I just did one on an attempt at an early Dickert Rifle. Starting at the base of the rod and working my way back from the base of the rod in 6 inch or so intervals, I drew a waist with a red marker around the middle of each section I wanted to work on. Then I shaved back toward the base and gradually rotated the rod until the entire waist had been shaved off. I tried to keep the marker dead center on the section over which I worked. But each pass went down toward the base on each of the intervals in order to build the taper. I tried to keep the marker waist braced solidly on the end of my bench so I could stop it from bending. I ended up with maybe fifteen passes or so, from about mid way down the rod.
I did not make my thimbles because it is too easy to buy them, but inlet the rear thimble first because I tend to be inept and that thimble can quickly become an obstruction to smooth entry of the rod into the stock. . I this case, because of a 32" barrel length and transitional look I wanted, I put the larger thimble up front. I tried inserting and and sanding in between each pass and the end product produced an even and gradual taper. The base end tapers beyond 3/8 inch, and the threaded tip goes on that. I like a wooden end on the tip, and can get the rod down to where a couple of parallel grooves at the tip aid in pulling out a firmly seated rod.
I have one of those holed tools you put in a vice, but can't seem to control it the way I can by shaving. Haven't used the shavings to start a campfire yet, though.
I had to strop or sharpen the knife in between each turns completion, and holding the knife and bracing the rod ended up being a touchy-feely thing that I had to try out and adopt. If your knife is sharp and held at the angle you learn is best, even passed will keep the rod round.
From now on I'll do all my rods this way.