I don’t believe the stories I read on the breathier biomimicry sites that bullet trains can reduce their fuel consumption by 15% just by having a beak-shaped nose fitted.
It seems, however, that Japanese engineers wanted to reduce the noise made by high speed trains on emerging from tunnels and they used the geometry of a diving bird’s beak to achieve a large noise reduction.
Today’s invention is therefore a way to suppress the noise from a firearm, based on this dynamically-similar regime.
Bullets would be made axially asymmetric, as indicated.
Although they would be less stable in flight, despite the usual rifling, and therefore only effective at lower range, when used with a conventional suppressor, I’d expect a decrease in report of a few extra dB.