Probably relatively little. The round shape exhibits something similar to supercavitation, where it just smashes the air out of the way and flies in a little bubble of vacuum.danielrowell wrote:It would be interesting to see what would happen if GL was tested with a boat tail.
This reduces skin drag (a big factor with long walled projectiles at subsonic velocities) and causes a reduction in turbulence off the hard edges at the base of the projectile (the same thing a boat tail sets out to do).
Adding a boat tail wouldn't have as much effect as it does on a longer nosed bullet (which will have a laminar boundary layer around the nose and body).
One other method of reducing drag that is interesting, although not shown on the graph, is how much reducing the coefficient of friction of a projectile's surface can improve its drag coefficient.