Look up "centerless grinding" images. Several different approaches. But the main takeaway should be accuracy vs more conventional turning methods.
Changing lanes,..... moving over into the fast lane in this discussion.
I tore apart a bic lighter the other day because it was written on the interweeb that the flint spring can be used as a replacement,MUCH softer R700 ejector spring. Taint so,meaning...it isn't even close to fitting. So bullocks on whomever thought that sheet up. But,what this pile of bic parts left is two baby sized knurl of sorts. Look at your crack.....err,bic lighter. See those cpl wheels that comprise the thumb wheel?
Now back into the slow lane.....
It wouldn't take much effort to "knurl" the bttm of a bullet's lube groove. Now,that is....in and upon itself worth a try but it's this next part(secret's for some) that really has my curiosity up and goes back to a knurled,swaged handgun bullet. Who's to say...rolling a bullet isn't,or can't make it more round? Like centerless grinding produces more round parts. So,if it's easy peasy japaneasy to knurl a cast bullet for lube retention,the by product,or value added is that it's more perfectly round. I tried to convey this on a popular BR website,way before this thread and was immediately shot(ha) down as..... "well,that's not how we do it" sort of thinking. It was adding a canelure to JB's as "one" way of curing what was the ailment in that particular thread. They couldn't get past,"why" preconceptions on canelures to see that there can be benefits to "rolling". Not disparaging.... goes to prove that certain info and ideas just can't be thrown out to the public however because of longstanding perceptions that say,"this is why".