I use a steel template that has holes drilled in it from 3/8's to 5/16th's down in 1/32" increments.
I table saw my shafts to size 3/8 always watching for good grain , then chuck the shafts in a drill and run it thru the 3/8 hole knocking off the edges, next hole a little tighter but so on till its at the proper diameter to be close to the spine I need then hand work till she's perfect!
Got the idea from the Traditional Bowhunter mag a long time ago and have used that templater to make many shafts! Works good!