Alternative light and anti-tank guns, 1935-45 (7 Viewers)

[tomo pauk]

Penetration data for the different German guns & ammo.
Note that data for some interesting ammo types are missing, like for the Pzgr.40 fired from the Kwk 40, Pak 40 and the Czech 47mm. Also note that the Czech 47mm listed there is about 50-100% better than a 37mm, and in the ballpark with the long 5cm. Data for the pak 36(r) firing the Pzgr.40 is very suspicious - it was probably for the FK 36(r), ie. the one not out-bored to fire the more powerful ammo?
Note that the Pak 41 is in the ballpark with the Panther's gun against the targets tilted by 30 deg, but weaker against the targets at 0 deg. Both of them can deal with the KV-1 by at least 1500m, and vs. a T-34 by at least 2000m. Granted, Panther's gun can do it with the Pzgr.39.

table

Penetration table for the Soviet 85mm gun, for different ammo types: table

 

[z42]

The theory is good (mostly) the execution is the problem.
If the APDS does not separate cleanly and consistently accuracy turns to crap. It doesn't matter how good the penetration is if the majority of rounds fired do not hit the target.

Agreed, I even explicitly mentioned that in the first sentence of my post: "...had APDS been developed into a more mature state in the run up to WWII...". An APDS design is indeed pointless if it can't hit the proverbial barn from the inside.

We can play with the math a bit more and see where we wind up for Joules per sq cm of plate area to find out what is needed for steel cores to work, assuming there is no problem with the steel cores shattering.
The French were trying to improve some pretty low performance guns, tying to improve even 600-700ms guns gets a lot harder because you are trading away the weight per unit of frontal area for velocity.
Shot size..............weight............................grams per unit of frontal area.
40mm......................1088g.................................86.62
50mm......................2050.................................102.13
57mm......................2720.................................106.66
75mm.....................6800...................................154

A the same velocities it is the weight per unit of frontal area that is important until we get into exact heat treatments/hardness and failures of material.

Let's play at bit more. So assuming we start with a 75mm gun that can shoot a traditional full-bore AP(C(BC)) shell at 600 m/s (keeping nice round numbers to keep the math simpler). Let's use the 6.8kg weight you quote, which should be in the ballpark for a WWII era APCBC shell. Now if we instead want to shoot a subcaliber round at 900m/s, keeping the kinetic energy constant assuming that's roughly proportional to recoil, barrel pressuer etc., we need the weight of the subcaliber round to be 4/9th of the weight of the full bore shell, that is 3.0kg.

To determine the required diameter of the 3.0kg shell, let's assume it's the same shape and density as the full bore shell. This gives us the diameter of the subcaliber shell as the diameter of the full-caliber shell times the cube root of the relative masses. Thus 57mm.

Note there is some inaccuracy here. The recoil is not exactly proportional to the kinetic energy. And the mass of the sabots has not been taken into account. And further the APDS shot is denser as it doesn't have a cavity filled with low density HE. And probably the shape of the APDS projectile can be optimized somewhat as it doesn't have to take into account need for driving bands etc. But let's assume we're in the ballpark. That is, a 6.8 kg 75mm shell at 600 m/s vs. a 3.0kg 57mm shell at 900 m/s.

Now to determine the penetration. If we use the Thompson F-formula, if we rearrange it a little bit we can see that the penetration T is proportional to the kinetic energy divided by the frontal area, times some unit conversion factors, obliquity factors and some semi-empirical correction factors (the "F-factor" which includes shell shape, material etc. etc.). So in both cases we have the same kinetic energy (at the muzzle), but the subcaliber shell has much less frontal area. And thus the penetration will be higher, by a factor of (75/57)^2 = 1.7.

