The DT-29 machine gun, accepted into service in 1929, was installed on almost all models of Soviet armored vehicles until 1945. At the end of 1941, a barrel with simplified cooling fins began to be installed (Late barrel, the same will be on the DTM).
The presented barrel with developed cooling fins can be seen on vehicles extract 1930-1941.
The presented barrel (late type) can be seen on most domestic tanks and armored vehicles, starting from the end of 1941.