What is happening to you also happened to my brother. we tried different dies and the same thing happened. we sent the rifle back and when we got it same thing. we talked to our gunsmith and he said that is a problem that a lot of gunmakers have with trying to chamber the short mags. Because they take the same short actions that they use with a .308 case and modified it to fit a short mag. The only company that I know of that chambers the short mag to exact diminsions is Kimber. If the dies do not work I would send the rifle in and try to get a new one. If they send you a new one you will most likely not have the same problem.
