I have been shooting N-SSA competition smoothbore for over 5 years now. I was taught to rough up my balls by rolling between two files. I made a little fixture to hold one file in a wooden trough, where I could put in the ball and then apply the other file on top. This works, but was tedious and made my hands hurt. It was also very time consuming.
I then made a machine to do it:
http://forth-armoury.com/vortex-ball-roller.html
This is the device that duelist1954 reviews.
What rolling the balls between files does is
increase the diameter of the ball. It also obliterates the sprue. But mostly, what it does is increase the diameter of the ball
while still being able to be loaded.
I shoot an RCBS .678 round ball in my .69 caliber Armisport M1842 smoothbore. When I rough up the bullet, it increases in diameter by about .010"
This video demonstrates this growth in size:
My balls were dropping about .680. By roughing them up, they grow to just under .690.
So why not just use a bigger ball? Well if you use a bigger ball, it might not load at all, especially after the barrel gets fouled. But by roughing up the ball, you end up with "whiskers" all over the ball that
effectively increase its diameter, eating up windage in the barrel, but those whiskers are deformable and so will give way during loading if necessary.
You can think of it like this: If you squeeze a ball of playdough in your hands, it will ooze out between your fingers. The total mass of playdough has not changed, but the effective diameter has gotten larger.
In addition to roughing up the balls, I coat them after roughening with Alox. This is
not lubricant. Rather, it becomes another coating of "windage eater" on the outside of the ball that will scrape/wipe away on loading if needed.
I tried
only dipping the as-cast balls in Alox, hoping to avoid roughening all together. Unfortunately the Alox tends to flake off the smooth surface of the round ball. It sticks tenacioiusly to a roughed-up ball.
Unfortunately I don't think Duelist1954 gave my device a fair shake. Just roughening up the balls by itself won't help with accuracy. If you still have a loose fit in your bore after roughening, then you probably won't see any difference in accuracy.
Roughening up the balls simply eats up windage in the barrel. It's like using a patch. If your bullets don't fit tightly after roughening, then you won't gain any benefit from the roughening.
My balls fit my bore so tightly that I often get an "air piston" effect on loading and have to be careful when I let go of the ramrod after a stroke because the compressed air can launch the ball+ramrod right out of the muzzle if you are not careful when you let go of the ramrod for the next stroke.
Again, this is for competition shooting.
Steve