Now if we switch to tungsten, the big advantage here is that we can get the same KE in a narrower shell, thus increasing the penetration. Let's use tungsten semicarbide, which AFAIU was used during WWII, with a density of 17.15g/cm^3, vs. 7.85g/cm^3 for steel. Doing the same calculation as above, but taking into account the difference in density, we get d2 = d1 * cbrt(m2/m1 * rho1/rho2) = 44mm. Plugging that into the penetration calculation, we get compared to the full-bore shell a penetration a factor of (75/44)^2 = 2.9. So quite a big difference indeed. And of course, tungsten carbide doesn't have the same problem of shattering as steel, so no need to limit ourselves to a MV of 900m/s. We could increase the MV and reduce the diameter and get even better results. Left as an exercise for the reader.

And further, as you say, the narrower tungsten penetrator will also lose velocity slower. Assuming the rate of velocity loss is proportional to the KE/frontal area similar to penetration, (57/44)^2 = 1.7. So the tungsten penetrator can fly a distance of 1.7 times further than the steel penetrator for the same loss of velocity.

So yes, clearly tungsten is superior. But per the above, steel APDS is still better than traditional full-bore APCBC.

 

[Shortround6]

You are close to the Historic US 75mm T45 round tested (issued?) for the M3 gun in the Sherman tank.
actual MV of standard M61 round (14.96lbs) 619m/s
actual MV of the T45 round (8.4lbs) 867m/s.
This was an APCR round so includes the sabot, adjust as you see fit.

https://www.theshermantank.com/wp-content/uploads/75mm-M3-spec-booklet-MK-VI.pdf

Seems like no two tests even agree on the penetration of the standard AP rounds.

But firing a 6lb (?) penetrator (steel) out of 75mm gun at 860-870m/s doesn't seem to over any advantage over a 57mm 6pdr gun firing a 6pdr (?) projectile at about the same speed.

We are back to arguing about giving field guns special AT rounds and misusing the field guns in the interest of commonalty of production. But field guns are larger and heavier than AT guns so cost and production times need careful consideration.

As for target effect, even a 75mm APDS with steel penetrator is not going to be any better at distance than an American/British 6pdr with standard shot.

Results for the T45 shot kind of show why it wasn't adopted in large numbers. With a shortage Tungsten Carbide and with the 75mm gun even with APCR shot having a minimal chance of killing a Panther from the front but being able to use full bore steel shot out to `1500-2000yds on the sides/rear it was decided to use the Tungsten Carbide in the 3in/76mm HAVP to give those guns a better chance in frontal attacks.

 

[ThomasP]

For anyone interested in the esoterica.

The Tungsten-Carbide (WC) alloys used in WWII were not the same as modern Tungsten Heavy Alloys (WHA), and the WC densities were significantly below the 17.15 of the (heaviest) modern WHA used in today's penetrators.

Nation____________Density____Chemical Composition
WWII German_____~15.36_____Cu 5.5-6.1%, Ni 3.0-2.5%, WC & W2C 91.5-91.4%
WWII US/UK______~14.11_____Co 13%, WC 87%

NOTE
1. The reason for the significantly greater density of the German TC cores is partly due to the use use of the different binders and/or % of binder materials, partly due to the use of a greater % of W2C (density of 16.47) vs WC (density of 11.21), and partly due to the larger grain size of the TC-Co structures.
2. All of the German TC cores were ~15.36 density, except for penetrator cores of the 7.92mm AP round, which may have ventured into the WHA range. If the numbers I have are correct, the density was 15.88 for the most common Tungsten alloy types in the 7.92mm rounds. Unfortunately I do not have very good data on these, and the design variations and manufacturer tolerances re the shape and size of the core lends to inaccuracy in any calculations.
3. The US & UK did experiment with TC alloys using less Cobalt (Carboloy 44A & 779 in particular), and with WHA alloys (Elkonite et-al in particular), towards the end of the war. I have not found records indicating any of the US or UK heavier alloy projectiles entered service during the war.

