To check the locking bolts, clean off the top surface and color it with a marker. When you close the action and then open it again you'll be able to see how much engagement there is. Based on your description, I'd guess not enough. Can either carefully stone down the top surface so it locks up better or replace them and see if that works.
With new barrels I always pull out the bolts and extractor to clean all that stuff up regardless.
