At the range today sighting in a friends 300-378 Weatherby Mag. It's a stock Mark 5 action and stock, no custom work. Using Weatherby Factory ammo 180 grn Nosler AB. First shot bolt is stiff, like pry on it stiff. Second shot bolt stuck, I open up with mallet and primer is blown, both show major extractor marks. Rifle is in great shape barrel is clean, no obstructions etc. . . Needless to say I am done shooting it. Ammo is about 4 years old I am told, temp was hot 105 but ammo not left in sun, came out of truck. What are he possible issues, yes I will have it looked at of course.