The successful, at least in terms of huge production volumes, WWII era AA guns in this size class, in particular the German 88 flak 18/36/37, UK 3.7", US 90mm, USSR 85mm, all had MV between 790-840 m/s.
Going for >1000m/s with 1930'ies metallurgy was probably biting off more than one can chew.
While indeed the metallurgy of the early 1930s will be hard pressed to reliably muzzle velocities going well above 1000 m/s, the metallurgy of the late 1930s and early 1940s might've support the 1000-1080 m/s MV range. Germans were pushing towards 1000 m/s already by 1935 with the naval Flak, while having the 70+ calibers long 75 and 88 mm guns in the pipeline. Soviets were pushing with the 57mm ATG.
I'd suggest that we don't criticize the French for trying to make what it seemed as a logical next step, but rather to criticize them for not making the 800-850 m/s 'step' across the board and in good/great numbers from the late 1920s/early 1930s. Like, for every gun of such ballistic qualities, they have had in their warehouses perhaps 3, 4 or 5 guns of very sedate ballistics, talk 550-720 m/s (and these making 700+ m/s was a rare breed). It is not like they didn't know how to make good if not great guns - their naval and casemate guns were often with MVs of 850 m/s and above, so were the 25mm ATGs and (rare) AA guns - however, the land-based cannons and heavy AA guns were left behind in that regard.
People might raise a point of the barrel life, and rightly so. However, in a real war, the high MV AT guns will probably be destroyed before the barrel is worn out, while the removable barrel lines were a known quantity. Also the whole replacement barrels.
What might come as a bane to the mass introduction is the high price for the very long-barreled guns, and the ability of industry to churn out the required number of barrels.
People might raise a point of the barrel life, and rightly so. However, in a real war, the high MV AT guns will probably be destroyed before the barrel is worn out, while the removable barrel lines were a known quantity. Also the whole replacement barrels.
this was a very promising path, it just didn't have enough time. It really needed the tungsten carbide core to work.
Using a steel penetrator only works at rather close ranges. The small steel projectile just sheds velocity too fast for longer range work.
I have checked and it's confirmed Brandt had worked on tungsten carbide cores "of high density" already in the 25mm caliber in June/July 1937. The central state laboratories were to inform him of tunsgten production/acquisition potential in France as well as machining processes for tungsten carbide to help him in his endeavour. Thinking about it, the transfer of a tungsten mine's ownership to Brandt before the war (snatched by the Germans after the defeat before it could become operational) might be related to this.
More realistically, the likely main supplier of a hypothetical French tungsten ammunition effort in 1941-43 would probably have been Canada which produced a lot in WW2, to the point where the American industries couldn't refine it all.
I have an appendix to a certain textbook for students' military training, where for the A-19 the service life is specified as 1200-1500 rounds, and this service life is determined by the extension of the charging chamber. This may be post-war technology, but for wartime I can assume a minimum life of 800-1000 rounds.
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.
That principle was used on the Croatian RT-20 anti-material rifle, that went under 20 kg despite using the high-power 20mm Hispano cartridge. For comparison, the Solothurn S18-100, that used a lower-powered 'short Solothurn' cartridge, went to 40 kg. See here the short video of the RT-20 firing (somewhere in Croatia?), with the gunner uttering some cuss
Just ran across this again. You need a lot of gas to actually cancel out much recoil. Most recoil guns used 3-4 times the amount of propellent as conventional gun give the same ballistics.
The formula for recoil is projectile weight times muzzle velocity for bullet momentum (BM) + propellent weight times gas velocity* for gas momentum for the total momentum.
Now you can divide the recoil impulse by the weight of the gun to figure out the recoil velocity of the gun (or the recoiling part/s unchecked by dampers/springs) and then we can figure out the recoil energy (weight of the gun (or recoiling parts) times the velocity squared.
* for most small arms the gases exit the muzzle at around 1200m/s give or take 10% unless the barrel length is really abnormal.