Material_____ Density
Copper_______ 8.96
Nickel_________8.91
Cobalt________ 8.90
WC__________11.21 pure, as used by the US & UK in WWII
W2C_________16.47 pure
WC/W2C_____14.17 as used by the Germans in WWII

 

[tomo pauk]

Yet another table dealing about the AP performance, this time the German 75mm stuff.
Some things might be interesting, like the suggested usage of the 75mm HEAT ammo on the Pak 41 (perhaps just once per gun ), or the AP capabilities of the Pak 41 soft-steel shot, the PzGr. 41 (W). That is actually not bad - it can hurt the T-34 or a Sherman despite the material of the shot. It is also interesting that the siliar shot was to be made for the full-bore 75mm KwK 40. Almost 5.9 millions of the HE ammo available for the 'French 75' is also of note.



Unfortunately, there is no penetration data for the very interesting Patr. 41(St.K.) - the small APCBC shot to be fired from the Pak 41. The most similar shot, at least by the time that shot is flying, is/was the Soviet 57mm APCBC, a 3.19 kg shot fired at about 1000 m/s. Good for about 90mm at 100m, and 60-74mm at 1000m, all for 30 deg slope NATO; note that Soviet AP ammo have had problems due to the inconsistency of quality between the batches. Here is the German penetration chart:



So at least two conclusions by your's truly: Germans should've made a more powerful cannon instead of the 5cm pak, and the pak 41 would've been very useful with the 'proper' steel-cored AP ammo.

 

[tomo pauk]

To show just how much the 5cm pak and it's tank-going counterpart were under-powered, I've bashed together some crude graphs for the APCBC shots. Original is same as above. The blue and magenta lines are for the worst-case and best-case 6pdr APCBC shots, respectively (data from here). Red is for the 5 cm. All for 30 deg slope NATO.
I didn't bothered with the short 5cm.
It looks to me as if the Germans just gave up on improving the APCBC shot for the 5 cm, but then again the Allied guns used much heavier propellant charges.
The good penetration abilities of the 6pdr were no secret, even without use of tungsten-tipped shots - these abilities would've meant a lot to any Axis power, being shot with the tungsten. Even going with conservative estimates - in-between the worst- and best-case of the 6pdr APCBC depicted by the thick green line - the T-34 would've been a fair game even at 1500m, and the KV's of 1941 at 1000m?

 

[tomo pauk]

A 'quazi-APCR' shot for the 10.5cm howitzer. Uses the Pzgr.39 from the 7.5cm guns as parts donor:

 

[Elan Vital]

A 'quazi-APCR' shot for the 10.5cm howitzer. Uses the Pzgr.39 from the 7.5cm guns as parts donor:

View attachment 860607

I notice the Germans have the same naming quirks as the French in that "sabot" is used even for fixed carriers.

 

[tomo pauk]

The ordnance of the single-shot 3.7cm (German) and 4cm (Czech) AA guns would've been doing okay as the anti-tank guns.
The 4cm type was operationally used just by the interwar Yugoslavia, and was firing a powerful shell: 0.95 to 1 kg at 950-945 m/s (ie. in-between the pre- and post-war 40mm Bofors AA types). Or, some 20% more powerful than the initial 2pdr ammo, or still about 10% more powerful than the mid-war 2pdr ammo. Have it fire a good ammo, and it should be getting excellent results against any German stuff before they start making the 80mm armor front for their AFVs.
With an APCR shot - Tigers and Panters are the fair game?
Similar with the German gun, possibly made instead of the 4.2mm squeeze bore gun? Say, the Kriegsmarine sees the wrong of their ways by 1940, and barters the single-shot 37mm guns (both these acquired and these still under production) for something more useful. Army is delighted, since they can get double or triple the number of light AT guns vs. going with the 4.2 cm.

 

[tomo pauk]

I've probably suggested it earlier, but anyway: the 88L/56 as an anti-tank gun in a towed or self-propelled flavor. As a quick fix, installed on the 10.5cm howitzer mount; should be less of an awkward thing than the 88L/71. Yes, still very much a brute, but not the brute of the 17pdr, let alone of the pak 43 league; another advantage is that the 'baby 88' can be tested even before the war.
A more compact and light gun would've also been a better fit for something like the Geshutzwagen III/IV, that was a basis for the Nasshorn and Hummel.

