First of all, the cases are not being sized enough if they won't fit into the chamber. Your friend needs to get a full length resizing die. He should also try the resized case in the chamber of the rifle he is using before going any further.
Otherwise, if it's not the case resizing, I would suspect either he has the bullet seated so far out that the bullet is contacting the lands, preventing the round from fulling seating. I doubt this though. Or that he is not trimming his cases to the required specs.
Could be that the die is out of spec. It is hard to tell what's wrong by the info you gave. Have your friend tell you step by step how he processes the cases and report back. Also, info on the rifle would help. Could be that the headspace is too short. We just need more info.