I had this happen with one particular batch of ammo. In searching for a solution it appears at least a handful of others have had this issue--I have heard tikka holds headspace to pretty close tolerances, but my guess is that they hold it to the small-end of the allowable tolerance? So any ammo that is at the large-end of aceptable length or slightly over would cause this. In my case, I sent the ammo back to the manufacturer who said they would replace it no questions asked...aside from waiting forever for replacement, that's great. But sounds like you have it with a bunch of ammo, so perhaps its even smaller? Anyway, if you tried multiple brands of ammo and they are all hard close/open and your other bolt also is hard open/close, it sure sounds like a headspace problem caused by the barrel or the action. What caliber is it? Maybe someone has headspace gauges you could borrow to at least get a definitive sense of the problem that you could use to work with beretta? (i.e. send them a video of it not closing on the go gauge with both bolts or something like that and they are more likely to go right to the proper fix?). Did you buy the gun through a retailer that could help you or help get you in touch with someone at beretta that could offer some guidance?
Edit: I see you said it was also a 270. Know anyone local with a 30-06/270 go gauge?