I've written much on tank cannons, but what about their other weapon, the machinegun? While it is a less prominent feature of armoured vehicles, it should still not be ignored. Here is a comparison of American intelligence data from PAM 30-60-1 Vol. 3 Pt. 1.
The DT should be familiar to most WWII tank enthusiasts, as this was the go-to machinegun for Soviet armour. The post-war DTM is a slightly improved version that replaced it.
Starting with the T-54, the SGMT machinegun was used on new designs. The PKT is a tank version of the Kalashnikov machinegun, used on some T-55s, and all T-55As and up. All these machineguns use the good old 7.62x54r cartridge.
The next machinegun is the American Browning, which made it to this list by virtue of being used by the Yugoslavian army. Compared to the DT, it is heavier and fires slower, which grants it a higher effective range due to less scatter. Despite using a slightly faster round, it is slightly inferior at armour penetration.
The DShKT is a tank version of the DShK machinegun, used in a AA role. The IS-4 and T-10 used this weapon as a coaxial machinegun. The larger caliber achieves a much higher penetration and effective range.
The last machinegun is the even larger caliber KPVT, using the 14.5 mm round, same as the PTRD. The T-10M has this gun as both the coax and the AA machinegun.