AKMS, this is a tale and please should be erased from anyone’s memory and the one who promoted his opinion to such an extent is missleading people and should be punished because he is endangering them.
The Russian designation of this round is “VD” what stands for “vysokoe davlene” = “high pressure”. (the original color code for these was an all yellow projectile - to be observed with calibers where no special projectile got developed like the Russian 5.45x39). With the appearance of these special longer and heavier projectiles the yellow marking was dropped obviously. The Russian pre war 7.62x54R “VD” for example used also a regular projectile which was all yellow painted. An oddity is the (likely) one lot of Hungarian 7.62x39 with that longer and special projectile, it is also all yellow (thin translucent laquer), a duble marking so to say. Also interesting is that Poland and Romania developed for thier 5.45x39 “VD” a special projectile similar to the one in question above while Russia and the GDR did not.
The info that this is a measuring round is missleading people in a way that they may think it might be harmless to fire this round from a weapon. THIS IS NOT THE CASE AND MAY EVEN DO HARM TO THE SHOOTER AND DESTROY THE GUN!
The “VD” is a “barrel proof” round for barrels with a rifling and chamber in it without outer contures - when they are still outside a weapon (hence the longer projectile, it does not fit a magazine, just MHO). So if a test fired barrel has passed it will be furter machined to the final specs, this way a lot of work is saved in case a barrel does not pass.
Regular HPT rounds as you have indicated have an all black projectile. These are supposed to be used in assembled weapons. Their designation is “UZ” and stands for “usilenyi zaryad” = “enhanced propelling charge”.