Now to put this into small arms a 7.62 x 51 has BM of 8.32 (after dropping a lot zeros to get a manageable number) and the gas momentum of 3.58 for a total of 11.90
Now it we take 10% of the gas and direct it backward we may be able to reduce the BM by 10% (very optimistic, it is probably closer to 5%) and we can take 10% off the gas momentum
so the new numbers are 7.49 and 3.22 except we have to add in the forward thrust of 10% of the gas momentum so the total becomes 10.35 or just about 87% of the recoil impulse of the gun without the port and tube. You can make the port bigger and tape off more of the gas but there are few problems with that. Lower velocity of the projectile is one. The other problem is that you can't fire the weapon in an enclosed space any more or with walls/obstructions close the back of the weapon.
Actually a decent muzzle brake will reduce the recoil as much or more.
Now we can argue about the gas from the barrel port being higher pressure than the gas at the muzzle which is true but turning the gas rearward costs something and getting the gas back behind the gunner/crew is also going to cost something.
For a 20mm Hispano we have a 128gram bullet/projectile and about 29 grams of propellent. You need to tap off a fair amount of propellent to cancel out the weight of the projectile.
Edit, just watched Ian McCollum's video on the RT20 and he claims that the system cost about 25% in velocity. Lowered MV from about 830m/s to about 620m/s which doesn't make much difference to HE ammo but real reduces the impact of AP. Basically it cuts the Hispano down to about the velocity of a Japanese type 99-1 or German MG FF.
Gun is light for a 20mm but it does use a substantial muzzle brake and recoil is best described as very substantial.
The gas ports cut down the pressure in the barrel cutting velocity and the short barrel also cuts velocity. It worked for what they wanted but it not a system to to use on a kinetic energy AT gun.
Having recently obtained 93 inventories of the French Châtellerault archives (Séries H and F for ground equipment and armament research respectively), I now know where to look for plans of most French service and prototype guns even up to the Cold War period, as well as reports on ammunition and gun trials.
They indicate that the Atelier de Constructions du Havre (AHE) explicitly had a 90mm AT gun in development in 1939/40, likely based on the 90mm CA 39 they were producing. The list of names of plans would suggest it used a circular platform ala 25 pdr.
The picture below also discusses trials of a 75mm mle.1897 refitted with a "Rémy" type muzzle brake, shooting AP ammo at 640 m/s, with the powder charge to be determined using BG4 powder, which AFAIK is more suitable for higher performance guns than the BSP powder used in regular mle 97 AP loads.
I will finally be able to find reports on the following subcaliber ammo:
- 75/58mm Brandt shot from mle 97 compared to regular mle 1910 APHE
- 37mm Brandt
- 37mm Brandt modified by the Central Armament Production Laboratories (LCFA in French)
- 37mm LCFA 416g (APCR using service 25mm ammo as the core).
As promised, my first day at the archives this week focused on plans. We can finally have a look at the French 37mm AT gun project from 1940 and the 90mm AT gun project from December 1939. The latter clearly displays a carriage similar to the British 25 pdr, with a circular platform and a single tail to traverse the gun rather than a split-trail carriage.
With my recent research, I am now able to more accurately explain the development of French 75mm antitank guns between 1938 and 1940.
New firing pieces (note from September 7th, 1939):
4 new firing pieces were in development at this point: three designed for a muzzle velocity of 640 m/s by the APX, ABS and AHE design bureaus (Puteaux, Bourges and Le Havre), and one designed for a MV of 700 m/s by the AHE design bureau. The 640 m/s guns retained the chamber and case of the Mle 1897, but were designed for a service pressure of 260-270 MPa instead of the 240-250 MPa of the regular Mle 97. They differed in the following ways:
- APX barrel had a muzzle brake which extended shot travel by 200mm and added an extra 5 m/s ( 645 m/s), 270 MPa service pressure
- ABS barrel as used on the ABS 75mm 1939 project extended shot travel by 313mm, 260 MPa service pressure for 640 m/s
- AHE barrel extended shot travel by 413mm, 652 m/s at 270 MPa or 640 m/s at 260 MPa
All retained the Mle 1897 case which was known to be safe at these pressures, and trials with the ABS gun would confirm this. However, the powder charge would be increased from the 700g of BSP powder in Mle 1897 to about 900g of BG4 powder (same type as for the 47mm SA37 AT gun). There was concern as to the projectile mounting, which would most likely require 2 driving bands instead of one and/or deeper grooves. It appears, based on trials of the ABS gun, that the choice was to use 2 driving bands (the forcing cone in the chamber would be moved accordingly), a diameter of 76.4mm at the bottom of the rifling and an inclination of 8° instead of 7°.
