To add to Miller's position that a rough chamber surface didn't cause this failure, I don't believe any degree of roughness would hurt significantly. Barrel steels are mallable and therefore notch tolerant. Think about the engraving and roll marking that makers and customizers put on the o.d. of the chamber. The o.d. is the most stressed surface when compared to the i.d.. Pits in the chamber or cutter marks wouldn't make much difference.
I'm of the belief that this was a cartridge pressure issue. Since they wwere shooting Rem compression formed hulls, I don't buy into the notion that a basewad lodged in the bore.
