The tumbling process is also what creates the slight dish in the factory bolt faces, and the elimination of the dish is the ONLY advantage an off the shelf PT&G bolt head would have over a factory one.
This is my understanding as well. I cut the shank off of an old bolt face, I assure you it is not powdered metal, MIM, ect. It's very tuff stuff! Articles such as this one, is the partial root of the misinformation:http://bulletin.accurateshooter.com/...-savage-bolts/