A comment on how the 88mm can torn-off the turret of the T-34 or the Matilda II (engl. Pz.Mk.II) with a good hit with the HE shell, even at longer ranges with a sensitive fuse installed; also a note that the HE shell is not very accurate on the longer ranges:

 

[Elan Vital]

The key conclusions I made from this thread and research is that in many ways most of the guns one could think of in that time period were actually thought of (or even reached the project stage), which is why I and others in this thread often enumerated real projects and ideas.

Be it with:
- pre-existing cartridges and ballistics
- existing cartridges that are hot loaded, necked in/out, cut to a given volume
- cartridges and guns made to achieve the goal of existing cartridges, but smaller (76 M1 vs M7)
- completely new cartridges

Only so much new stuff can be done, and more often than not it will be redundant or will have to displace an existing gun.

 

[tomo pauk]

The key conclusions I made from this thread and research is that in many ways most of the guns one could think of in that time period were actually thought of (or even reached the project stage), which is why I and others in this thread often enumerated real projects and ideas.
Be it with:
- pre-existing cartridges and ballistics
- existing cartridges that are hot loaded, necked in/out, cut to a given volume
- cartridges and guns made to achieve the goal of existing cartridges, but smaller (76 M1 vs M7)
- completely new cartridges
Only so much new stuff can be done, and more often than not it will be redundant or will have to displace an existing gun.

There was a lot of duplication of effort and missed opportunities, too. Add some pie-in-the-sky ideas, like the small calibre squeeze bore guns despite having the opportunities to do the similar job with classic guns, and there is lot to comment upon, and indeed criticize the powers that were.

Germans: Along with the squeeze bore guns, there is the 5cm conundrum - reinvent the wheel with two new guns and two new ammo types, initially one as a tank guns and second as an AT gun, despite having the option to choose from the 5 and 5.2cm guns that are a known quantity even before Nazis came to power. And then they choose 5cm as a new calibre for the new gun (13mm 'away' from 37mm, and 25mm 'under' 75mm), instead of going to 55-60mm, with appropriate loads to get the best out of that. Such a gun would've been a good fit on the AFVs, too, and a real threat to the numerous Allied nedium tanks like the T-34, M3 and M4, Matilda II.
Not trying more with the 600-700m/s 75mm guns in the AT role before 1941 was a missed opportunity.
Insisting on towed 128mm and long 88mm AT guns, while skipping the more realistic 88L56, long 75m as well as the 105mm guns was a mistake IMO. Granted, having the heavy towed guns has it's disadvantages, but still.
Instead of the Pak 41, that used the addition to the barrel extension - why not make something that is a 55-ish calibre 75mm gun due to a full-bore extension? Hot load a bit the Pak or KwK or Flak 75mm ammo to ~3kg of propellant, and it is reasonably future-proof, does not badly need tungsten (but will make a good use of it if/when available), and it can fit on 20-25 ton AFVs, perhaps even on the turret of the Pz-IV. Basically the 'German 77mm HV', can be done in 1941/42 (design/production).
Mis-management with the captured guns and production lines was also a big mistake.

IMO - already getting rid of the squeeze bore guns while working on the more 'classic' guns, and having the Pak 38 to be a more 'serious' gun would've make the German gunners much more of a threat than they were historically so.

 

[Shortround6]

There was a lot of duplication of effort and missed opportunities, too. Add some pie-in-the-sky ideas, like the small calibre squeeze bore guns despite having the opportunities to do the similar job with classic guns, and there is lot to comment upon, and indeed criticize the powers that were.

This is quite true.
Some of the technical "solutions" were not really practical at the time. Tungsten carbide worked and worked well, problem was that nobody had very much of it. One book claims that many of the German tanks in Russia had 5 rounds or less in 1941. Which really calls into question the whole taper bore/tungsten carbide core weapons program from the start. If you can't supply the ammo in quantity why are you spending time designing/manufacturing the guns?
Even the US could not make tungsten cored ammo in large quantities (enough for more that 2-5 rounds per tank destroyer) in 1944. US and Britian could hope for increased supplies. The Germans could not.

