There have been many discussions on the War Thunder forums about prototype tanks equipped with a 140mm gun, as well as plans and implementation proposals. However, most of these discussions have focused on the penetration power of the APFSDS and the protection capabilities of the hull, and have not touched on the numerous APFSDS prototypes or their structure.
Therefore, in this forum I would like to focus on the 140mm APFSDS prototypes and their structure.
I’ll say this in advance: I did my best to gather sources, but since it would be impossible to do it manually, I also used AI to gather information. I made sure that the AI did not use unreliable sources and that it only used primary and highly reliable secondary sources, and I also did my best to scrutinize the sources, but using AI may have included incorrect information or oversights. If this happens, please feel free to let me know. Also, please feel free to share any useful materials.
Of course, this is not the place to insult, slander, vent complaints, or attack specific users, so such behavior is strictly prohibited.
There is a proposal to implement a prototype tank with a 140mm gun in the game, so I will display the links below.
Information on prototype tanks equipped with 140mm and 152mm tank guns
Overview of the 140mm gun project
First, let me outline the 140mm gun plan. Simply put, it was based on information about tanks developed by the Soviet Army in the late 1980s that had extremely high defensive capabilities, featuring thick composite armor and heavy ERA. Western countries felt a sense of crisis that their existing 120mm guns would no longer be able to destroy these tanks, so they researched and developed a tank gun with a muzzle energy of over 20MJ to be able to destroy them.
The above information is widely known, but in fact the 140mm gun project was not simply about destroying powerful Soviet tanks; it also involved significant research and investigation, such as investigating the structural limitations and technical expandability of the APFSDS itself, conducting in-depth research into the combustion of propellant charges through repeated firing tests with the 140mm gun, and studying changes in barrel life due to chamber pressure, as well as the impact of recoil and the vehicle body.
Also, at the same time as the 140mm gun project, research was being conducted on tungsten alloy APFSDS, which had a low density of 17.6 and a problem of limited penetration power due to the mushrooming phenomenon, by adjusting the composition to increase the density to 18.0 or more and overcome the mushrooming phenomenon. As a result, the 140mm gun’s APFSDS had a high penetration power thanks to the tungsten alloy penetrator, which had a density of 18.0 or more and overcame the mushrooming phenomenon.
Furthermore, the technologies developed during the 140mm gun project are still being applied to the current 120mm gun and its ammunition, as well as the next-generation 130mm gun, making it extremely important.
Generally, when you try to look up data on the 140mm APFSDS, you’ll often find information circulating that the muzzle velocity is between 1650m/s and 1900m/s, a wide range of reported flight weights from 7kg to over 10kg, and penetration power ranging from over 800mm to 1024mm.
Of course, these aren’t rumors because there are multiple pieces of information circulating, but rather because there were actually a huge number of prototypes for the 140mm APFSDS, each with a wide variety of performance and characteristics.
In other words, the existence of prototypes means that the information you get will vary depending on which source you read, or even which part of the document you read from the same source, and this is why there are such large differences in the data.
Also, as I will mention later, the 140mm APFSDS did not have a monoblock structure with a main body made of tungsten alloy and depleted uranium alloy like modern APFSDS, but rather had a structure like the M735 and 3BM42 in which the penetrator core was wrapped in a steel sheath in order to withstand the intense muzzle energy of the 140mm gun.It is also important to note that, unlike the APFSDS used in typical 120mm guns, which has a long, slender shape with a diameter of about 25mm, the 140mm APFSDS had a diameter of about 45mm including the core and steel sheath.
Steel sheathed structure
Nearly all modern APFSDSs use a monoblock structure, because the tungsten or depleted uranium alloy used in the penetrator core can withstand the energy of firing.
However, the story changes when it comes to a 140mm gun. For example, the force exerted on an APFSDS during firing—say, a core with a diameter of 30 mm (cross-sectional area of A approximately 7.07 x 10^{-4} m}^2) and a weight of 10.5 kg—is fired from a 7m-long barrel. At a muzzle velocity of 1650 m/s, the force reaches approximately 2.89 GPa, and at a muzzle velocity of 2000 m/s, the force reaches approximately 4.24 GPa.
Because the yield strength of tungsten alloys is 1.2-1.5 GPa, and that of depleted uranium alloys is 0.8-1 GPa, the APFSDS would not be able to withstand the force and would become distorted or even crack if it were not fitted with a sheath.
The maraging steel used for the sheath has a yield strength of 2GPa to 2.4GPa, so it is used to encase the core.
As an aside, the earliest APFSDS were made from maraging steel, or had a core encased in maraging steel, because of its high yield strength.
Prototype in the United States
Looking at the table, it seems that the bullets with the highest L/D ratios and those with penetrator core lengths reaching 1000mm would be able to exert a high penetration force, and the values calculated using the L-O formula show high penetration forces.
