Getting the best mileage from the squeeze-bore guns? (1 Viewer)

For the French, I already mentionned the 37/28 and 75/65 mm guns with conical muzzle devices. Sadly I've not found any documentation on their performance or the base guns.
Obviously by 1940 the squeezebores had strong competition from Brandt APDS and LCFA APCR.

The 37mm casemate Mle 1934 (and a related towed version that started development in 1940) with a Littlejohn-style design would have been analogous to the 2pdr Littlejohn.
The 47mm SA37/39 would be a good candidate.

The tank guns (37mm SA38 and 47mm SA35) may yield useful results with similar devices.

I discussed the actual squeezebore gun projects (28/20 Larsen-Gerlich-APX L824) and the Tulle arsenal (MAT) 20/16 and 20/14mm weapon in Secret Projects Forum:

The latter was basically a response to the problem of arming the infantry at even lower levels and even closer to the first line than the 25mm SA 37. It's an intermediate between AT rifles and the 25mm gun, but it's half the weight of the Fallschirmjäger version of the German 28/20 and has a 10-round magazine with semi and automatic modes to alleviate the issue of limited behind-armor effects for small caliber weapons.
The French 28/20 (similar weight class and origin to the German gun) was deemed too weak and it was suggested to have a weapon with a final diameter of 23mm, though I don't know if it keeps the original caliber of 28mm or something larger.
In general the squeezebore concept was suggested for application to larger calibers to obtain lighter guns for a given power level, like the Germans, but I'm not aware of any official projects.

The big enabler for the French down the line would be tungsten cores, as they had presently been trying to find better steel grades and core geometries. The use of steel meant that the 28/20 was superior against certain targets compared to the 25mm, but worse against other targets, so the squeezebore concept wasn't yet a straight upgrade.

Ironically enough, the French 75 would've been a better fit for a Marder-style tank buster than it were either pak 40 or pak 36(r), for the simple reasons of the gun being smaller and lighter, while firing the much more compact ammo. Stick the adapter on it, and it is at least equal to the Soviet F34 gun firing the APCR shot.
For the kicks and giggles - make the airborne cousin of the 75, like the Americans did with the M5 cannon for the B-25s. Would've probably looked good on any 2-engined aircraft.

Elan Vital said:

The big enabler for the French down the line would be tungsten cores, as they had presently been trying to find better steel grades and core geometries.

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There was an idea from 1943 that uranium might've been useful for the cores of the APCR ammo. I'm not sure that anything was actually done about it.



('Stuka' here means 'sturmkanone', ie. a cannons on the Stugs and the like)
Unlike tungsten, uranium - it's ore - was something that could be mined in Germany and Czechoslovakia.

tomo pauk said:

There was an idea from 1943 that uranium might've been useful for the cores of the APCR ammo. I'm not sure that anything was actually done about it.

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('Stuka' here means 'sturmkanone', ie. a cannons on the Stugs and the like)
Unlike tungsten, uranium - it's ore - was something that could be mined in Germany and Czechoslovakia.

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I suppose the problem with that is that there was very little demand for uranium before the advent of nuclear weapons and power. How quickly can you scale up mining and processing of a new material? 1943 at least is too late for Germany?

z42 said:

I suppose the problem with that is that there was very little demand for uranium before the advent of nuclear weapons and power. How quickly can you scale up mining and processing of a new material? 1943 at least is too late for Germany?

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Seems like another idea that came too late, indeed. Uranium ore was contained in the ores mined already in 19th century in Germany and Czechia, and indeed uranium was a known and unwanted product (link). If there is approval for the idea already in September of 1943, arriving at useful quantities might've happen, with the early testing in the mean time with whatever uranium can be scrounged from the German civilian institutions? Possible initail manufacture and use by the time of D-day?
Too many uncertainties, even with Germans not bothering to make the depleted uranium.

Seems like the uranium from Congo was up for grabs by 1937; granted, by 1943, it might as well be on the moon as far as the Germans are concerned, not just because the Americans swiped it up

tomo pauk said:

even with Germans not bothering to make the depleted uranium.

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Hmm, without an enrichment program for weapons or power, there's no depleted uranium either. If you want uranium just for AP, it makes no difference whether it's natural or depleted. DU is used because it's a cheap byproduct of enrichment, not because it has any particularly desirable property that natural uranium lacks.