Germans: Along with the squeeze bore guns, there is the 5cm conundrum - reinvent the wheel with two new guns and two new ammo types, initially one as a tank guns and second as an AT gun, despite having the option to choose from the 5 and 5.2cm guns that are a known quantity even before Nazis came to power. And then they choose 5cm as a new calibre for the new gun (13mm 'away' from 37mm, and 25mm 'under' 75mm), instead of going to 55-60mm, with appropriate loads to get the best out of that. Such a gun would've been a good fit on the AFVs, too, and a real threat to the numerous Allied nedium tanks like the T-34, M3 and M4, Matilda II.
Not trying more with the 600-700m/s 75mm guns in the AT role before 1941 was a missed opportunity.

The gun makers (companies) had a pretty good idea of what they could make using their machinery and using the materials of the day. 1935 offered large advances over 1915 let alone 1895-1905. The gun makers would base new designs off of old ones and try to incorporate new materials and manufacturing techniques. Most companies (at least large ones) were working on ballistics on test ranges. Getting somebody (government) to pay for lots of research was the hard part. Or to get the government to give realistic requirements. Pre WW II German 10.5cm howitzers had aluminum parts in the carriage to meet the weight requirements for towing (number of horses needed). That did not last long as they needed aluminum for aircraft.

As to caliber, the seemingly small jumps in size of the bore could mean large jumps it the weight of the gun/equipment. Basic gun design goes with the cube law. You can finesse it somewhat but basically the difference between a 5cm gun and 6cm gun is the difference between 125 (5 cubed) and 216 (6 cubed). This would assume same length barrels (in calibers) same internal pressures and other things being the same. This also applies to the mount/carriage/turret.
Modern (post WW I) barrel construction allowed for much lighter barrels than the barrels of the same performance built in the 1890s and 19. So we have to be careful comparing guns to make sure they are of the same design era. The US 76mm tank gun was a great example of modern (late 30s) steel manufacturing and modern propellent technology compared to early 1900s. Design goal was to get the same ballistics (or close) as the 3in 1903 coast defense gun (by way of the 1917 3in AA gun). They got the desired ballistic performance in much, much lighter barrel using a cartridge of less volume.
Even Henry Ford had been persuaded to give up on the 1908 model T in 1927 start making new cars and engines in the late 20s and 30s.
Tell the designers what you want and let them try to make it happen without being constrained by old guns/ammo in warehouses/stockpiles.
The German short 5cm tank gun was a mistake. The only 2 things it really had going for it over the long 5cm was that the crew was less likely to whack the barrel against an obstruction (tree, telegraph pole, building) than a longer barrel and less need for storage space for a given number of rounds. That barrel overhang was really important to a lot of countries, design teams in the 1930s. Seems to have disappeared fairly soon after the shooting started.
Of course, the whole 37mm in the MK III fiasco for compatible ammo was a mistake. Turret on the MK III was adaptable to larger guns. How much large is the question.

For some reason it seems that the tank designers could come up with new tanks faster than the gun designers could come up with new guns
By the time a new gun got into service there were new/larger tanks to shoot at. Some of this was not taking into account the actual time (issue of requirement to actual service use) of the tanks and guns in question and the appearance that the two different teams (Tank vs Anti-tank) weren't talking to each other even the same countries.

Insisting on towed 128mm and long 88mm AT guns, while skipping the more realistic 88L56, long 75m as well as the 105mm guns was a mistake IMO. Granted, having the heavy towed guns has it's disadvantages, but still.

Very true. They were not the only ones. The American and British monstrosities tend to be overlooked as they never got out of the proving grounds.
And the design requirements had changed. Instead of wanting small AT guns that could deal with 5-15 ton tanks of the 1930s many armies wanted AT guns that could deal with 60-100 ton (or more) tanks and now you had to come up with tow vehicles to match. A small truck was no longer good enough let alone horses.
British were not going to use a Bren carrier to tow a 17pdr.

