Competition Over Nothing
At the start of the Great Patriotic War, two design bureaus worked on rifle grenades: KB-30 and A.K. Serdyuk's SKB-35. In November of 1941, grenades from both organizations were tested at the Small Arms Research Proving Grounds. Serdyuk's VPGS-41 grenade was already in service with the Red Army. The KB-30 design was experimental.
Trials showed that the VPGS-41 reliably penetrated 20 mm of armour. However, there was a significant drawback: the stabilizing fins fell off the grenade more than half the time. The testers recommended that the design should be improved and gave Serdyuk until February of 1942 to do it. By then, he had to provide a new test batch of 500 units.
The KB-30 grenade, which used a small cup to fire, penetrated less armour, but proved to be a lot more stable. The army ordered ten times more grenades of this type than the other to send them to trial in combat. Since the grenade was never accepted into service, one can only assume that the results were unsatisfactory.