Regardless, it was known and expected that the resulting complete ammunition would not be compatible with the old Mle 97, but that older Mle 97 ammunition could be used. This is a similar scheme as the American postwar 90mm M36 tank gun compared to the wartime M3.
All this applies to the AP round. For the long-range HE, derived from designs for the Mle 97, there were options for a loading of 870g BG4 giving a MV of 665 m/s and a range of 14.5-15km at 270 MPa, or 760g BSP giving 640 m/s and 14-14.5 km range at 260 MPa. For Mle 1915 common HE, they proposed 3 charges giving 8500, 7000 and 5000m max range.
In the case of the 700 m/s barrel by AHE, this was a L40 barrel (2544mm shot travel, 3m total bore length) which used a new case that is a little shorter than the AA gun case (about 480mm instead of 518mm). This was designed for a service pressure of 290 MPa. For the AP round, it would use either 1060 g of BSP powder at 685 m/s or 1150 g of BG4 at 700 m/s, if the recoil system handles that charge without too much fatigue. Long-range HE would be shot with a 1000g charge at 715 m/s (AA gun shot a heavier shell) to minimize wear, reaching 16 km. Common HE would be based on the Mle 1915, but with an improved profile to reach the range of the Mle 1917 shell when shot from the Mle 1897 gun; that is, 11 km. If that "improved Mle 1915" is used in the Mle 1897 gun, range would reach 10 km. Existing Mle 1910 APHE can't be used at 290 MPa, so new production Mle 1910 or the new Mle 1940 APCBC would be used.
What is interesting is that the document confirms that the French 75mm AA gun was weak for its class because the case couldn't use a service pressure higher than 250 MPa. The AP round used a 1270 g BG5 charge to achieve 715 m/s at 240 MPa. So in effect, the new 700 m/s gun used its improved technology to reach nearly the same muzzle velocity (15-30 m/s less) with a 10% smaller powder charge, a slightly shorter case and a 10-caliber shorter bore, the latter being the most important.
Conversely, an AA gun designed around the 260-270 MPa of the 640 m/s class would correspond to the overspeed test of the regular gun, that is 755-760 m/s with 1330g of powder.
An AA gun designed around the 290 MPa class, or a "700 m/s class" gun designed around the bore length and case dimensions of the AA gun, would most likely reach close to the performance of the US 76mm M1 tank gun (792 m/s, 296 MPa).
New guns:
I am linking the reports for the ABS and APX AT/field guns. The APX was meant as a stopgap gun which would mate the Mle 1897 firing piece and the 97/33's recoil system to a new split-trail carriage to replace the ageing Mle 1897 regular carriage. This increased the horizontal traverse arc to 60°, much better than the few degrees of the Mle 97. Unfortunately, the design in its present state was too flawed, the antitank equipment (sight) was defective and the carriage too complex for a stopgap, yet not as good as a completely new system. It was rejected unless simplifications and improvements could be made.
The ABS gun, commonly called the TAZ (tous-azimuths or 360° traverse), was gun that used the 640 m/s ABS barrel and a three-trail mount. It could be fired with 1, 2 or 3 trails set up, with the main configuration being 2 trails, like a classical split trail gun. When set up this way, it still has a very wide horizontal traverse arc of 76° at all angles and 93° at elevations below 18°. It was recommended for adoption on May 11th, 1940, once the choice was made as to whether to use the automatic breech mechanism and to choose either the 640 or 700 m/s barrel. It is rather heavy though, at 2000 kg when set up and 2090 kg when ready to move, requiring the help of another gun crew to move it easily. It's possible that, down the line, the French would have also designed a lighter split-trail carriage optimized for AT use only.
