The actions on these rifles often don't lock up tightly, allowing a little case stretch. If you don't full-length resize, the reloads may be oversized enough not to chamber properly. The same can happen with some bolt actions, though. I had a little Remington in .308 (I forget the model number; 600, maybe?) which didn't have the locking lugs at the front of the bolt. The lugs were at the rear by the bolt handle, and it allowed enough case stretch that on the 3rd reload, neck sizing the case, the bolt wouldn't close. On the other hand, my Win. 88 which has the rotating lugs at the front of the bolt has no problems with neck sized brass. I would suggest that you try neck sizing, but before priming the cases run them through your action to see if they will chamber properly. If not you will need to go to the full length sizing die.
-Kees-