Alternative light and anti-tank guns, 1935-45

[Shortround6]

It's clear that even the superior performance of tungsten carbide doesn't invalidate the merit of steel cores as long as long as your gun didn't achieve 900-1000 m/s with full-bore ammunition. In the case of Brandt 75mm, you're talking about a 53mm core at 966 m/s, making it possibly more powerful than 6 pounder full-bore ammo. Even when using a 640 or 700 m/s class 75, you could still go with a slightly heavier core (say 60mm) to stay around 1000 m/s. The advantage of subcaliber ammo is that going for lighter but faster rounds can yield performance increases without exceeding the limit of your recoil system, as momentum can be reduced or kept constant.

All very true.
The other question/s are what is the expected engagement range? The high velocity stuff extends the engagement range as the lower drop in trajectory makes it easier to hit at long range, assuming the dispersion doesn't got to hell at the longer ranges.
APCR looses velocity faster than normal shells so it's advantage at longer ranges is not as marked (doesn't exist at all for the smaller calibers) while APDS shot, using carbide cores, has a marked advantage at long ranges, assuming decent dispersion pattern. Steel cored APDS may or may not have much an advantage depending on size of the core, initial velocity and range.

This is actually sorta the period when more mobile carriages for high-speed traction start development. That said this just means that traditional carriages were ok for 30kph while the new carriages would be good for 50-70 kph.

Some armies (Italian?) rated the some of the traditional carriages at 20kph tow speed. Most horse drawn artillery was not towed at the gallop. In some armies the crew walked along side the guns/limbers. There was a large gap in speeds that went unexploited. Motor tractors that could tow at 20-30kph could have significantly increased army mobility while reducing the need for horses. Heck, even being able to tow at 15kph average for 8 hours was well above what horses could do and a 120km advance in a day was a big advance.
But you need somewhat better carriages to do even that.

France already prototyped low-velocity 75mm howitzers in the 20s and 30s so little need for using the B1's gun here, if the concept had been retained

Now we get into the difference between low velocity guns and howitzers. You can use the same projectiles and the same barrels and even the same basic cartridges.
But the howitzers are going to want to be able to use 3-5 different powder charges to adjust the trajectory.

Using the German 7.5cm infantry gun as an illustration, the gun itself only weighed 400kg so it was easy to handle, compared to a 'standard' field gun. It fired a 6kg projectile with a rather decent HE content. It used 5 different powder charges so the gunners could vary the velocity from 92ms to 210ms which allowed the gunners to drop shells over some tall intervening terrain/building if need be.
As an ersatz AT gun it runs into problems. Original HEAT shell of 3kg was fired using the original charge 5 load for 260m/s and while rated for 45mm of penetration that is a bit reduced in service. Also trying to hit at anything except very close range was problem. Even if we forget about wind resistance (drag) it had about a 3 second time of flight to 750yds and forget about the target moving, the projectile will drop 24.5 meters in the last second of flight and that is after dropping 14.7 meters in the 2nd second of flight.
German designed a new projectile with a bit better penetration and crimped the shell into the cartridge case with it's own powder charge that gave 345ms mv that significantly increase the chances of hitting at close range. Like adding 90-100 meters of effective range.
You also have to careful balancing the weight/velocity of the shell to the weight gun/howitzer.

this weapon could not use charge 5 at less that 15 degrees elevation as the gun bounced around too much.
Despite the 750kg weight and the muzzle brake the Germans used charge 4 to fire a 4.4kg HEAT shell at 390ms.
German only ran the graduations on the sight out to 1000 meters for this shell.

There is only so much you can do due to physics even using tricks like muzzle brakes.

 

[tomo pauk]

The British 47mm guns in the 1920s were pretty much 1880s guns that had the black powder propelling charges replaces by smokeless powder without change the ballistics much. They might have produced some new barrels but kept the old ballistics.

If they picked the 47mm Vickers, that would've allowed them to have ballistics in the ballpark of the Czech or the French ATG 47mm guns.

Problems with any successful use of a 47mm (3pdr) gun in British service requires NOT using the mounts (tank and towed) and projectile types that the 2pdr was stuck with.

