Thread: M1A2 vs T-80U

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American APFSDS rounds for the 120 mm M256 gun are made of a depleted uranium alloy, not tungsten. Natural uranium is a mixture of several isotopes, typically 99.27% U238, with 0.72% U235, and traces of other isotopes. Enriched uranium, which is used as reactor fuel, is produced by removing U235 from a large amount of normal uranium and concentrating it in the enriched material. Once the enrichment process is complete, the bulk of the remaining uranium, now called depleted uranium, has only 0.25% U235 left. Depleted uranium is still mildly radioactive, but unless it is somehow ingested, or it gets into a wound, it is not a significant radiation hazard for its operators.
The US Army chose to make penetrators out of depleted uranium for several reasons. First, it was cheap. The Americans had thousands of tons of it lying around as a result of their nuclear industry, so material costs were minimal, unlike tungsten, which was significantly more expensive, and dependant on foreign sources. Second, it was dense. Uranium alloys weigh about 18.6 grams per cubic centimeter, which compares well with tungsten alloys. Third, it was pyrophoric. When small fragments of uranium are exposed to air they burst into flames spontaneously, creating a useful incendiary effect inside target vehicles.
The fourth (and most important) reason had to do with the way uranium acts under pressure. When it is alloyed with small amounts (0.75%) of titanium, depleted uranium becomes susceptible to adiabatic shear, which means it forms very narrow bands of weakness under pressure and shears off along those lines. As a result, the front of a depleted uranium rod tends to flake off in small fragments during penetration, always leaving a pointed chisel-like tip to face the oncoming armor. Tungsten alloys, on the other hand, do not fail by adiabatic shear (despite millions of dollars spent trying to make them do so). Instead, the front end of a tungsten alloy rod squashes out into a broad mushroom shape during penetration, much like the mushroomed head of a lead bullet. Since the tungsten alloy rod forms a wide nose, it has to make a wide crater in the armor, but the narrow nose of a depleted uranium rod makes a narrower, more energy efficient crater. Thus, a depleted uranium rod can make a narrower deeper hole in the target than a tungsten alloy rod can, using the same amount of kinetic energy.
The US Army currently has two 120 mm APFSDS rounds in service. The M829A1 entered service in 1988, in time for the Gulf War, where it served alongside the earlier M829, and earned the nickname "Silver Bullet" for it's outstanding performance against Iraqi armor. The M829A1 is a long heavy round, with a 4.9 kg penetrator that is 78 cm long from tip to tail. The heavy penetrator and long heavy sabot make the M829A1 rather slow, with a muzzle velocity of only 1575 m/s. Nonetheless, it's high L/D ratio of 33:1 and it's depleted uranium construction give it excellent penetrating power. The M829A1 is still the front-line round for American tanks in overseas hot-spots like Bosnia and Korea.
The M829A2 entered service in 1993, and uses a penetrator that is much the same shape as the M829A1, but is made of a new depleted uranium alloy with improved performance. The M829A1's long aluminum sabot has also been replaced by one made from carbon fiber. This lightweight sabot design, which reduced the sabot mass by 30%, was combined with an improvement in the propellant to produce a dramatic rise in muzzle velocity. The M829A2 comes out of the muzzle at 1680 m/s, despite the fact that its penetrator is marginally heavier than the M829A1's. The new sabot did cause few problems at first, such as an increase in corrosion and an occasional tendency to swell in humid conditions, but these problems have been corrected. The M829A2 is not stored overseas, and it is only shipped from America on an as-needed basis, so sudden crises will have to be dealt with using the older ammunition.
The M829A3, which is the advanced successor to the M829A2, is currently completing qualification. It is scheduled to begin equipping units in 2003. This round, like the DM53, is designed to tackle heavy reactive armor, and it has an advanced propellant system for increased velocity, and a composite sabot for light weight. Details about the system are still sketchy, but it promises to have excellent performance.