Metallic Uranium (ie where the fissionable isotopes have not been refined out) and DU have the same basic density and the same mechanical properties when alloyed with other metals. The only real difference is in the higher amount (~40%) of dangerous radiation emitted by the non-depleted Uranium metal. But even the higher amount of radiation is somewhat negligible due to the very small percentage (0.73%, ie less than 1%) of fissionable isotopes found in uranium ores (including pitchblende, which was available and was the source of German Uranium in WWII). The German Uranium ores available were primarily in the Ore Mountains region, south of Chemnitz and Gera.

Post-war, under the Soviets, over 220,000 tons of Uranium ore were mined from this area.

see "Wismut (company) - Wikipedia"

A story about the people and squeeze-bore guns in Czechoslovakia, link being posted at another forum.
(easy to translate by your browser)

Adopting surface (ground or sea) AA guns to aircraft use gets difficult. Usually due to weight and size.
Weight and size limit change with time. A 1939 gun/aircraft combination is going to be different than a 1943 gun/aircraft combination. Of course 1939 tanks are a lot smaller/thinner.

French didn't really need a 25mm airborne anti-tank gun. Squeeze bore or otherwise. Weight was about double that of a 20mm Hispano. Not what the French need with all of those low powered engines. The French did not have air superiority like the Germans had in some areas of Russia that allowed slow, heavily loaded AT aircraft.
The 20mm Hispano was very close to the 20x138 ammo used by the Germans, Italians, Finns, Swiss and Poles in a Varity of guns including large anti-tank rifles and vehicle mounted guns (like Panzer IIs).

Don't fix what is not broken.

The 25mm Hotchkiss AA gun was also known for vibration which is usually sort of code for excessive recoil or perhaps better stated, the moving parts of the gun stop rather violently at each end of the travel. Not what you want in an aircraft gun both for accuracy and weight needed to mount the gun in the airplane without damaging the aircraft.

A 37mm automatic for the Japanese; the Ho 204 seems to fit the bill.
It shows up late, it is about as powerful as the US 37mm. It gets the extra velocity by using a much lighter shell. Perhaps with taper bore it would be useful against M3-M5 Light tanks in late 1944 or in 1945. Trying to use such a gun against Shermans does not stand a good chance of success and trying to use twin engine Japanese aircraft as tank busters given the level of American fighter protection is not going to go well. Just give the pilots single engine planes and have them crash into the tanks.

Americans adopt the 37mm AA gun for this purpose. The A-20 should've been able to hold a pair of these no problems.
Problems are many. While the 37mm AA gun used the same basic cartridge case as the 37mm AT gun ( changed the rim a bit) it did not use the same loadings (projectiles and powder charges). And trying to get automatic guns to work with different power cartridges gets tricky. Perhaps extending feed system to hold more ammo is not a big problem. Gun is about 88% as powerful as the German 37mm AA guns.

The 40mm Bofors.
Great gun. About 440kg for the barrel and breech, at about 85% more powerful than the US 37mm AA it has to be. At 64% more power than a British 2pdr Vickers S gun getting off fast repeat shots is going to be difficult.

Germans 'mechanize' the Navy's 37mm AA gun, and stick the adapter on the muzzle.
An auto-loader that allows for 50-60rpm or a true automatic gun that fires at 180-240rpm?

The whole flying AT gun was a mistake. Actual numbers of tanks destroyed was way less the propaganda claims. Planes trying to shoot tanks with AT guns are not bombing/strafing accompanying infantry/artillery/supply vehicles.
The tanks may have been most visible aspect of an attack/offensive but they needed the supporting elements.

Shortround6 said:

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Silly from me to believe that you will find benefits in any suggestion put forward.

A good 20mm AP round of some type could have been developed by the French for their 20mm HS aircraft guns. Possibly an extremely good AP round.