Not trying to reinventing the wheel with the 2pdr gun and carriage leaves a lot of time and a nice sum to make better AP stuff, as well as the better and timely HE stuff.

Just imagine 6-8 men on foot (or with 1-2 horses) trying to cart around a worthwhile number of 75mm HE projectiles.

No need to imagine that. That was a reality in many armies, and the French and British would've have it easier since they had more off-road going vehicles and trucks the the Germans or Soviets in the 1930s.

The 75mm in the hull of the Char B. It was only an AT gun because the German tanks used such thin armor.............and got really close to the French.

470 m/s with plain AP ammo, 40mm at 400m @30 deg.
Crew of the best German tank in AT job in 1940 - that of the Pz-IV - would've loved having such a gun on their tank, even if that is just because of extra MV.

 

[Elan Vital]

All very true.
The other question/s are what is the expected engagement range? The high velocity stuff extends the engagement range as the lower drop in trajectory makes it easier to hit at long range, assuming the dispersion doesn't got to hell at the longer ranges.
APCR looses velocity faster than normal shells so it's advantage at longer ranges is not as marked (doesn't exist at all for the smaller calibers) while APDS shot, using carbide cores, has a marked advantage at long ranges, assuming decent dispersion pattern. Steel cored APDS may or may not have much an advantage depending on size of the core, initial velocity and range.

The images under spoilers are the dispersion and ballistic results using the current and Brandt APDS projectiles for the 75mm Mle 1897, resulting from 1939 trials. Note that the Brandt has an extra advantage of having 791mm of recoil against 929mm for the full-bore round, showing the much lower momentum.


Dispersion-wise (496m), the table shows results for new and worn guns. What it shows is that the Brandt displays a ca. 35% increase in dispersion over the fullbore round.
However, with the table on the left showing the trajectory at 500 and 1000m, you see that the much shorter flight time and flatter trajectory results in a much lower max trajectory height (1.25m instead of 3.78m at 500m, and 6.2m vs 18.5m), and much smaller corrections for wind or enemy vehicle speed (half of those for the service round).

In practice, since hit probability is heavily succeptible to errors in the target distance, wind and vehicle speed, the APDS more than makes up for its increased dispersion. In terms of penetration (that was with steel or tungsten steel, not sure which alloy), the APDS was superior at any realistic range. The benefits would be smaller against the new Mle 1940 APCBC owing to said BC, and the AP cap improving performance against cemented plates, but still significant. APCR with a good BC may still be better than full-bore ammo.

In this case we are talking about, Brandt was talking about up to 1000m of practical range, which was indeed quite common in WW2. More than that becomes difficult even with good guns owing to the various gunnery errors.

Spoiler: Brandt 75 ballistics

 

[Shortround6]

Not trying to reinventing the wheel with the 2pdr gun and carriage leaves a lot of time and a nice sum to make better AP stuff, as well as the better and timely HE stuff.

Problem is that the British didn't want to pay for better AP stuff, or the HE stuff, even when they went to the 6pdr guns.
It was price/doctrine and perhaps not in that order. The British were making a crap load of 2pdr HE shells for the Pom-Pom guns and it took until the end of 1942 to actually load any into 2pdr AT gun cartridges and even longer to get any to the front lines.
Expecting much different when going to the 47mm may be expecting a lot.

No need to imagine that. That was a reality in many armies,

Problem here is the use. A Field gun battery was not 4 or 6 guns towed by 4 or 6 teams of horses and few guys in a wagon as a HQ. There were an extra caissons, one or two per gun in addition to the caisson/limber attached to the gun with horse teams as immediate ammo supply and many armies added several 4 wheel ammo wagons per battery.
Field gun battery of 4 guns could have 8-12 horse teams moving the ammo and more moving the HQ and communications.

AT gun batteries were not expecting to fire scores or hundreds of rounds of HE in day.

470 m/s with plain AP ammo, 40mm at 400m @30 deg.