Russian APFSDS for the 125 mm 2A46 gun uses a distinctly different design than APFSDS rounds manufactured in the West. When the Russians first started making 100 mm and 115 mm APFSDS in the 1960s, they used steel penetrators rather than dense materials like tungsten or uranium. Since the Russians needed vast quantities of APFSDS ammunition (they produced some 20,000 T-62 tanks alone), manufacturing considerations played a very strong role in their ammunition designs. Steel was strong, easy to machine, readily available, and quite economical, so it made sense to use it for the penetrator. Although steel penetrators were not as effective as denser metals2, they performed well enough if they could be fired at high velocities.
To ensure high muzzle velocities the Russians chose a very lightweight sabot design, called a "ring sabot". This resembled a narrow disc around the center of the penetrator, and it weighed much less than the "spool" designs now in use in the West. The light rounds could be accelerated to very high speeds, and muzzle velocity was an unmatched 1800 m/s for early 125 mm rounds. However, using the ring sabot design meant that the penetrator's tailfins had to touch the barrel walls, to keep the projectile properly aligned while it was in the gun. These wide fins cause large amounts of drag, and Russian APFSDS rounds all slow down quite quickly, lowering their penetration at long range.
The other factor affecting Russian APFSDS design is the fact that the 125 mm gun uses two-part ammunition. The projectile and main propellant charge are stored separately, and loaded into the gun one after the other by a mechanical autoloader. This means that Russian APFSDS rods can only be as long as the stowage cells in the autoloader. On the T-72 the ammunition hoist doors are only long enough to let a 70 cm object through, so long projectiles like the M829A1 (78 cm long) simply cannot fit. This is the fault of the tank, not the gun, and is the price the Russians have paid for a compact autoloader system.
The Russians fielded a number of 125 mm APFSDS projectiles in the late 1960s and early 1970s, including the steel 3BM9, and the steel and tungsten carbide 3BM12, 3BM15, and 3BM17. These low performance rounds are no longer in front-line service with top Russian units, but many remain in storage, and large numbers were exported or licensed to client states. Many nations used them throughout the 1980s, and, in some cases, up to the present day. Iraq, for instance, was still manufacturing 3BM15s in 1991. A further series of rounds, including the 3BM22, 3BM26, and 3BM29, were produced in the late 1970s and early 1980s, but very little is known about them, and they were not widely exported. The next round, the 3BM32, entered service in 1984, although it was not shown to the outside world until it was offered for export in 1993. The 3BM32 is made of depleted uranium, unlike previous 125 mm rounds, and it has an enlarged redesigned ringsabot. The round is quite short, only 49 cm from tip to tail, and the penetrator weighs about 4.5 kg. The 3BM32's 1700 m/s muzzle velocity is good, but the wide fins make it slow down fairly quickly, so long range performance suffers.
The 3BM42 is part of the same generation as the 3BM32, with a very similar rod shape and sabot. It entered service in 1986, although it too was only revealed in 1993. The 3BM42 uses a tungsten alloy core, but this particular alloy is too weak to form the entire rod, so the tungsten is sheathed inside a strong steel casing to keep it intact. The projectile is longer than the 3BM32, at 57 cm, but its mixed steel and tungsten construction means its performance is worse. The 3BM42 has a 1700 m/s muzzle velocity, but its wide fins slow it rapidly, just like the 3BM32.
The next generation of Russian APFSDS is the 3BM42M, which is quite different from other Russian APFSDS because it uses a spool shaped sabot with frontal support flanges, and has narrow fins, like typical Western designs. The penetrator uses a longer onepiece tungsten alloy body, but few other details have been released so far. Deliveries of the round were supposed to begin sometime in 1998-99, but the state of the Russian economy may have delayed this.



APFSDS ammunition
Round Name Point Blank 1,000m 2,000m 3,000m 4,000m
America
M829A1 670 mm 620 mm 570 mm 510 mm 460 mm
M829A2 750 mm 700 mm 660 mm 610 mm 570 mm

Russia
3BM32 540 mm 510 mm 470 mm 430 mm 390 mm
3BM42 550 mm 500 mm 450 mm 400 mm 360 mm

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