I have a 26" #4 Contour Krieger barrel that is currently chambered in 6.5-284 NORMA. It has a low round count (fewer than 100 rounds), so I am hoping that the steel hasn't hardened to the point that it will make a re-chamber job difficult. I am considering having the barrel re-chambered to .264WM. How far would it need to be set back? Asked another way, how much barrel length would I lose in the process?