I have not read it, but I have heard that the book "
Sniper on the Eastern Front: The Memoirs of Sepp Allerberger" by Albrecht Wacker, contains references to the "expolding" bullets.
Josef Allerberger - Wikipedia, the free encyclopedia
Another book I ran across seems to reference these rounds. It is a pricey book, but I would like to get it one day.
"The German Sniper 1914-1945" By Peter R. Senich
Amazon.com: German Sniper: 1914-1945: Books: Peter R. Senich
The V-Patronen (or B-Patronen as noted in the following link) round is sometimes mentioned. I can't vouch for it, but it is implied that the bullets were originally developed as "spotter" rounds used in aircraft machine guns. They were said to give off a small puff of smoke on detonation.
This site had some interesting info. regarding this type of round, as well as the "ZaRa" Russian bullet.
Gunwriters' Questions and Answers, Part 15
From the above link...
"German 7.9 mm B-Geschoss had a more prominent incendiary effect with less drastic explosion than ZaRa bullet. Striker mechanism was similar in both of these projectiles (copied from Austrian flat-tipped 8 mm
Übungs Geschoss Modell 1913). Shape was also identical with ZR. B-bullet was designed one or two years later than ZR bullet, but development of it was started about in 1930, presumably in collaboration with Soviet-Russians. (In Russia were many German designers and other "spezialists" until 1933, id est: To the end of
Weimar's Republic era and
Rapallo's Pact between Social-Democratic Germany and Socialistic Soviet Union. Russians got know-how and German designers got the safe workshops, out of sight of their relentless enemies. "Treaty" of Versailles banned all military development in Germany, until ADOLPH HITLER proved that "papers are nothing but paper" - including the Versailles' Dictates)."