than simply designing a gun and ammo to do what you want.

Usually that was not the case.
Once can also make the APCR shot early on.

 

[Shortround6]

The 6pdr 10cwt gun as an AT gun and as a tank gun can offer the AP performance better than the best light At guns of the day, like eg. the Czech and French 47mm guns, as well as the future short 5cm, and can be had months before 1939, and can offer a lot between 1939 and 1942 (even later with the more modern ammo).
Start designing the 75mm HV by 1940. Both as a tank gun and as an anti-tank gun, and flood the battlefield with these by winter of 1942/43.

The barrel and breech of the 6pdr 10cwt gun weighed few dozen pounds more than an American 75mm 1917A4 barrel and Breech. It weighed just about the same as an American 105 howitzer barrel and breech. It weighed 60lbs more than 25pdr barrel and Breech. Granted you don't need quite as much chassis but this is not going to be a "light" anti-tank gun. It weighed more than a complete ready to tow American 37mm AT gun.
There are few reasons for the weight, one of which you may be able to solve in this adaptation. The 6pdr 10cwt gun used a freakishly short recoil stroke, quite possibly to help speed up the rate of fire. Does make it easier to put in a tank turret.

You can turn down the outside of the barrel and build a new recoil system.
Going to capped or ABCBC is new to some guns but it is old (Mid/late WW I) technology. You can use APCR shot but since you are starting with a medium velocity gun you don't get quite the benefit. Trying to use HEAT in a 57mm is problem. The British tried HEAT in the 25pdr but the spin, as with other guns, degraded the effect and the British went back to old, tried a true solid shot with and extra powder charge and quickly a muzzle brake.
BTW the 6pdr AT gun was designed in 1938 and test fired in 1939.

Hence my prior suggestion to avoid the 2pdr, make a simpler and cheaper light AT gun instead, and use the time and resources saved to increase the production of the 10cwt.

The 2pdr gun itself was cheap and light, what was not cheap and light was the 360 degree mount.
And the 10cwt is not the direction you want to go anyway. The chamber was about 3/4 the size of the later AT gun.
The 10cwt was put into production in 1934, the 2pdr was approved in 1936.

 

[tomo pauk]

The barrel and breech of the 6pdr 10cwt gun weighed few dozen pounds more than an American 75mm 1917A4 barrel and Breech. It weighed just about the same as an American 105 howitzer barrel and breech. It weighed 60lbs more than 25pdr barrel and Breech. Granted you don't need quite as much chassis but this is not going to be a "light" anti-tank gun. It weighed more than a complete ready to tow American 37mm AT gun.

My intention is not to have the 6pdr to be a light gun.
The elevating part of the gun (barrel, breech, recoil system, cradle) weight was 481 kg. There is a lot of headroom until we reach 1000 kg for the complete towed AT gun.

There are few reasons for the weight, one of which you may be able to solve in this adaptation. The 6pdr 10cwt gun used a freakishly short recoil stroke, quite possibly to help speed up the rate of fire. Does make it easier to put in a tank turret.

Ability to be easily installed in the tank turret is a major boon. Not just for the British, many times it was very hard to substantially up-gun a tank.
The AT version might possibly be better served with the recoil system and cradle that allow for a greater recoil stroke, however, thus reducing the peak recoil forces.

TW the 6pdr AT gun was designed in 1938 and test fired in 1939.
The 10cwt was put into production in 1934, the 2pdr was approved in 1936.

The 10cwt had a lot going on for it.

The 2pdr gun itself was cheap and light, what was not cheap and light was the 360 degree mount.

Unfortunately, the AT units might have a wee bit of a problem if the mount is not available for a towed gun they just received

 

[Admiral Beez]

It would be interesting to see the British Army's Ordnance QF 2-pounder combined with the RN's QF 2-pounder naval gun.

You're in your Carro Armato M13/40 or Type 95 Ha-Go light tank and come face to face with this beast - firing, albeit low velocity AP at high rpm. Of course we need to get this onto a truck or carriage.

Our how about a single 40mm autocannon, like the Rolls-Royce 40 mm cannon?

 

[tomo pauk]

Going to capped or ABCBC is new to some guns but it is old (Mid/late WW I) technology. You can use APCR shot but since you are starting with a medium velocity gun you don't get quite the benefit.

To take a peek on this.
Looking at the Soviet and US/French really medium-velocity 76-75mm guns, they all gained the improved penetration when the 'cored' ammo was used. The HVAP ammo offered more than 50% better AP performance than the APC ammo on the US gun. The Soviet 'arrowhead' projectile was better AP perfromer than the initial BR-350A ammo by some 10-20%.
We can also take a look at the Kwk 38, a.k.a. the short 5cm gun, used on a number of the Pz-IIIs in 1941 and 42. It started out with a lower velocity shot (under 700 m/s), that improved greatly with the APCR shot. Penetration between 1000m and 100m distance went up by the 20 to 70% interval (= greater increase closer to the gun).
The Kwk/StuK 40 L43 was also no great shakes wrt. the muzzle vlocity (full-weight projectile at 740 m/s, vs. ~720 for the 10cwt), and still the APCR brought the similar %-age jump in AP abilities as it was doing with the Kwk 38.

Advantage the British have vs. any Axis power is that the former don't need to skimp on tungsten.