The French conveniently made a graph that showed the impact of upping the AP projectile velocity to 640 or 685 m/s. The Y axis shows the limit angle, the X axis the range at which behind-armor effects are obtained on 40, 60 or 80mm plate. It's clear that 50 or 60mm of armor on German tanks was never really an issue, but the main takeaway here is that the more powerful guns were practically essential to defeat 80mm of armor at several hundred meters, though from what I have seen of 75mm AP trials, 570 m/s did a little better with modern ammo. As of 1938-1940, the French were extensively testing new 75mm AP which eventually culminated into the 75mm de Rupture Mle 1940, of which at least 50 000 were ordered before the invasion, so in the process of industrialization. This would also be mated to the AA (715 m/s) and naval guns (850 m/s, given to the Army).
The Mle 1940 was a solid shot APCBC, replacing the Mle 1910 APHE which had no cap or ballistic cap. It is thus more similar to British APCBC, or to American APHECBC except that it had no explosive filler. This configuration was also adopted for new 90 and 105mm AP rounds after meetings on December 14th and 15th of 1939 decided to abandon all APHE designs. Solid shot had been shown to offer slightly better ballistic and AP performance, eliminated problems tied to APHE (premature detonation), and was cheaper to produce.
We previously discussed the strange French steel-cored 37mm APCR projectiles. It turns out that unusual designs were also being developped for 75mm and 105mm calibers. The former would use a 53mm core, the latter would directly use the body of the 75mm Mle 1940. Both with cap and ballistic cap. What is stranger however, is that they were mated to a heavy steel body/non-discarding sabot and were thus not much lighter or faster than full-bore ammunition.
Per a document on AP ammo development, it seems that French engineers had identified a mechanism wherein the core and body would both count for the penetrator weight until the body split away when hitting the armor plate, while it is the core diameter which would count. The end result being a non-negligible increase in penetration, presumably owing to a greater kinetic energy density for the area that was hit.
A list of the reported estimated penetration figures (all at 30°):
75mm 640 m/s class gun at muzzle:
75-40-4 (APCR, MV 655 m/s): 82mm if Rho=1.4, 103mm if Rho=1.2
75-39-13 (APCBC, MV 640 m/s): 57mm if Rho=1.4, 71mm if Rho=1.2 (worst case, APCR gains 12mm)
75 Brandt (APDS, MV 966 m/s): 80mm if Rho=1.4, 100mm if Rho=1.2
75mm 640 m/s class gun at 500m:
75-40-4 (APCR): 72mm if Rho=1.4, 90mm if Rho=1.2
75-39-13 (APCBC): 50mm if Rho=1.4, 63mm if Rho=1.2 (worst case, APCR gains 9mm)
75 Brandt (APDS): 71mm if Rho=1.4, 89mm if Rho=1.2
105mm Mle 1913 gun at muzzle:
105-40-3 (APCR, MV 550 m/s): 103mm if Rho=1.4, 128mm if Rho=1.2
105-40-2 (APCBC, MV 520 m/s): 72mm if Rho=1.4, 90mm if Rho=1.2 (worst case, APCR gains 13mm)
105mm Mle 1913 gun at 500m:
105-40-3 (APCR): 93mm if Rho=1.4, 116mm if Rho=1.2
105-40-2 (APCBC): 65mm if Rho=1.4, 81mm if Rho=1.2 (worst case, APCR gains 12mm)
I will note that Rho corresponds to a coefficient which is inversely proportional to projectile quality, so the lower, the better. French subcaliber ammo generally had around 1.4 in testing, so a lot more testing was desired to improve this figure.
Development of 37mm APCR was also not over, since they ordered that 100 000 of the Brandt Mle 1935 APCR would be converted with a proper ballistic cap to lose velocity more slowly and stay more effective and accurate at range; and a new design called 37-39-3 would be tested. The latter used a smaller 19mm core instead of 22mm, but would carry a proper ballistic cap and an armor-piercing cap to improve performance against cemented steel.
