The main armament of the T72B3M / T-72B4 consists of one 2A46M5 125-mm smoothbore gun which is a modernized variant of the standard 2A46M cannon, also known as the D-81TM. This gun system features reduced recoil and a stabilized gun mount. The 2A46M-5 variant was introduced in March 2012 as part of the upgraded T-90MS tank. The 2A46M5 gun design made it possible to reduce the technical dispersion of shells of all types by 15% in average and to increase the effective range of fire. It can fire a full range of ammunition including APDS (Armour-Piercing Discarding Sabot), HEF(High-Explosive Fragmentation), HEAT (High-Explosive Anti-Tank), and GM. The cannon can also fire the 9M119 Refleks (NATO designation AT-11 Sniper) anti-tank guided missile system. The range of the missile is 100m to 4,000m and takes 11.7 sec to reach a maximum range. The system is intended to engage tanks fitted with ERA (explosive reactive armor) as well as low-flying air targets such as helicopters, at a range of up to 5 km. Like all T-72 series MBT, the T-72B3M is fitted with a carousel automatic loader mounted on the turret floor and also on the rear wall of the turret. The new gun was added including an upgraded stabilization system and autoloader. A 7.62 mm PKTM machine gun is mounted coaxially to the right of the main armament and has 250 rounds of ready-use ammunition. One 12.7 mm NSV heavy machine gun is mounted on the commander's cupola. A bank of 8 smoke grenade dischargers is mounted on the left side of the turret.

The layout of the T-72B3M / T-72B4 is similar to the standard T-72 with the driver at the front, fighting in the center, and the power pack at the rear. The tank has a crew of three, with the driver seated at the front center of the hull. The other two crew members are seated in the turret, with the gunner on the left and the commander on the right. The T-72B3M is protected with the new Relikt explosive reactive armor. It will replace the old Kontakt-5 system and is expected to be two times more effective. Developed by NII Stali, Relikt utilizes a completely new composition of explosives to achieve dynamics protection. Unlike Kontakt-5, it works equally reliably against both low-velocity and high-velocity missiles, doubling protection against shaped charges and increasing anti-tank guided missile protection by 50 percent. Relikt defends against tandem warheads and reduces penetration of APFSDS rounds by over 50 percent. The side skirts are now T-90 style, including the large flat ERA modules. Two light steel stowage boxes are mounted on the turret, one at the rear and the other on the right slightly behind the commander's position.