I've got a .308 bull bbl that I'm considering turning into an octagon sporter. But, my books are not helpful and I know nothing. I'm not even sure what questions to ask. End milling or side milling? Up milling or down milling? Lots of light passes, or fewer medium passes? Temperature control ?Last thing I want to do is induce warpage, it is a pretty good bbl. How many holdown fixtures to get good rigidity? My machine is a small but very heavy, combination horizontal and vertical, American made mill (too small for the job, really, but time means nothing on this project). If it wasn't a rifle bbl it would be a pretty straightforward machining operation, but having some experience straightening bbls I am fully aware that bbls want to warp, and any mistreatment will let them have their way. Any tips would be greatly appreciated.