Development of 37mm APCR was also not over, since they ordered that 100 000 of the Brandt Mle 1935 APCR would be converted with a proper ballistic cap to lose velocity more slowly and stay more effective and accurate at range; and a new design called 37-39-3 would be tested. The latter used a smaller 19mm core instead of 22mm, but would carry a proper ballistic cap and an armor-piercing cap to improve performance against cemented steel.
tomo pauk
A rather unexpected breakthrough happened. I was googling Brandt APDS once again, and stumbled on this website (old so it will send you an alert message for protection), which gathers PDFs of Brandt pamphlets/reports on AP, AA and artillary ammunition developped in the late 30s, sent to the US Ordnance and found in the US archives: https://tacticalorganization.com/edgar-brandts-ammunition-projects/
As far as AT goes, the relevant docs discuss:
- 25mm APCBC with steel, higher-density tungsten steel or tungsten carbide cores
- 37mm APDS with steel or tungsten carbide cores
- 37mm APCBC
- 47mm APCBC
- 75/58 APDS
- 105/80 APDS
Plus some results for 13.2 and 7.5mm calibers of using tunsgten carbide cores. There is also a picture of such a projectile for the 20mm Hispano.
They notably discuss penetration trial results, but also ballistic benefits of 75/58 in particular.
Notable examples, the 37/25mm to the left and 75/58 to the right.
To nuance the trials results, it's also worth noting that some of the projectiles in question lack an AP cap, that the 75mm is shot from the regular Mle 97 and not from any of the more powerful 75s under development, and that the 105/80mm projectile reuses the old Mle 1910 APHE as the core, so there was substantial leeway to improve performance.
This is a veritable gold mine, indeed Many thanks for finding this and providing the link.
I've found the doc listing the development of the AA shells also very interesting, cutting the flight time by a large margin would've improved the hit (and thus kill) probability by a lot. The artillery shells were outfitted with an ... outrageous aerodynamic cap (far bigger than what the eg. the French had in offering in 155mm calibre, or what was used on the contemporary naval shells) to improve the streamlining and thus reduce drag for the better range. One shell design probably benefited due to the 'hollow base' it had.
Also, the APDS shots were with the aerodynamic cap, unlike the British ww2 developments.
Seems like the doc covering the 37mm APDS is missing, the link is for the (repeat) of the field artillery ammo development by Brandt.
It would've been interesting to know how much the Germans were informed about these developments after the fall of France.
This is a veritable gold mine, indeed Many thanks for finding this and providing the link.
I've found the doc listing the development of the AA shells also very interesting, cutting the flight time by a large margin would've improved the hit (and thus kill) probability by a lot. The artillery shells were outfitted with an ... outrageous aerodynamic cap (far bigger than what the eg. the French had in offering in 155mm calibre, or what was used on the contemporary naval shells) to improve the streamlining and thus reduce drag for the better range. One shell design probably benefited due to the 'hollow base' it had.
Also, the APDS shots were with the aerodynamic cap, unlike the British ww2 developments.
Seems like the doc covering the 37mm APDS is missing, the link is for the (repeat) of the field artillery ammo development by Brandt.
It would've been interesting to know how much the Germans were informed about these developments after the fall of France.
37mm APDS is already discussed in the general AP file and the 37/26 file, so there probably wasn't another APDS file, or it wouldn't be that important.
The Germans reportedly knew about 75/58 and one was captured by the Wallies in Paris in 1944, but German APDS developments took their own path.
What I'm more curious about is the US. The author of the web page claims that these docs were sent to the US Ordnance, and indeed these were found in the US archives. Yet APDS development at the New Mexico laboratory still failed to get a lead on the British, and seem different again. The DTIC file on APDS development in the US does not mention the French at all.
Both it seems, approved by Vichy. He later sent his close associate Colonel Delalande to the US.
tomo pauk
Interestingly enough, the Brandt docs on 75mm ammo mention that APDS uses a charge of 960 grams at around 245 MPa and long-range HE used 1010 grams at 260 MPa, although in the latter case the point was to test the maximum potential of the ammo.
So the 350R case has a little more leeway than the 900 grams I had found for 640 m/s guns. Whether such a load can be used at 270 MPa while actually increasing muzzle velocity is unknown. For regular Mle 97, I think the real limiter is the recoil system, but the Brandt APDS with greater KE but lower momentum avoids this issue.
Though Brandt APDS already uses a higher charge, I guess 270 MPa in the 640 m/s would give a little higher MV, around 985 m/s instead of 966 at equivalent KE with APCBC. The 700 m/s gun gives 1085 m/s.
