Gary- the bottom one, a .40 barrel was an attempt at a very short cone - about 3/16" from a few thou larger than groove diameter, to the bore size. It worked OK but was of no advantage. That barrel was subsequently shortened for a 1/2 stock rifle and only the original .45 barrel & similar crown, shown with the .58 Enfield barrel, graces that stock now.
I use mainly 320 grit, wet or dry, or emery cloth - both done dry. I shove a piece of cloth down the tube first to trap stone/metal/etc particles, so they are easily removed when done. I usually start with a tapered stone (hardare store for electric drills)either spun by hand, or by an electric drill, with the cloth or paper wrapped around it - that takes only seconds to get the initial taper when using power. I finish with my thumb as that gives a nicely rounded crown, rounding and smoothing the corners - maybe 3 minutes to 5 minutes time.
The second one down, the .69, is my most accurate and uses the tightest combination with the largest powder charge, by far, was done entriely by hand, with my thumb and 320 grip emery cloth. That crown took about 15 minutes. The ball and patch combination it shoots, has .014" compression all the way around, in the bottom of the grooves. The ball and patch it uses measure .742", yet the groove to groove measurement isx .714". Subtract those two and you have .028" compression total, or .014" side to side, all the way around. It's tight, and maybe that is what makes it the most accurate.
I also use a 15 bore WW ball (Tanner Mould), .675" with the same patch. It too shoots accurately and loads about identially, maybe slightly easier. That one only has .0105" compression on each side, all the way around. They are not quite as accurate as the pure lead, larger ball but will go into 2" at 109 yards (100meters), good enough for hunting most game animals.
