I do, in fact, use a patched round ball in my rifle. However, my thoughts on tumbling them was that if they were more smooth and spherical, they might fly a bit more true. This would be due to a more lamnar flow of air over the surface of the ball. Most assuredly, the air flow is not perfectly lamnar in either case but I suspect that the closer one comes to achieving a perfect lamnar flow, the truer the ball flies. The effect of having random imperfections on the side of the ball in flight is the reason many shooters will make a conserted effort to load their balls with the sprue up. I am not an aeronautical engineer so my suppositions are based upon my limited training in college physics. I could be wrong but I don't think so.
You've got the right idea but it's not going to work in THIS case.
I've designed, built and flown model airplanes for much of my life and studied at a hobby level aerodynamics out of intrest in making a better model.
A round ball will see laminar flow over the front half and for a very short way around the waist. Let's consider the side view of a ball flying through the air. The 9 o'clock position is the front. By the time the air flows to the 1 o'clock and 5 o'clock points it's already separating from the surface and turbulating to form a highly tubulent wake.
The dimples on a golf ball act as surface flow invigorators, sometimes called turbulators as well. This busts up the laminar flow early and forms a thinner but "sticky" thin turbulent layer that effectively bonds the laminar flow a few thousandths of an inch above the turbulent layer to the surface much better than a truly clean laminar flow.
If we take a dimpled BP ball and look at the airflow the laminar flow will now follow around the waist of the ball and not spearate until more like the 2 and 4 o'clock points. This doesn't sound like much but the cross section area of the wake is now probably 1/2 or less than it was when it separated at the 1 and 5 o'clock points. That becomes a HUGE reduction in drag and dimpled golf balls fly probably 1.5 times further.
On a golf ball there's no way to know how it'll turn and spin so it has to be totally covered in dimples. With our BP balls the spin ensures that the same point is always facing forward. So if we were to cut or mold some rings in the forward side of the ball just before the waist it would do the same thing as all the dimples on the the golf ball but with the advantage of some small amount of actual laminar flow before the air hits the invigorator rings.
The problem is that now you need to load the ball with the ring evenly placed. Not something that would work with a long rammed home rifle barrel but perhaps with a cap and ball revolver it would work. Then you need some way to test for drop at something like 200 yards to see how they compare.
For anyone with a lathe to turn the grooves it would be easy to do. Or if you can make a cup to hold the ball you can even form the groove by hand.
