The theory behind the use of dimples on golf balls and others is that they create pockets that hold air, and that air rubbing against air involves less resistance than air rubbing against metal. There is a slight gain in velocity using a dimpled ball, but at the short ranges where round ball are shot- you can't change their ballistics Coefficient, which is next to horrible!- the difference is not worth the extra effort involved.
To work properly, the dimples would have to be of uniform size and shape, Rolling a lead ball over a rasp would give you uniformity of shape, and depending on how much control is used in the pressure put on the ball during the operation, you may be able to control the depth of the dents. On the First Pass. However, on subsequent passes, it would be next to impossible to have uniformity in the sizing and spacing of the " dimples" using this method, and multiple passes would be needed to dimple the entire circumference of the ball.
Others have put the balls in tumblers, using a uniform grit, or even shot, to dimple the balls. They report better accuracy. We don't know if this is due to the fact that tumbling tends to remove any air pockets, or due to the new dimples.
There is a problem with a dimpled ball coming down through the sound barrier staying on course. Golf balls don't usually exceed the speed of sound, so its not a problem in that game. Whether there is any measureable improvement in the flight of a round ball at sub-sonic velocities that would justify the extra treatment to created uniform dimples, I don't know, and frankly doubt.
There are so many other factors that contribute to shooting PRBs accurately, that separating out dimples to test that one factor would require a wind tunnel, at minimum, and maybe a large vacuum chamber. Considering the obturation of the PRB in the rifling, and the misshapen lead projectile that leaves the barrel as a result, its hard to believe that any dimpling could overcome all these other factors.
Every Round Ball I have recovered clearly shows the lands and grooves, and most show the weaving in the cloth patch that was used in firing the PRB out the rifle. PRB shot out of smoothbore tend to be more oval shaped than round, and, depending on caliber or gauge, can actually show fattened sides where the ball upset in the barrel.
Keep in mind that the Round Ball is a projectile that was designed and intended to be shot at fairly short ranges. We hear of people shooting targets using the PRB at 200 yds, and no doubt it can be done. However, most RB are shot at 50 yds, or less, with 100 yds, considered to be the maximum distance you want to use them in a hunting situation, using traditional rifles or smoothbores, and open sights. The PRB has been used for more than 500 years. If something would make it more accurate to shoot, It would have been discovered more than 100 years ago, when the Industrial age began, and the PRB was at its height of use in both military and civilian applications. They may not have understood the aerodynamics of a golf ball back then, and their understand of ballistics was fairly primitive, but they put to test any idea that came along. There still exist round ball rifles made during the 1840s that exhibit extraordinary accuracy, and were used to shoot record scores in their day. You have to think that if people were capable of making accurate rifles back then, they would have also figured out some way to make round balls fly truer, too.
