The T-12 is a 100-mm smoothbore antitank gun mounted on a two-wheeled, split-trail carriage, with a single caster wheel near the trail ends. The long (8,484-mm) gun tube has a cylindrical, multi-perforated muzzle brake which is only fractionally larger in diameter than the thin barrel. The MT-12 variant has a winged shield angled to the rear on both sides and an additional recoil cylinder above the breech on the right. Both versions frequently mount infrared night sighting equipment.
The T-12 and MT-12 fire fin-stabilized, non-rotating rounds similar to those of the 115-mm gun of the T-62 tank. Muzzle velocity is 900 meters per second for HE and HEAT rounds or 1,500 meters per second for HVAPFSDS rounds. Maximum indirect fire range is 8,200 meters (Frag-HE). The effective direct fire range is approximately 1,000 meters (HEAT) or 2,000 meters (HVAPFSDS). The HEAT round can penetrate about 400 millimeters of armor at any range. The HVAPFSDS round can penetrate about 225 millimeters at 1,000 meters. The theoretical rate of fire is reportedly 14 rounds per minute; however, rate for aimed fire is only 6 rounds per minute, and the maximum practical rate is 10 rounds per minute.