Crusader hull/chassis. Granted the Allies had hundreds of old tank chassis that would still run. Moving 3 1/2 and larger AT guns with their crews/equipment and required ammo required as much thought and manufacturing as the guns themselves although often overlooked.
Standard German 3 ton 1/2 tracks with 4.2 liter 100hp engines are not going to cut it.

Some of the failed American projects even for the 76mm towed AT guns show so some of the problems. Attempts to keep the whole thing small/light lead to wheels being too small (poor towing) and the gun barrel too low causing the barrel to hit the ground while towing. Combat requirement for low silhouette conflicted with towing/transport requirement to get the guns to where they needed to be.

Germans knew they were working on the Maus tanks and were expecting the allies to do something similar (or at least something much bigger than Sherman and Cromwell) and with tungsten carbide off the table brute force was the easiest answer for penetration. American M-26 "heavies" when they got there, were not any better armored (if as well) as the Panthers of 1943.

nstead of the Pak 41, that used the addition to the barrel extension - why not make something that is a 55-ish calibre 75mm gun due to a full-bore extension?

Depends on what else was going on. Maybe you can machine the existing barrel to take a 12-15 caliber extension. But you need a cradle that can handle weight. Or stow the extension while towing and screw it on while emplacing?
And to get any worthwhile increase in velocity you need a bigger propelling charge. Which might require a new chamber and cartridge case. New cartridge case/chamber means you can't use the old ammo stockpiles any more. Or at least not as is. You can salvage the powder and projectiles for reuse.
A lot may depend on how much rework you want to do of existing guns or perhaps I have misunderstood and you are talking about a Pak 41 with a non-tapered barrel using full bore ammo. Some sources claim that some of the Pak 41 carriages were given Pak 40 barrels. Perhaps that is the best path.

 

[tomo pauk]

As to caliber, the seemingly small jumps in size of the bore could mean large jumps it the weight of the gun/equipment. Basic gun design goes with the cube law. You can finesse it somewhat but basically the difference between a 5cm gun and 6cm gun is the difference between 125 (5 cubed) and 216 (6 cubed). This would assume same length barrels (in calibers) same internal pressures and other things being the same. This also applies to the mount/carriage/turret.

The weight difference between a good 5cm and a good 5.7cm gun was not the difference between how many times 185 (= 5.7 cubed) can 'hold' 125s, ie. the 6pdr was not 50% heavier than the Pak 38, but some 10%. And still the 6pdr fired a far heavier projectile (talking just about the full-weight stuff), with the much better performance.
Germans have had the wherewithal to make something like the 60 cal version of the Soviet 57mm gun by the late 1930s, but that never happened.

Tell the designers what you want and let them try to make it happen without being constrained by old guns/ammo in warehouses/stockpiles.

I have no problem with that idea.
My take is that both things can be done: push the state of the art higher via asking more from the guns' and ammo designers and makers, and see how the existing stuff can be suitably modified to the new task. Having the plan B is and still was a prudent thing in the militaries.
Not trying to reinvent the wheel would've also been a good thing.

For some reason it seems that the tank designers could come up with new tanks faster than the gun designers could come up with new guns
By the time a new gun got into service there were new/larger tanks to shoot at. Some of this was not taking into account the actual time (issue of requirement to actual service use) of the tanks and guns in question and the appearance that the two different teams (Tank vs Anti-tank) weren't talking to each other even the same countries.

I'd say that both tank and guns' designers were always trying to up their game. Sometimes a promising tank or a gun was simply put aside, that sometimes had the unwanted consequences. Like not installing a more serious gun on the Stug-III before 1940 despite the obvious advantages, or the British army not wanting to have anything with the RN's 6pdr. But we've been over the British light guns' controversies too many times.
German 37mm was also a meh gun (and definitely over-produced), even when compared with other 37mm AT guns from the 2nd half of the 1930s. As above, German industry was more than capable to make something better, on time and on dime.

