While similar to the Soviet RPD/RPK, the TUL-1s were actually Chinese Type 56 assault rifles but with the stock of an RPK, barrel/sights from an RPD, and 30 round magazine used on the AK-47/Type 56. On rare occasions, they had 40 round magazines but almost never the 75 round magazine typically used in the RPK.
Follow Army Recognition on Google News at this link

TUL-1 light machine gun in the hands of a Vietnamese soldier (Picture source: VietDefense Facebook page/Lê Khang)

Because it used the frame of a Type 56 assault rifle, the TUL-1 body was thin, only 1 mm compared to the 1.5mm of an RPK. It was also heavier and had an inferior rate of fire compared to the RPK - the firing rate was only slightly better than that of an AK-47/Type 56. However, the effective range of the weapon was successfully increased.

It has a very low rate of fire and a strong recoil, but it compensates for this with high damage and very fast (for a machine gun) reloading. With a double magazine, it has a 1-second reloading record for its class, which, taking into account the high damage and good accuracy of shooting, makes it a very deadly weapon.

Thousands of TUL-1 LMGs were manufactured for use on the battlefields between 1970-1972. Production of the TUL-1 ended after Vietnam obtained production rights to the RPK itself.