The M829 has a ballistic nose and five tail fins made of aluminum. It is carried in the gun tube by a three-piece aluminum sabot, which separates into three "petals" soon after the round leaves the gun tube. The propulsion system uses an obturating case base with a semi-combustible cartridge wall. It has a total weight of and utilizes a DU penetrator with a rod diameter, which will reach a muzzle velocity of using of of JA-2 propellant. Maximum effective range is. According to Jane's, the M829 is capable of penetrating of RHA steel armor at up to a range. The original M829 is no longer in production and has been succeeded by the M829A1, M829A2, and M829A3. The corresponding training round is the M865 costing $1,121.
M829A1
The M829A1 proved itself in 1991 against Iraqi T-55 and T-72 tanks during Operation Desert Storm. The M829A1 round weighs and has an overall length of. The of JA-19 propellant creates a chamber pressure of 5,600 bars, which results in a muzzle velocity of. The -long penetrator together with its sabot weighs. The mass of the penetrator alone is. The effective target range is.
M829A2
The next generation ammunition, called 120mm APFSDS-T M829A2, entered service in 1994, and is the current armor penetrator ammunition being produced by the General Dynamics Ordnance and Tactical Systems for the 120mm M256 gun of tanks M1A1 and M1A2. It is a technology improvement over the M829A1. The new ammunition's performance gains, while classified, result from several new features. These include the use of a special manufacturing process to improve the structural quality of the depleted uranium penetrator. This, plus the use of new composites for the sabot, which, together with a new propellant, provide superior penetrator performance. Combined, these features increase the muzzle velocity of the M829A2 approximately 100 m/s greater than the M829A1, while operating at slightly lower pressure. Projectile length: 780 mm; weight: 9 kg. On 6 May 2014, the US Army announced that it awarded a US$12 million-contract to defense contractor General Dynamics for the demilitarization and disposal of 78,000 aging depleted uranium tank rounds as newer rounds are added to the U.S. war reserves. The contract includes M829A1 and M829A2 rounds.
M829A3
The M829A2 was the immediate response, developed in part to take on this new ERA type. The M829A3 is a further improvement, designed to defeat any future armor protection methods like 'Kaktus' ERA, which was seen on the now cancelled prototype tank, the T-80UM2 "Chiorny Oriol" tank. It completed type classification standard in March 2003. Very little is publicly known about the round, perhaps due to export restrictions. The M829A3 uses a more efficient propellant, RPD-380, boosting its muzzle velocity. The M829A3 round has a total mass of and length of. It uses of RPD-380 stick propellant, accelerating a depleted uranium rod penetrator, which can be estimated from cutaway mock-ups to be long, to a muzzle velocity of. From patents submitted by Orbital ATK, the penetrator is composed of two sections, an approximately 100 mm long steel tip and the rest composed of depleted uranium. The penetrator diameter was also increased from to, improving penetrator strength by 67%. This suggests the steel tip is used to defeat the ERA, with the depleted uranium using to complete the penetration through the vehicle's passive armour. Resulting muzzle energy is 12.1 MJ. The sabot is of composite material. This variant is unofficially referred to by Abrams tank crews as the "super sabot". It costs around $8,500. Although the M829A3 fired from the 44-caliber M256 gun has a lower muzzle velocity than 120 mm shells fired from the Rheinmetall 55-caliber gun barrel or Russian 2A46 125 mm gun ammunition, it uses a larger penetrator with increased mass to increase imparted kinetic energy.
M829A4
The A4 variant was under development by General Dynamics Ordnance & Tactical Systems and Alliant Techsystems until ATK received a $77-million, three-year contract on 11 July 2011 to develop and qualify the M829A4 Advanced Kinetic Energy round for the US Army's M1A2 SEPAbrams MBT. The M829A4 is a fifth-generation APFSDS-T cartridge consisting of depleted-uranium penetrator with a three-petal composite sabot; the penetrator includes a low-drag fin with a tracer, and a windshield and tip assembly. Its propellant maintains consistent muzzle velocities across operational temperatures from. The new Advanced Combustible Cartridge Case is similar to previous models but has a relocated skive joint placement for better crew-member safety during handling. The initial order for 2,501 M829A4 rounds in 2014 had a unit cost of $10,100 each. On 20 July 2015, Orbital ATK announced that the M829E4 had passed First Article Acceptance Testing and was entering production. On 12 October 2015, Orbital ATK announced the round had recently received type classification as the M829A4, and was awarded a full-rate production contract to begin in early 2016.
