If you are doing your own work, then do as Jerry says and get a set of pilots to go with the reamer. That way you can use a rod to insert the pilot into the barrel to find what sized pilot fits your bore. Keep going up in size to find the largest pilot that won't fit into the bore and then drop down a size to one that will. However, you don't want it so tight that it scars the top of the lands when the chamber is being reamed. If you aren't doing your own work and are having a benchrest gunsmith do your chambering, then don't worry about pilot size as he'll use a pilot that fits the bore, but get a reamer with removable pilots and not a solid pilot. With a .237" bore, you might find that a .2368" works or you might find that a .2372" works. You just don't know until you check the bore with the pilot set or with a set of pin gauges. In the original post it states that the bore is a .237" bore and then the last post states .236" bore. Pacific makes two different sets of pilots for 6mm's, one for .237" bores and one for .236" bores. The sets are a set of 9 pilots in .0002" increments. Of course, the .2365" pilot will not fit in a .236" bore, but will fit in a .237" bore.