The British standard 20mm AP for most(?) of the war was the AP Mk II. It could reliably penetrate 36mm/31mm of typical German tank armour, at 0°/20° from normal, at 400 yds, when fired from an aircraft with a forward velocity of 238 mph (ie at Hurricane Mk IIC max speed on the deck at 2850 rpm and +9 lb boost ). The AP Mk III would in theory (I am not sure if it entered service or was used to any extent if it did) have been even more capable, with a penetration of 51mm/44mm when fired under the same circumstances at the AP Mk II. I believe this is enough to deal with the side, rear, and top armour on German early-war tanks up through the PzKw IV? While the British 20mm AP rounds were not crude, they were not in any way exotic.

What could the French have developed with their ideas/knowledge of HVAP and APDS?

ThomasP said:

A good 20mm AP round of some type could have been developed by the French for their 20mm HS aircraft guns. Possibly an extremely good AP round.

The British standard 20mm AP for most(?) of the war was the AP Mk II. It could reliably penetrate 36mm/31mm of typical German tank armour, at 0°/20° from normal, at 400 yds, when fired from an aircraft with a forward velocity of 238 mph (ie at Hurricane Mk IIC max speed on the deck at 2850 rpm and +9 lb boost ). The AP Mk III would in theory (I am not sure if it entered service or was used to any extent if it did) have been even more capable, with a penetration of 51mm/44mm when fired under the same circumstances at the AP Mk II. While the British 20mm AP rounds were not crude, they were not in any way exotic.

What could the French have done with their ideas/knowledge of HVAP and APDS?

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There were French Hispano and Brandt AP rounds (at least tested). Steel and tungsten carbide cores.

Did you happen to run across any projectile specifications, penetration values, or range/velocity tables?

tomo pauk said:

Silly from me to believe that you will find benefits in any suggestion put forward.

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I like suggestions that actually solve problems.
Looking at suggestions and trying to figure out why they wouldn't work puts us on the path to finding things that would work.

We do have the advantage of the retrospectoscope (hind sight).
Many people in the 1920s and 30s often did not look at what they actually needed.
They looked around, saw what their enemies (and allies) were doing, and sometimes just copied them even if they didn't understand quite why. Sometimes they thought the other guys knew something they didn't and didn't want to be left behind.
One thing when you are building 20 tons tanks. When you build 3-8000ton war ships just because your opponent build something maybe a bit more critical thinking is called for.

A lot of times to get a good benefit out of something several other things have to done/changed at the same time.

A lot of people during WW II were looking for "magic bullets" to defeat tanks. They didn't like the idea of just needing larger (heavier/more expensive ) guns to do it although they spent a lot of time/effort on these more conventional solutions.
Sometimes the "magic bullet" worked, like the shaped charge, but it took until after WW II to really get it up to snuff, like getting good fuses, figuring out a good shape for the inside of the cone, and figuring out how to get the needed stand off distance.
The Cored Shot was another "magic bullet" that worked even better than early shaped charges. But you need certain raw materials, You also need a lot testing and you have to follow some of stand ballistics laws.

And this is just to get the "magic bullet" to just penetrate like you want.
We haven't asked at what range or ranges?
If we want long range what does each "magic bullet" need/require to get hits at long range?
Are there any problems with getting hits at long range (accuracy of gun/ammo or accuracy of gun sights/laying system)

And then we still have not addressed the rate of fire or rate of engagement.
Or survivability after firing the first shot.
Recoil-less rifles were all the rage for 20-30 years. They were cheap, light and very mobile, if you weren't carrying very many rounds, or expecting the gun/s to last very long (a dozen shots?) before getting destroyed by return fire. Firing 1 to 2 rounds and then running away on fast vehicles was the common solution but requires terrain and a tactical situation that allows for defense in depth.

Shortround6 said:

I like suggestions that actually solve problems.
Looking at suggestions and trying to figure out why they wouldn't work puts us on the path to finding things that would work.

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This is certainly how you see it.
If you were to say something like this:
"Okay, so this suggestion has:
- possible benefits: x,y,z
- likely shortcomings: p, q, r"
...then I'd agree. But listing only shortcomings, and the benefits once in a blue moon gets old after some time.

ThomasP said:

A good 20mm AP round of some type could have been developed by the French for their 20mm HS aircraft guns. Possibly an extremely good AP round.