Something is off here. Either French figures or German figures.
Most sources (wrong?) claim the German short gun in the Pz IV was good for 39mm at 500meters@ 30 degrees with it's standard (not HEAT) round.
Penetrating 1mm less 100meters further away does not sound like there was a huge need to change over to Gun performing like the French one.
German round is supposed to be (wrong?) an APCBC round and not a plain AP round?

Crew of the best German tank in AT job in 1st 1/2 of 1940

Fixed it for you
From the summer of 1940 they were putting the short 50mm in the MK IIIs. A bit short sighted as it turns out but it meant the MK IVs could stay as support tanks.

 

[tomo pauk]

Problem is that the British didn't want to pay for better AP stuff, or the HE stuff, even when they went to the 6pdr guns.
It was price/doctrine and perhaps not in that order. The British were making a crap load of 2pdr HE shells for the Pom-Pom guns and it took until the end of 1942 to actually load any into 2pdr AT gun cartridges and even longer to get any to the front lines.
Expecting much different when going to the 47mm may be expecting a lot.

British were investing into n all-new gun, and into an expensive carriage, plus were designing the edditional 6 pdr (despite the RN already spending the money on a epon that can do 90-95% as good). Going 'normal' saves them pretty penny that can be used to get the better ammo.
Vickers 3pdr as-is will be a better hole puncher than the 2pdr, with the ammon of same type.

AT gun batteries were not expecting to fire scores or hundreds of rounds of HE in day.

Nobody expects them to do so. The HE ammo for the AT guns is like the AP ammo for the field guns - having 10, 15 or 20% of that ammo ready to use improves the worth of these pieces in combat.

Something is off here. Either French figures or German figures.

Both Germans and French say 470 m/s.

Most sources (wrong?) claim the German short gun in the Pz IV was good for 39mm at 500meters@ 30 degrees with it's standard (not HEAT) round.
Penetrating 1mm less 100meters further away does not sound like there was a huge need to change over to Gun performing like the French one.
German round is supposed to be (wrong?) an APCBC round and not a plain AP round?

APCBC-HE, at least that is per the October 1939 manual.
German tankers would've appreciated the increase of MV by 25%.

 

[tomo pauk]

Germans almost ended up with the reasonably powerful 75mm L40 gun very early on the future StuG-III; gun was supposed to be firing the 6.8 kg AP projectile at 685 m/s:



Tests in 1940 were convincing on what was hoped for, and gun was outfitted with the muzzle brake. Note also the rapid fire, eg. 10 rounds in 25 seconds; there is also one firing done at over-pressure (greater propellant load?), pushing the AP shot to 700 m/s :



Propellant charge was ~1.67 kg, or almost double of the French 75.

 

[Elan Vital]

Rheinmetall-Borsig designed the Kanone 37 L/41 with the same ballistics (same specs given by the HWA?), used on the Pz Sfl II:

I notice that:
- these guns are extremely similar in length and ballistics as the French 700 m/s gun, albeit with a 6.8kg proj instead of 6.4kg
- the propellant mass is considerably greater, 600 grams more than the French gun at 685 m/s and 500 more at 700 m/s.
- the service pressure is around 260 MPa, more in line with French 640 m/s class guns and 75mm M3, while French 700 m/s class gun runs at 290 MPa. This may explain the greater propellant mass along with the heavier projectile. When tested at 290 MPa, the German gun achieves 700 m/s.

Speaking of pressures, it seems that in the end the French 90mm AA gun which served as the basis for 1940 tank and AT guns was a 260 MPa class weapon. A 270 or 290 MPa class weapon like US hot load 90mm and British 17 pdr could yield some more power (or keep same power with a smaller case and/or shorter barrel).

 

[tomo pauk]

I notice that:
- these guns are extremely similar in length and ballistics as the French 700 m/s gun, albeit with a 6.8kg proj instead of 6.4kg
- the propellant mass is considerably greater, 600 grams more than the French gun at 685 m/s and 500 more at 700 m/s.
- the service pressure is around 260 MPa, more in line with French 640 m/s class guns and 75mm M3, while French 700 m/s class gun runs at 290 MPa. This may explain the greater propellant mass along with the heavier projectile. When tested at 290 MPa, the German gun achieves 700 m/s.

