Yes, the "entrance" radius on my barrel is quite generous. But that turned out to be a good thing as it allowed the case to blow through the extractor cut-out and vent the pressure. Otherwise, the bolt would have failed. Keep in mind that the pressure was WAY over the design limit as indicated by the massive flow of brass.
I have added one picture to show how the barrel geometry will allow the bulged case head to fit between the barrel and a closed bolt.
Around Christmas, I will post more photos with actual case dimensions compared to a unfired and a "normally" fired case from the same gun.
Thanks to all for the input and suggestions.