Well - You stated that you were able to lift the bolt handle while seized. That eliminates lug setback. This is indicative of the round sticking in the chamber. Have you tried?
1) With the handle lifted, grab the rifle firmly and give a good thump to the butt pad against the floor.
2) Go buy a length of steel rod from Can Tire, slightly undersize to the bore, and insert from muzzle end. Again, with handle lifted, tap the rod with a hammer.