However, because these bullets have L/D ratios that are too high (too slender), they would bend upon impact when actually fired, and the ratio of steel sheath to core would be too large, reducing penetration force, so they were not adopted.
Furthermore, the thickest sheath, which applied technology from the 155mm HE projectile, had a diameter of 54mm, making it extremely resistant to ERA, but its excessive weight resulted in a slow muzzle velocity and insufficient penetration.
The heaviest projectile was 16.5kg for the APFSDS body alone, and 21.5kg including the sabot. However, because the weight was so excessive, the muzzle velocity was only 1520m/s and the recoil was excessive at 1600kJ.
For reference, one of the US 140mm gun projects involved using nitramine-based high-energy propellants to raise the chamber pressure to 900 MPa in order to test the limits of the barrel. However, even if a 16.5 kg APFSDS (21.5 kg including the sabot) was fired at this chamber pressure, the calculated muzzle velocity would stagnate at around 1630 m/s to 1740 m/s.
Prototype in Germany
In this case, as with the American prototype, the penetrators were too long and thin, which resulted in accuracy problems due to distortion and shaking when fired. Also, penetrators that were too thin were not adopted due to concerns that they were vulnerable to ERA resistance.
The problems with the heaviest and thickest scabbards were similar to those of the American prototypes, and the reduction in muzzle velocity was a serious issue.
Prototype in French
In France, a prototype with a core diameter of just 18mm was created in an attempt to improve penetration power, but it was found to be vulnerable to ERA and was not adopted.
The thickest sheath was 48mm in diameter, which is not as thick as those used in Germany or the United States. This was because it was not for testing the rigidity of the APFSDS, but for testing the recoil of the Leclerc’s hull.
However, the heaviest specimen exceeded the Leclerc’s recoil tolerance and was therefore not adopted.
Regarding prototypes in other countries, we have omitted them because we could not find any notable prototypes. If you have information about prototypes in other countries, please let us know in the comments section.
The need for a formula that takes into account the steel sheath
Currently, War Thunder does not have a calculation formula that takes steel sheaths into account. APFSDSs with a penetrator core encased in a steel sheath, such as the XM578, M735, and 3BM42, are implemented in the game, but the sheaths are only a few millimeters thick, so there are no major issues with calculation formulas that ignore the sheath’s thickness.
However, the sheath of the 140mm APFSDS is over 10mm thick, so ignoring the sheath’s thickness can result in calculations that deviate significantly from the historical penetration value. For example, for a penetrator core longer than 900mm, the formula will calculate a penetration value of over 1000mm, while for cores shorter than 800mm, as actually used, the calculation results will be limited to 700mm to 900mm.
Therefore, a calculation formula that takes steel sheaths into account is essential.
Density of Tungsten Alloys in Games and the Need for New Standards
While the game accurately reproduces the physical dimensions of APFSDS cores based on historical data, it employs standardized density values for the core materials: 7.85 for maraging steel, 17.5 for tungsten alloy, and 18.6 for depleted uranium alloy.
However, this approach presents issues; a notable example is the DM53 APFSDS, where the tungsten alloy density is calculated as 17.5 in-game—resulting in reduced penetration—despite manufacturer specifications listing it as 18.5.
Early-generation tungsten alloy APFSDS rounds had densities of only 17.0–17.6 and suffered from the “mushrooming” effect, which limited penetration. Research conducted during the 140mm gun project and concurrent programs sought to increase density while suppressing this mushrooming, raising the figure to around 18. Modern generations have further advanced this technology, maximizing tungsten alloy content to achieve a density of 18.5; these rounds have overcome the mushrooming issue and attained a “self-sharpening” effect, albeit not quite to the same degree as depleted uranium alloys. Had tungsten alloy density remained stuck at 17.5, it is easy to imagine that the 140mm APFSDS would have failed to achieve 1,000mm of penetration, and APFSDS rounds for 25mm–40mm autocannons might have been rejected due to insufficient penetration performance.
To summarize, I believe the game should implement a tiered density system that reflects the evolution of tungsten alloy generations.
Specifically, a three-tier approach would be appropriate: maintaining a density of 17.5 for pre-140mm gun project generations; setting the density to 18 for the transitional generation—including the 140mm APFSDS and the 152mm APFSDS developed by the Soviet Union during the same period; and setting it to 18.5 for the latest generation of APFSDS. This is expected to alleviate, to some extent, the previous issue where penetration power was unreasonably low due to the use of standardized in-game values.
The importance of the steel sheath
In the simulations shown in this video, both cases assume a depleted uranium alloy core measuring 25.5 mm in diameter and 780 mm in length, with the simulation conducted using the bare core in both instances. While the LOSAT example serves merely as a reference—given that a steel sheath was unlikely to have been used in the actual historical configuration—the M1 CATTB simulation shows the core snapping due to the ERA, resulting in a level of penetration capability that barely achieves a breakthrough.