I don't see it that way. If the chamber is "long to the shoulder" than the brass will stretch and thin ahead of the belt.
But he said his cases looked normal with no signs of pressure. If they were stretching to the point of failure him and his experts, whoever they are would have noticed.
Hence my earlier comment about my not arguing pro-OP.
I'm merely addressing a particular point about belted cases and official vs. actual headspace.
