jimmy101 wrote:the round may well be aerodynamically stable (and rifling isn't needed).
That's very debatable... it depends on your goal.
If you want to be able to fire rounds that will retain a good consistent ballistic coefficient and hit head on, rifling may not be necessary.
If your goal is accuracy and consistency of impacts, aerodynamic stability is far from enough. Most designs of airgun pellets are aerodynamically stable, but you'll not catch any serious shooter firing them from a smoothbore.
Rifling does more than just keep the projectile pointed in the right direction.