The British standard 20mm AP for most(?) of the war was the AP Mk II. It could reliably penetrate 36mm/31mm of typical German tank armour, at 0°/20° from normal, at 400 yds, when fired from an aircraft with a forward velocity of 238 mph (ie at Hurricane Mk IIC max speed on the deck at 2850 rpm and +9 lb boost ). The AP Mk III would in theory (I am not sure if it entered service or was used to any extent if it did) have been even more capable, with a penetration of 51mm/44mm when fired under the same circumstances at the AP Mk II. I believe this is enough to deal with the side, rear, and top armour on German early-war tanks up through the PzKw IV? While the British 20mm AP rounds were not crude, they were not in any way exotic.

What could the French have developed with their ideas/knowledge of HVAP and APDS?

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You could design/build more advance ammunition.

Now the question is what do you gain? At what distance can the aircraft expect to be able to hit the tank? And even a hit rate of 2 out 20 rounds fired or even 2 out of 30 may be be perfectly acceptable. Killing or wounding 1-2 crewmen may take the tank out of action for several hours?
HVAP may very well give you the increase penetration you want at the distances you want to shoot tanks at.
But steel cored HVAP may not. It may give better penetration at 200yds and less advantage as the range opens up. At what distance does the AT aircraft (Hurricane or other) have to stop shooting and pull up?
APDS offers better penetration than standard ammo at all ranges but the difference actually gets better at longer ranges.
But if you can't hit at long range (Hurricane trying to shoot tank at 1200yds?) what are you gaining?
And making a 12-13mm hole through the armor instead of a 20mm hole may not inflict the damage you want.

And it is best to pick one type of ammo and stick with it simplify aiming and tactics.

Some of the German small APCR ammo (37mm and under) performed real well at 100-200yds, not so good at 400-600 and worse than the standard AP shot at much over 600yds.
There is a cross over of the 50mm ammo too but at somewhat longer ranges and the 75mm doesn't cross over until around 1500-2000yds. This tracks pretty well with ballistics. Larger size ammo of any type retains velocity better. Changing type/style of projectile of the same size also affects things.
The squeeze bore stuff was trying to get high velocity and have a streamline shape doing it (and had a good sectional density) for long range performance. It succeeded at doing that but now you have to figure out it really gives you what you want at the distances you are trying to shoot at even if you can solve the materials problems and the barrel wear problems and the lack of effective HE problem.

tomo pauk said:

This is certainly how you see it.
If you were to say something like this:
"Okay, so this suggestion has:
- possible benefits: x,y,z
- likely shortcomings: p, q, r"
...then I'd agree. But listing only shortcomings, and the benefits once in a blue moon gets old after some time.

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Sticking the tape bore guns there are benefits
Higher velocity means.....
Better penetration, much better.
Flatter trajectory for easier hitting at longer ranges/shorter time of flight.
After that I start running out of benefits.
There are a lot of shortcomings. Some of high importance and some of low importance.
The high velocity benefit was certainly attractive and lured in many people. But they rarely overcame the shortcomings. Certainly not very many of them.

I have started looking at the soviet 45mm M42 AT gun as sort of a quick (or not so quick) alternative to the German 42/28mm gun. Not all sources agree with each other.
Unless sources are wrong the two guns were very close in weight, at least in action.
So we have two guns/weapons of fairly equal size/mobility and somewhat similar role. A 625-650kg towed AT gun.
The German gun is way ahead in armor penetration. But is it ahead enough when trying to deal with KV tanks ?
The German gun is easier to hit with at longer ranges (750meters and above?) but at 750meters and above the penetration has dropped to around 70-53mm depending on range and angle of impact so trying to shoot T-34s at over 1000 meters may not be a good idea. So the long range advantage is becoming less important (unless you want to shoot at recon vehicles).
Neither is trying to shoot T-34s with a captured 45mm M42 at long range

The German 42/28 has a truly crappy HE round 280 grams vs 2140 grams. The soviet gun sometimes has smoke round listed but even true, how many were built/issued is subject to question as is how effective a 45mm smoke shell is. What may have been more common (although still scarce) is a cannister round (137 balls).
Both guns have limited sights which somewhat limits long range use with any type of ammo.

What is sort of interesting is that Soviets got a claimed 74mm of penetration at 500m at zero degrees using an APCR projectile against the claimed 87mm at 500meters at 0 degrees for the 42/28 gun. Yes this is picking the best result for my argument.
Is the extra 13mm (17%) of penetration worth it?

