I would take the brake off, have a good look at the crown for damage, and any marks on the inside of the brake. Then try shooting it without the brake on. If you see anything not right on the crown, or any marks inside your brake, sent it back for repair. On my neighbor's rifle, when the local gunsmith, threaded the barrel for the brake, he damaged the crown, and end of barrel abit. They ended up cutting off the damaged part of the barrel, but a 21 inch barrelled 300 Win isn't much better than a hot loaded 30-06.
Rob