If I had cut the chamber I would be able to tell how much head space your rifle has in thousands, a chamber cut by someone else? No problem, purchase new cases or purchase a few once fired cases from the range, cut them off in front of the belt, because it does not matter make it one inch, if you reload size the cut-off cases then try to chamber, if the test cases chamber without resistance to bolt closing check the chamber length from the face of the bolt to the shoulder of the chamber, again new or once fired cases will work, I cut the belt off of the case, neck the case up to 338 or 308 (I use a 308 Norma Mag or 338 Winchester Mag sizer die) then start necking the cases down with the 7 Remington Mag die, BUT, with a feeler gage, adjust the die off of the shell holder with the ram up, I start with a gap of .012 thousands, after moving the shoulder back attempt to chamber, if the test cases will not chamber, decrease the gap to .008 and attempt to chambering the cases again, if you do not get consistant chambering before you get to .000 gap, the chamber is short, I will not say 'not a problem' I would adjust the die down to the shell holder with an additional 1/4 turn (what ever that is), secure the die and continue sizing but with a feeler gage between the deck of the shell holder and bottom of the case, this sizes the case for short chambers, I short chambers first, then road test, if after road testing I like the results, I finish the chamber.
In the perfect world the belted case can not be shimmed up more than .004 to .005 thousands, that is the reason I cut the belt off when checking for short chamber.
F. Guffey