A little more context. At 1000 meters the 42/28mm can go through 53mm at 30 degrees. A British 2pdr using APCBC can go through 47mm at 900 meters at 30 degrees. Yes the 2pdr is a much heavier gun but a lot of that is the carriage. It just took the British about 3 years too long to make the APCBC projectile.




Now maybe the 42/28 is the worst example of the German taper bore guns. Not light enough to get into the 28/20 class for easy transport and not big enough to get into the 75/55 size for actual better ballistics at 1500-2000meters.

Good points.

The info I gave was (I think) from the RAE tests vs tank armour, which included both 20mm rounds and the 40mm/3 lb AP Mk V round fired from the 'S' gun. If this is the case, they cloncluded that the same attack profile was appropriate.

Hurricane Mk IID Attack Profile with 40mm 'S' Guns:

Approach the target area at about 1,500 ft height in order to spot target effectively. Once the target is spotted, descend to about 1,000 ft AGL while out of range of AA but keeping the target in sight, then continue descent to minimum safe height (considered to be about 15-20 ft in the open desert) while turning into the target. Fire was opened at 700 yds and ended at 200 yds, after which an immediate turn away from the target was started while remaining at low altitude and using terrain if possible to avoid AA fire. Usually, this gave enough time for 5 shots of 40mm per gun. The .303 MG were synchronized with the 40mm at 500 yds. In training, it was found that ~25% of the shots fired hit the target. In the Far East, it was found that ~25% of attacks resulted in hits on target (25% of 10 rounds = 2.5 hits on average). NOTE that the Far East squadron was highly experienced.

At a distance of 100 miles from base the Hurricane Mk IID had enough fuel and ammo to make 3 attacks, with 30 minutes available to recon and spot targets, plus enough fuel to return home safely after exiting the target area.

In training, the pilots found that it was necessary to open fire at around 700 yds in order to have time to spot the fall of the first tracer rounds from the MGs and correct if necessary for the following shots. The 40mm/3 lb Mk V could be fitted with a tracer as well.

If we assume that the French could do as well, then that would allow about 40x 20mm rounds per gun (4 sec of fire at 600 rpm) going down range during the attack, with upto 10 hits per gun on successful attacks. One 20mm HS would allow about 10 hits, two 20mm would allow 20 hits, etc.

Shortround6 said:

Now maybe the 42/28 is the worst example of the German taper bore guns. Not light enough to get into the 28/20 class for easy transport and not big enough to get into the 75/55 size for actual better ballistics at 1500-2000meters.

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It is Autumn of 1940.
Germans can take a stock of how the heavier enemy tanks are protected + how good are their own guns and their ammo, and act accordingly. Like, if a gun cannot reliably pierce these tank at the distances of at least 500m, it is not worth making it if it is a new gun type, especially seeing that German light AT gun inventory is beyond 15000 (15 thousand) pieces with the captured guns counted. Or, anything under than the 5cm pak is not worth it.
The adapter might be a solution to bring the existing guns to a new standard of the armor-piercing level. Especially for the better captured guns, 47mm and above.
Experimenting with the new high power 75mm guns from the late 1941 with the adapter should've brought the AP performance to the level of the historical pak 41, again removing the need for the new gun type o be made.
Make the APCBC type of shot for the squeeze bore guns. That, and avoiding the 28/22 being made, will improve the ammo supply for the more powerful guns.

The Czech 47mm with APCR ammo was almost as good as the 42mm from 500 m and beyond, while the French AT 47mm with APCR was better than the 4.2mm.
(link)

A profound discussion of exotic ways of a very limited improvement in the characteristics of weapons, which in principle do not solve the problem, is undoubtedly prolific and greatly enjoys the topic starter.
But it has been said many times: before the GAU-8/A, all aircraft cannons used against tanks were extremely ineffective due to the high shell dispersion and the instability of the aircraft when firing. Tank losses caused by aircraft cannons were negligible - it is completely pointless to create complex and expensive systems with such effectiveness. Perhaps the Su-8 with a 4x45 mm battery could be an exception, but I am not really sure about that.