From the German point of view, the L40 (L41? maybe these were the same guns, or at least the ammo was the same - I'll look at it more closely*) gives at about 90% or the MV and energy as the future L48 tank gun. Ballparking it and being on the conservative side, that might mean the penetration, at 30 deg, of 85+ mm at 500m, and 75+ mm at 1000 with the Pzgr 39 shell. That level of performance keeps them very happy in 1940, and it is still very useful in 1941,in 1942 (by what time the improved HEAT shell should've been available), and even in 1943.
With the Pzgr 40 shot, it looks like 105+ or 85+ mm at 500 and 1000m, respectively - a convincing level of AP performance for any war year.
(not that this should preclude the development of the better guns, obviously)

And all of this in a gun that is very easy to install even on the light vehicles, as well as on a Pz-IV and Stug-III, and whose ammo is not oversized (very important for a vehicle-mounted gun). But the main advantage, that they missed on, was that the gun have had a perfect timing.

* this L40 gun seems to be Krupp's product

 

[Elan Vital]

Something else that caught my attention again is how the Brandt subcaliber AA ammo relates to APDS for certain guns.

The Brandt 105/80 APDS weighed 8.73 kg including 6.935 kg in flight. 775 m/s MV

The 105/85 HEDS for the same Mle 1913 gun (used for AA) weighed 7.08kg including 6.51kg in flight, with 852 m/s MV. Lighter sabot resulting in less difference between complete and in-flight weight?

The 90/80 HEDS for the 90mm CA 39 weighs 6.61 kg including 5.795 kg in flight at 1040 m/s. This involves a lower muzzle energy than the fullbore APCBC round (11.2kg at 820 m/s).

The hypothetical 90mm rebored to 105mm (a L42) fires a 80mm 6kg projectile (complete it seems?) at 1220 m/s. This is at 230 MPa while the Mle 1913 shot its APDS at 235 MPa.

In comparison, the German 75mm KwK 42 L70 shot 6.8kg APCBC at 935 m/s and a 4.75kg APCR at 1120 m/s. 17 pdr shot a 7.7kg APCBC at 900 m/s (IIRC a lil more for new barrels) and 3.5kg APDS at 1200 m/s.

Unless the sabot remains as heavy relative to the rest of the projectile as on the 105/80 APDS, seems like the 90mm and theoretical 105 L42 can achieve good performance with subcaliber ammo, on par or somewhat better than the 17 pounder (not that surprising as the French and US 90 and British 17pdr were in very similar classes) and German 75 L70 (a weapon that is 75cm longer).
The theoretical 105 isn't even that powerful, it's quite low pressure compared to other guns firing subcaliber ammo and the barrel length is not too high. An hypothetical late-war French 105mm with a L50 barrel and a service pressure of 290 MPa or more could get quite a big boost for subcaliber ammo.

 

[tomo pauk]

I've probably mentioned this before - but for the Germans, going with the ammo & barrel from the 7.5cm Flak as the base for the new AT gun would've perhaps bought them a few months, or much more if that idea dawned on them.
(LW didn't wanted these, so the Navy adopted them as coastal Flak)
Ammo is less clumsy, too, with casing being 640mm long vs. 714 for the pak 40 - might come in handy on a vehicle installation. Propellant weight was some 2.4kg as used on the Flak, where it was propelling the 6.5 kg shell at 860 m/s from a L60 barrel. Plenty enough of power to deal with many ww2 tanks, even before looking at better ammo types, or/and how to load it hotter.

 

[tomo pauk]

Different ways to square the circle of the HEAT shells not being that good when firing from the rifled guns. One approach involved the introduction of the shell that has the expandable fins (Klappleitwerk in the doc below); the development is finished (with what results - it does not say). The way of avoiding the rotation by the rifling must be found (drallfreie = non-rotatting). Another thing that was mooted was the very high MV for the HEAT ammo, 1000 m/s; that is commented as being the 'uncharted territory' (Vollkommenes Neuland). A way to have that from the 105mm howitzer was supposed to be the under-calibre (10,5/7,5 Kal.) shell with discarding sabot (TS).
The last sentence says that big problems (grosse Schwerigheiten) still lay ahead.