I had the impression that the way the bullet is formed, it may cork-screw by design after leaving the barrel??
If it does spiral, it probably does not help accuracy, but at 20ft who cares..
If you stop this video at the 13 second mark, you can see the cork-screw propeller like cavitation action.
https://www.youtube.com/watch?v=VIh5...Sg5IqnZXcUfuau