They were not the only ones. The American and British monstrosities tend to be overlooked as they never got out of the proving grounds.
And the design requirements had changed. Instead of wanting small AT guns that could deal with 5-15 ton tanks of the 1930s many armies wanted AT guns that could deal with 60-100 ton (or more) tanks and now you had to come up with tow vehicles to match. A small truck was no longer good enough let alone horses.
British were not going to use a Bren carrier to tow a 17pdr.
Crusader hull/chassis. Granted the Allies had hundreds of old tank chassis that would still run. Moving 3 1/2 and larger AT guns with their crews/equipment and required ammo required as much thought and manufacturing as the guns themselves although often overlooked.
Standard German 3 ton 1/2 tracks with 4.2 liter 100hp engines are not going to cut it.

Very true.
Perhaps an experiment of installing the 17pdr on the Crusader hulls would've produced a workable result? Best case in a light & open turret, like what the Achiles had? Or in a fixed mount, if the light turret does not fit?
Too bad the 77mm HV was not made before the 17pdr, not later.

Depends on what else was going on. Maybe you can machine the existing barrel to take a 12-15 caliber extension. But you need a cradle that can handle weight. Or stow the extension while towing and screw it on while emplacing?

I'd press on with the new barrel, and mod all the carriages or mounts to hold these barrels. Make the complete weapons with these properties by 1943, while phasing out the L43, 46 and 48 barrel versions.

A lot may depend on how much rework you want to do of existing guns or perhaps I have misunderstood and you are talking about a Pak 41 with a non-tapered barrel using full bore ammo. Some sources claim that some of the Pak 41 carriages were given Pak 40 barrels. Perhaps that is the best path.

The Littlejohn adapter was an attachment to an existing gun barrel. Similar procedure - attachment on a cylindrical barrel - was used to make the pak 41 barrel. My suggestion is along these lines, just that the attachment is of cylindrical shape, not conical.
Pak 40 barrels were 46 cal length, I'd suggest to go to around 55, together with the slight increase of the propellant charge to go with that.

 

[yulzari]

Perhaps an experiment of installing the 17pdr on the Crusader hulls would've produced a workable result? Best case in a light & open turret, like what the Achiles had? Or in a fixed mount, if the light turret does not fit?

The Crusader was out of production by that time being replaced by the Cromwell. That Cromwell, post war, was modified to carry the 20 Pounder in a light rotating turret. Even the 105mm L7 in one trialled case. There is nothing stopping the same being done in 1944 with the 17 Pounder. A Challenger done better.

 

[tomo pauk]

In the words of Oprah: you get the 77, you get the 77, everyone gets the 77mm HV.

1st, the British: As with other gun-making countries, such a gun was very much within the scope of the industry even before ww2. Realistically, it might've been introduced by early 1942? Advantages: a great AT gun even with ammo that is not fancy or new-tech, can be easy fit even on the 25pdr carriage, as well as on the halftracks. Possibly a good fit on the Churchill as-is? The British not-Stug, too - IOW a 20 ton AFV that can kill tanks without being too picky? Much easier to install on the Shermans, so possibly by the D-day most of the British Shermans have it as a business end.

Germans: Make it instead of the Pak and Kwk 41 (yes, there was such a thing mooted), and then press on by making it instead of the Pak and Kwk 40. Possibly getting about 100 mm at 30 deg at 1000 m (vs. the Pak 40 doing 88mm, and Kwk 42 doing 111mm); the 77mm HV was getting 110mm at 30 deg at 1000 yds against a homogeneous plate.

Americans: A bit better than the 76mm, handy against the better German tanks, like the Tiger and Panther.

Soviets: A much better gun than what they were installing on their tanks before the late 1943, as well as a much better AT gun than the field 76.2mm pieces.

Italians: A gun that their industry can make in better quantities than the 90mmm for the not-AA needs? Also a good fit for their Semoventes.