The APDS is nice, but the APCBC for 25, 37 casemate and 47mm is also interesting. Brandt explained that he generalized ballistic caps (not new) and more importantly uses slightly subcaliber steel, tungsten steel or tungsten carbide (25mm only) cores jacketed in the light alloy ballistic cap. This was to not only use the subcaliber effect, but also use shorter cores with higher ogival angles which are better at preventing break-up and maintaining penetration against angled armor.
The point isn't always to enable penetration of even thicker plates, but to stay effective against already threatened thicknesses (30, 40, 50, 60, 80mm) at higher angles and greater distances.
The side bonus is slightly increased velocity and a flatter trajectory. APDS is even better but more complex.
I also note the 105/75mm APDS ends up providing very similar ballistics to the 76mm M1 (APDS becomes 75mm APCBC in flight, muzzle velocity of 775 m/s instead of 792 for the 76). Turns every Mle 1913 field/fortification assault tank gun into the 3rd most powerful French gun behind the 75 Mle 1908 naval gun (850 m/s) and the 90mm and derivatives.
Semi-offtopic, gun Jesus has a new video about a 6.5mm APDS that can be used in guns chambered for 9mm Parabellum with just a barrel change. It has a tungsten penetrator, and armor penetration outperforms the standard 5.56 rifle round with a hardened steel penetrator. Pretty impressive.
The video emphasizes the need for the sabot to depart cleanly and uniformly from the penetrator to get consistent results (accuracy). As we have seen the idea dates back to the late 30s (?) but turning the idea in workable ammo/weapons took a while longer. British seem to have done OK with the 6pdr and not so well with the 17pdr although the 77mm using the same projectiles seems to have done OK. Actual test results are a bit lacking. US did not use APDS in the 90mm guns used in the M-26,M-46, M-47 and M-48 tanks. The US did not adopt APDS in large tank guns until they adopted the 105mm guns in the M-60s and that was a British gun using British developed ammunition (at least the APDS). The British had spent quite a bit of time developing the 83.4mm (20pdr) APDS in the 1940s.
Accuracy standards can be relaxed in emergencies. Like when your standard rounds won't penetrate the enemy tank/s at just about any range. But poor accuracy gives you a dilemma.
You don't have a lot of APDS in the 1930s/40s because you don't have a lot of Tungsten. So you can't use it a long range because you don't hit as often as the standard rounds and if you only score 1 or 2 hits before you run out of APDS ammo where are you? If you wait to get closer you can get more hits but then, depending on gun/projectile, you may have a decent chance of penetrating with a non APDS projectile.
The video emphasizes the need for the sabot to depart cleanly and uniformly from the penetrator to get consistent results (accuracy). As we have seen the idea dates back to the late 30s (?) but turning the idea in workable ammo/weapons took a while longer. British seem to have done OK with the 6pdr and not so well with the 17pdr although the 77mm using the same projectiles seems to have done OK. Actual test results are a bit lacking. US did not use APDS in the 90mm guns used in the M-26,M-46, M-47 and M-48 tanks. The US did not adopt APDS in large tank guns until they adopted the 105mm guns in the M-60s and that was a British gun using British developed ammunition (at least the APDS). The British had spent quite a bit of time developing the 83.4mm (20pdr) APDS in the 1940s.
Accuracy standards can be relaxed in emergencies. Like when your standard rounds won't penetrate the enemy tank/s at just about any range. But poor accuracy gives you a dilemma.
You don't have a lot of APDS in the 1930s/40s because you don't have a lot of Tungsten. So you can't use it a long range because you don't hit as often as the standard rounds and if you only score 1 or 2 hits before you run out of APDS ammo where are you? If you wait to get closer you can get more hits but then, depending on gun/projectile, you may have a decent chance of penetrating with a non APDS projectile.
One might note that the 1841 zündnadelgewehr or Dreyse Needle Rifle used a lead egg shaped bullet in a wrapped paper sabot. The standard Prussian infantry rifle until after the 1870 War.
You don't have a lot of APDS in the 1939/40 because people didn't designed and have it manufactured?
If one does not push beyond 1000 m/s with the APDS - and most non-AA and non-Navy guns will not in that time - one can do with hardened steel.